Graphs and Charts Describing Different Types of Motion4(A): Generate and interpret graphs and charts describing different types of motion,

including the use of real-time technology such as motion detectors or photogates.

Vocabulary

displacement: The difference between the final position and initial position of an object.

average velocity: The displacement of an object divided by the time interval over which the displacement

occurred.

acceleration: the change in velocity over time

simple harmonic motion: movement that repeats over and over again

Key Concepts

A moving object travels from one position to another. The length of a straight line between the initial position

and the final position is called the displacement.

The average velocity of an object is its displacement, or change in position, divided by the time interval over

which the displacement occurs. Velocity is associated with direction, while speed is the same measurement

without direction. An example of velocity is 4 m/s due east, while an example of speed is 4 m/s.

A position-time graph plots position over time. A velocity-time graph plots velocity over time. The shape of either

graph provides information about the motion of an object. For example, the slope of a position-time graph

represents average velocity.

An object can travel at a constant velocity or it can accelerate, meaning that its velocity changes. An accelerating

object can be speeding up, slowing down, or changing direction.

An object traveling in a circle, even if its speed does not change, is accelerating because its direction is changing.

The average velocity of an object can be calculated by measuring the distance it travels and the time during

which it travels that distance. Such measurements can sometimes be difficult to obtain by hand, and tools such as

motion detectors and photogates can be used to obtain more accurate data.

Simple harmonic motion describes the movement of an object whose action is repeated over and over again. If

you have ever ridden on a Ferris wheel, then you have experienced simple harmonic motion. Likewise, a bob

bouncing up and down on the end of a hanging spring is an example of simple harmonic motion.

Motion in One Dimension

4(B): Describe and analyze motion in one dimension using equations with the concepts of

distance, displacement, speed, average velocity, instantaneous velocity, and acceleration.

Vocabulary

displacement: the difference between the final position and initial position of an object

instantaneous velocity: the velocity at any given instant while an object is in motion

average velocity: the displacement of an object divided by the time interval over which the displacement

occurred

acceleration: the change in velocity divided by the time interval during which the change occurred

Key Concepts

A moving object travels from one position to another. The length of a straight line drawn from the initial position

to the final position is called the displacement. Displacement can be determined from the following equation:

The average velocity of an object is its displacement, or change in position, divided by the time interval over

which the change occurred. Velocity is associated with direction, while speed is the same measurement without

direction. An example of velocity is 4 m/s due east, while an example of speed is 4 m/s. Average velocity can be

determined from the following equation:

The rate at which velocity changes is known as acceleration. An object's acceleration can be calculated by dividing

the change in velocity by the time during which that change occurred. Acceleration can be determined from the

following equation:

Accelerated Motion in Two Dimensions4(C): Analyze and describe accelerated motion in two dimensions using equations,

including projectile and circular examples.

Vocabulary

projectile motion: free fall with an initial horizontal velocity

trajectory: the path of a moving body, such as a projectile, through space

uniform circular motion: motion of an object in a circle at constant speed

centripetal force: inward force exerted on an object moving in a circle

Key Concepts

The motion of a car traveling along a road or a squirrel climbing a tree is motion in one dimension. Many

examples of motion, however, are in two dimensions. For example, a baseball thrown by a pitcher moves

horizontally toward the batter. The ball also moves vertically as it falls toward the ground.·

The motion of the baseball is an example of projectile motion. An object with projectile motion falls downward

because of gravity, but it also has horizontal velocity. The path, or trajectory, of a projectile is a curve called a

parabola.

An object moving in a circle, even at constant speed, is accelerating because its direction is constantly changing.

The force that causes the object to accelerate in this way, called centripetal force, is directed toward the center of

the circle.

Calculate the Effect of Forces on Objects

4(D): Calculate the effect of forces on objects, including the law of inertia, the relationship

between force and acceleration, and the nature of force pairs between objects.

Vocabulary

law of inertia: the law that states that an object at rest remains at rest and an object in motion stays in motion at

constant speed unless an unbalanced force acts upon it; also known as Newton’s first law of motion

Newton’s second law of motion: the law that states that the acceleration of an object is directly proportional to

the magnitude of the net force acting on it and inversely proportional to the mass of the object

Newton’s third law of motion: the law that states that for every pair of objects that interact, equal but opposite

forces act on the objects

weight: the force that results from the gravitational pull on an object; W = mg

normal: the force that an object in contact with another object exerts on that object, perpendicular to the plane

of contact, so that the second object does not pass through the first

friction: the force that arises between two surfaces in contact with each other and opposes motion along the

surfaces

Key Concepts

An unbalanced force is required to change the motion of an object. Without an unbalanced force, an object at

rest remains at rest and an object in motion remains in motion at constant velocity. This is known as the law of

inertia.

An unbalanced force causes an object to accelerate by speeding up, slowing down, or changing direction. The

magnitude of the acceleration is directly proportional to the force and inversely related to the mass according to

the equation a = F/m , where F is the unbalanced force, m is the mass of the object, and a is the acceleration. This

is explained as Newton’s third law of motion

For every action, there is an equal and opposite reaction. Therefore, if you push against a wall with a force of 8

newtons (N), the wall pushes back on you with a force of 8 N. This is explained as Newton’s third law of motion.

Free Body Diagrams4(E): Develop and interpret free-body force diagrams.

Vocabulary

force: a push or a pull

magnitude: the strength of a force

vector: any quantity that has magnitude and direction

free body diagram: a diagram that shows all the external forces acting on an object

Key Concepts

A force is a push or a pull. The magnitude of a force is its strength. A force is a vector quantity, meaning it is

described by both a magnitude and a direction. Velocity, acceleration, and displacement are also vector

quantities. Vectors are drawn as arrows. The length of the arrow denotes magnitude, and the arrow's angle in

relation to the horizontal or vertical axis denotes direction.

A free body diagram is a diagram of external force vectors acting on an object. The object is usually depicted as a

rectangle, circle, or dot with force vectors pointing at various angles toward or away from it. The diagram often

includes an x-y coordinate grid, with the center of the object placed at the origin. The vectors should be either

drawn to scale or have lengths drawn relative to one another.

In the example shown below, the vectors show three forces acting on an object. Two forces each have a

magnitude of 5 N. The third force has a magnitude of 6 N. The direction of each vector arrow shows the

directions of the force.

A force that points upward or to the right can be described as a positive force. Similarly, a force that points

downward or to the left can be described as a negative force. In the diagram below, positive and negative

magnitudes have been assigned to each force. The net force acting on the object is zero.

Free body force diagrams are useful tools for resolving force vectors in their x and y components and to find the

net force acting on an object. If the net force is greater than zero, there is acceleration in its direction. This

acceleration vector can be drawn as well. In the example shown below, the net force that acts on the object is a

force to the right of 3 N. Notice that the upward and downward forces are equal and opposite, so their effects

cancel each other out.

Frames of Reference4(F): Identify and describe motion relative to different frames of reference.

Vocabulary

frame of reference: a set of axes used to measure the position or motion of an object

inertial frame of reference: a frame of reference in which the observer is either traveling at a constant velocity or

is stationary

noninertial frame of reference: a frame of reference in which the observer is accelerating

special theory of relativity: a description of time, matter, and energy as the speed of particles approach the

speed of light

time dilation: the slowing of time from the frame of reference of an object traveling at nearly the speed of light

length contraction: the contraction of length from the frame of reference of an object traveling at nearly the

speed of light

Key Concepts

You may feel that you are not moving when you are seated in a chair and reading a book, a page, or a computer

screen, such as this one. However, the calculation of movement and position depends on a frame of reference.

You may be at rest with respect to the frame of reference of the school or your house. You are moving, however,

with respect to the solar system. Remember that Earth—and everything upon it—rotates like a top and revolves

around the Sun.

An inertial frame of reference is a system that is stationary or that moves at a constant velocity. An example is a

car, train, or airplane that is traveling at a constant velocity along the ground or in the air. Remember that

velocity is both speed and direction. If you are in a car traveling 60 kilometers per hour on a straight highway, and

if the ride is smooth, then you would feel as motionless as if you were sitting in a chair at school.

If a car suddenly veers to the left or right, if it slows down or speeds up, or if a bump in the road alters the car’s

motion, then the car becomes a noninertial frame of reference. Even if you are strapped in tightly to the seat

behind you, you would feel a force from the car’s acceleration. Remember that acceleration is a change in

velocity and may involve a change in speed, a change in direction, or a change in both speed and direction.

Physicist Albert Einstein (1879–1955) applied ideas about frames of reference to develop the special theory of

relativity, which involves objects in motion that approach the speed of light. The theory depends on two

postulates, or statements that are believed to be true:

1. The speed of light is the same for all observers, regardless of their frame of reference.

2. The laws of physics are the same in every inertial frame of reference.

As a consequence of these postulates, Einstein redefined time, length, mass, and energy as they applied to

particles

moving nearly as fast as the speed of light.

Time dilation involves a difference in time between two frames of reference. For time dilation to be significant,

the frames of reference must differ by nearly the speed of light. For example, if an astronaut travels in a

spaceship that approaches the speed of light, time would pass very slowly on the ship from Earth’s frame of

reference. While the astronaut experiences a one-month journey aboard the ship, half a year or longer might

pass on Earth.

Length contraction involves a difference in observed length between two frames of reference. Aboard the

spaceship, the astronaut would observe distances on Earth or other places to be much shorter than their actual

distances at rest.

As an object’s speed approaches the speed of light, its mass also increases from the frame of reference of a

stationary observer. Kinetic energy depends on mass, so the kinetic energy also increases. At the speed of light,

an object would have infinite mass and infinite kinetic energy, which is why accelerating an object to the speed of

light is not possible.

Historical Development of the Concepts of Different Forces5(A): Research and describe the historical development of the concepts of gravitational,

electromagnetic, weak nuclear, and strong nuclear forces.

Vocabulary

gravitational force: a force of attraction between any two masses in the universe

electromagnetic force: an attractive or repulsive force that acts between charged particles

weak nuclear force: a force that is exerted over the short distances within atoms and is responsible for certain

forms of radioactivity

strong nuclear force: a force that holds the nucleus of an atom together against the repulsion of the protons

Key Concepts

Of all the interactions that occur in the universe, scientists have identified four basic, or fundamental, forces that

can be used to explain physical events.

The first fundamental interaction to be identified and described mathematically was gravitation. Galileo Galilei

first asserted that objects fall at the same rate regardless of their mass. Isaac Newton published his universal law

of gravitation in 1687, which gave a basic understanding of how gravity works. Albert Einstein took Newton’s

ideas a step further in 1916 with his general theory of relativity, which described space and time as curved by the

effects of gravity.

Of the four fundamental forces, the gravitational force has the weakest magnitude, but it can act over long

ranges. It is always an attractive force, and it acts between any two masses in the universe.

People have known about magnets and electrical phenomena, such as lightning, for millennia. The study that led

to the modern understanding of these forces began with William Gilbert around the turn of the seventeenth

century. Later, many scientists, including Charles Augustin de Coulomb, Simeon-Denis Poisson, Carl Friedrich

Gauss, and Michael Faraday, further investigated these forces and identified laws governing electrical or

magnetic force. In 1864, James Clerk Maxwell developed what came to be called Maxwell’s equations, which

mathematically described electromagnetism as a single interaction.

Electromagnetic force acts between particles of matter that carry an electric charge. It can involve attraction or

repulsion, and it can act at a distance. This force can hold atoms together, and it is also the force that can push

two magnets apart.

All matter is made up of atoms. The nucleus of an atom is made up of protons, which have a positive electric

charge, and neutrons, which are electrically neutral. Because particles with the same electric charge repel one

another, a force must exist to hold the nucleus together. Scientists have identified this force as the strong nuclear

force.

The existence of the strong nuclear force was theorized before it was observed. As early as 1934, Hideki Yukawa

theorized the existence of mesons, the particles responsible for the strong nuclear force that holds a nucleus

together. The first actual meson was not detected until 1947. A team at the University of Bristol led by Cecil

Powell found the pi-meson, or pion, in cosmic rays. Since that time, technological advances have given scientists

the ability to produce and detect more mesons. Particle accelerators can propel tiny bits of matter to huge

speeds and smash them apart. Bubble chambers can give pictures of the paths of charged mesons.

Mesons bind together quarks, the particles that make up protons and neutrons. Quarks in neighboring protons

and neutrons can sometimes exchange mesons. This binds protons together inside the nucleus.

The strong nuclear force acts over a very short range. Neutrons increase the amount of strong nuclear force

within the nucleus and thus act to balance the proton-proton electric repulsive forces.

The weak nuclear force is observed when unstable atoms give off certain particles and energy, a process known

as radioactive decay. The weak nuclear force acts across even smaller distances than the strong nuclear force.

Enrico Fermi first postulated the existence of the weak nuclear force in 1933 in order to explain beta decay.

Richard Feynman and Murray Gell-Mann gave a more complete definition of the weak interaction about 25 years

later. Their theory helped scientists predict how the weak nuclear force would affect reactions and particles in

various situations.

Magnitude of the Gravitational Force5(B): Describe and calculate how the magnitude of the gravitational force between two

objects depends on their masses and the distance between their centers.

Vocabulary

Law of Universal Gravitation: a law that states that a force of attraction exists between any two masses in the

universe and that the magnitude of the force is directly proportional to the product of the masses and inversely

proportional to the square of the distance between them

directly proportional relationship: a relationship between two quantities in which one quantity changes in the

same way as the other, either increasing or decreasing as the other quantity does the same

inversely proportional relationship: a relationship between two quantities in which one quantity decreases as

the other quantity increases

gravitational constant: a proportionality constant that is a positive number and has a value of 6.67x10-11

Nm2/kg

2

Key Concepts

In 1687, Isaac Newton proposed the Law of Universal Gravitation, which is based on observations of falling

bodies. According to the law, the gravitational force between two objects is directly proportional to the product

of their masses and inversely proportional to the square of the distance between the centers of their masses:

The Law of Universal Gravitation explains why objects fall toward Earth s surface and why objects such as the

moon and planets can orbit other objects. No one before Newton had described Earth-bound and planetary

motion with the same theory.

As explained by the Law of Universal Gravitation, the gravitational force between two objects increases as the

mass of one object or both objects increases, and it decreases as the distance between the objects increases.

Magnitude of the Electrical Force5(C): Describe and calculate how the magnitude of the electrical force between two objects

depends on their charges and the distance between them.

Vocabulary

electrostatic force: the attractive or repulsive force between two charged objects

electrostatic constant: the constant k used to calculate the magnitude of the electrostatic force:

Coulomb’s law: the electrostatic force between two objects is proportional to the strength of their charges and

the inverse square of the distance between them

conductor: a material through which electrons flow easily

insulator: a material resistant to electron flow

Key Concepts

Opposite charges attract each other, and like charges repel each other.

Coulumb’s law states that the electrostatic force F between two point charges Q1 and Q2 is given by the

equation:

F = ,

in which k is the electrostatic constant, and r is the distance between the two charges.

The electrostatic force is a central force that is directed along an imaginary line joining the two charges.

The force on one charge is equal in magnitude and opposite in direction to the force on the other charge.

Examples of Electric and Magnetic Forces5(D): Identify examples of electric and magnetic forces in everyday life.

Vocabulary

electric field: a region of space in which an electric force has an effect

magnetic field: a region of space in which a magnetic force has an effect

electromagnetic force: the fundamental force of attraction or repulsion due to electric charge

electromagnetic wave (also called electromagnetic radiation): a wave that travels through space as alternating

magnetic and electric fields

static electricity: a charge separation between stationary objects

electrostatic discharge: a brief exchange of electric charge between two objects of different electric potentials

electric current: a flow of electric charge

electromagnet: an item made to temporarily act as a magnet by exposure to an electric current

magnetic domain: a region in a magnetic material with a given magnetization

degauss: to remove a magnetic field from an object by exposure to a higher field

electromagnetic induction: the production of electric potential difference in a conductor as it moves through a

magnetic field

Key Concepts

Electric forces are a result of small charged particles, such as protons and electrons. Protons have a positive

charge, and electrons have a negative charge. Like charges repel one another, while unlike charges attract each

other. An electric field is the region around electric charges that the charges affect.

Magnetic forces result from the motion of charged particles. The forces involve two poles, designated north and

south, that repel and attract one another similarly to opposite electric charges. In a permanent magnet, the

motion of certain electrons aligns in such a way as to create a magnetic field, a region around the magnet that

the magnetic force affects.

The Earth itself acts as a magnet, and compass needles align with the Earth's magnetic field.

Together, electricity and magnetism form the electromagnetic force, one of the four fundamental forces in

nature.

An electromagnetic wave, which is also called electromagnetic radiation, travels as oscillating magnetic and

electric fields. The changing magnetic field induces an electric field, and the changing electric field induces a

magnetic field.

Electrons may accumulate through contact between items, producing static electricity effects, including

electrostatic discharge. Lightning is an example of a very large electrostatic discharge.

An electric current produces a magnetic field. In manmade electromagnets, magnetic domains of iron cores are

aligned with and boost the magnetic field produced by the electric current. Electromagnets are used in many

applications in everyday life, such as spark plugs in a car, transformers, motors, and loudspeakers.

Electromagnets are used to degauss antitheft tags in books in a bookstore after purchase.

An electric current can also be induced in a conductor as it moves through a magnetic field. This is called

electromagnetic induction. By rotating a coil of wire through a magnetic field, electricity can be generated in

power plants and generators.

Characterize Materials as Conductors or Insulators5(E): Characterize materials as conductors or insulators based on their electrical

properties.

Vocabulary

conductor: a material through which electrons flow easily

insulator: a material resistant to electron flow

Key Concepts

Conductors allow an easy flow of electrons between atoms, while insulators resist electron flow.

Whether a material is a conductor or an insulator is intrinsic to its atomic structure.

If the electrons are tightly bound to the atoms of a material, it is likely to be an insulator, whereas materials with

loosely bound atoms are conductors.

Metals are generally good conductors.

ectric Current, Potential, Resistance, and Power5(F): Design, construct, and calculate in terms of current through, potential difference

across, resistance of, and power used by electric circuit elements connected in both series

and parallel combinations.

Vocabulary

current: the rate at which electric charge flows past a given point in an electric circuit, measured in amperes (A),

or amps for short

electric potential: the amount of potential energy per unit charge, measured in volts (V)

resistance: the opposition to the flow of electric charge, measured in ohms (Ω)

electric circuit: a complete loop of conductors through which electric current can flow

series circuit: an electric circuit in which current can flow through a single path

parallel circuit: an electric circuit in which current can flow through two or more distinct paths

power: the rate at which energy is transformed, measured in watts (W)

Key Concepts

Electric current requires a closed conducting path that connects the two terminals of a voltage source. This closed

path is called an electric circuit.

An electric circuit consists of a voltage source (such as a battery), conducting wires, and resistors. The resistors

may be light bulbs, bells, or other devices that oppose the flow of current. In circuit diagrams, a resistor is

indicated by a zigzag line and the letter ‘R.’

Electric circuits can be wired in different ways. In a series circuit, the resistors are arranged in a single path. In a

parallel circuit, the resistors are arranged in separate paths, or branches.

If one resistor in a series circuit is removed from the circuit, such as by unscrewing a bulb, the circuit is broken

and current ceases to flow. As more resistance is added to a series circuit, the overall current through the circuit

decreases.

If one resistor in a parallel circuit is removed from the circuit, current continues to flow through the other paths.

As more resistance is added in one path of a parallel circuit, the overall current through the circuit increases.

Current (I ), voltage (V ), and resistance (R ) are related according to the equation V = IR . This equation holds true

across any two points of a circuit.

Power (P ) is measured in units of watts (W ). One watt is equal to 1 joule per second. In any device connected in

an electric circuit, the power (P ) transformed is equal to the product of the current (I ) and potential difference

across the device (V ). In equation form: P = IV .

For a series circuit, the total resistance of the circuit is the sum of the individual resistors: R T = R 1 + R 2 + R 3

For a parallel circuit, the total resistance of the circuit is given by this formula:

The Relationship between Electric and Magnetic Fields5(G): Investigate and describe the relationship between electric and magnetic fields in

applications such as generators, motors, and transformers.

Vocabulary

electric motor: a device that converts electrical energy into mechanical energy; can be used to do work

electromagnetic induction: the production of voltage in a wire when it moves within a magnetic field

electric generator: a device that converts mechanical energy into electrical energy, such as at an electric power

plant

transformer: a device that uses electromagnetic induction to convert one voltage to another

Key Concepts

In an electric motor, a coil of insulated wire is wrapped around an iron core. The coil is able to rotate freely

between the poles of a permanent magnet. The coil of wire and the iron core form an electromagnet, which

produces a magnetic field that interacts with the magnetic field of the permanent magnet. By attaching the

spinning coil to a shaft, the motor can turn wheels, propellers, or other objects.

In 1831, Michael Faraday discovered that moving a magnet in and out of a coil of wire produces an electric

current in the wire. Moving a coil of wire through a magnetic field also produces an electric current. The process

is known as electromagnetic induction. The current produced is called an induced current.

An electric generator includes a rotating coil of wire through a magnetic field. This induces a current in the wire.

Electric power lines carry electric current across long distances. They do so at high voltage and low current,

conditions that minimize the loss of energy to heat. Near a house or building, the electricity is transformed to low

voltage and high current.

Transformers are devices that apply the principle of magnetic induction to increase or decrease voltage. Step-up

transformers increase voltage; step-down transformers decrease voltage.

Strong and Weak Nuclear Forces in Nature5(H): Describe evidence for and effects of the strong and weak nuclear forces in nature.

Vocabulary

nucleon: a particle in an atomic nucleus; proton or neutron

isotope: a form of an element in which the atoms have the element's characteristic number of protons but a

unique number of neutrons

nuclide: the nucleus of an isotope of an element

mass number: the total number of protons and neutrons in the atomic nucleus

radioactive decay: the process through which an unstable nucleus emits particles and energy in order to become

stable

radioactive half-life: the time it takes for half of a sample to decay

strong nuclear force: the force of attraction that holds nucleons together despite the repulsive electric force

between protons

weak nuclear force: the force responsible for beta decay and certain other changes to atomic nuclei

Key Concepts

A stable nucleus does not change. An unstable nucleus emits radiation in the form of particles or energy.

Examples of radiation include alpha decay (the release of a helium nucleus) and beta decay (the release of

electrons). An unstable nucleus continues emitting radiation until it becomes stable.

When scientists discovered that a nucleus consists of positively charged protons and neutral neutrons, they

recognized that a force must hold the nucleons (protons and neutrons) together. The force is called the strong

nuclear force. It is an attractive force that exists between two nucleons.

The strong nuclear force is effective at extremely small distances, but decreases very quickly with distance. For

this reason, this force is significant only between neighboring nucleons.

The weak nuclear force, though still strong in magnitude, was named because it is weaker than the strong nuclear

force. Like the strong nuclear force, it is effective only over very short distances within atomic nuclei. It is used to

explain beta decay and other types of changes in the nucleus.

Investigate and Calculate Quantities6(A): Investigate and calculate quantities using the work-energy theorem in various

situations.

Vocabulary

work (W ): the product of the net force exerted on an object (F ) and the distance (d ) through which that force

causes the object to move;

W = Fd

kinetic energy (KE ): the energy associated with the motion of an object; depends on mass (m ) and speed (v )

according to the expression

work-energy theorem: the net work done on an object by a force is equal to the change in the kinetic energy of

the object; W = ΔKE

Key Concepts

Work is done when a net force exerted on an object causes the object to move some distance in the direction of

the force. Gravity, for example, does work on falling objects. You do work against gravity when you lift an object

over your head.

According to the work-energy theorem, the change in the kinetic energy of an object is equal to the work done on

the object. The work-energy theorem is based on the fact that the total energy of a system is conserved.

Analyzing motion according to the work-energy theorem is often easier than using other equations. When used

correctly, however, both approaches will yield the same results.

Kinetic and Potential Energy and Their Transformations6(B): Investigate examples of kinetic and potential energy and their transformations.

Vocabulary

energy: a quantity that changes or has the ability to change an object by modifying its state, temperature,

position, speed, pressure, or any other physical characteristic, measured in joules

potential energy: energy due to an object’s position, measured in joules

kinetic energy: energy due to an object’s speed, measured in joules

mechanical energy: the potential or kinetic energy an object possesses

work: the product of force multiplied by distance, measured in joules

law of conservation of energy: law stating that energy cannot be created or destroyed

work-energy theorem: theorem stating that when work is done on an object, its total energy changes

Key Concepts

Energy is a quantity that creates or can create change with respect to an object’s position, speed, temperature,

pressure, or any other physical characteristic. Energy can be divided into different types; thermal energy,

electromagnetic energy, chemical energy, and mechanical energy. Mechanical energy is further divided into two

types: potential energy, or the energy of position, and kinetic energy, or the energy of motion.

When you do work on an object—that is, apply a force through a distance—you are changing the energy of the

object. This principle is called the work-energy theorem. For instance, when you lift a 10-kg box to place it on a

shelf 2 m high, the work you do on the box is stored as potential energy. You can calculate the energy by

multiplying the mass, 10 kg, by the acceleration due to gravity, 9.8 m/s2, and the height, 2 m, as represented in

the equation E potential = mgh . This is the same calculation as W = Fd , where W is work, F is force (equal to the

weight, 98 N), and d is the height through which the force acts, in this case, 2 m.

Were you to push the box off the shelf, potential energy would transform into kinetic energy. When the box is at

half the shelf’s height, the total energy would be divided evenly into half potential and half kinetic. For instance,

if 196 J of work is done to the box to put it on the shelf, it is stored as 196 J of potential energy as long as the box

rests on the shelf. At this point, the kinetic energy is zero. Push the box off of the shelf, and halfway down, the

box will have 88 J of potential energy and 88 J of kinetic energy. Just before it hits the ground, it has no potential

energy and 196 J of kinetic energy.

The transformation of energy from one form to another always abides by the law of conservation of energy,

which states that energy is neither created nor destroyed. If the box were dropped in a vacuum, all of the

potential energy would convert to kinetic energy. When the box falls through the air, however, some of the

energy is changed into thermal energy by way of air friction.

Mechanical Energy, Power, Impulse and Momentum in Physical

Systems6(C): Calculate the mechanical energy of, power generated within, impulse applied to, and

momentum of a physical system.

Vocabulary

mechanical energy: the energy associated with the position and movement of an object, equals the sum of the

kinetic energy and potential energy

potential energy (PE): the energy associated with the position of an object; for gravitational potential energy,

equals the product of the mass (m ) and height (h ) of the object, and the constant of acceleration due to gravity

(g )

kinetic energy (KE): the energy associated with the motion of an object; depends on mass (m ) and speed (v )

according to the expression

mv2

law of conservation of energy: the well-verified principle that total energy is conserved in any physical or

chemical change to matter

momentum (p ): the product of the mass (m ) and velocity (v) of an object

law of conservation of momentum: the well-verified principle that the total momentum of a system of moving

objects is conserved

power: work per unit of time, measured in watts (W)

impulse: the change in momentum over time; equals the product of the net force on an object and the time

during which the force acts

Key Concepts

When moving objects collide with one another, they may bounce off, stick together, or break apart. Objects may

also change their speed, direction, or both speed and direction. In all cases, however, both the total energy and

total momentum of the objects is conserved.

Mechanical energy is the sum of potential energy (such as the energy due to an object’s height or the

compression of a spring) and kinetic energy, which is the energy due to motion. The degree to which mechanical

energy is conserved depends on the loss of energy to heat, an event that occurs in nearly all physical systems.

This is why a rolling marble or a sliding hockey puck eventually slows to a stop.

When two objects collide, each experiences an impulse from the other. An impulse is a change in momentum,

such as happens during a collision. For example, if a moving billiard ball has momentum of 0.70 N • s before a

collision with a wall, then a momentum of −0.70 N • s after the collision (meaning it bounced backward), then it

experienced an impulse of −1.4 N • s from the wall. The negative sign indicates the direction of the force.

The Laws of Conservation of Energy and Conservation of

Momentum6(D): Demonstrate and apply the laws of conservation of energy and conservation of

momentum in one dimension.

Vocabulary

potential energy (PE ): the energy associated with the position of an object; for gravitational potential energy,

equals the product of the mass (m ) and height (h ) of the object, and the constant of acceleration due to gravity

(g )

kinetic energy (KE ): the energy associated with the motion of an object; depends on mass (m ) and speed (v )

according to the expression

mv2

law of conservation of energy: the well-verified principle that total energy is conserved in any physical or

chemical change to matter

momentum (p ): the product of the mass (m ) and velocity (v ) of an object

law of conservation of momentum: the well-verified principle that the total momentum of a system of moving

objects is conserved

elastic collision: a collision in which the total kinetic energy of the system is conserved, such as when two moving

marbles bounce off each other

inelastic collision: a collision in which kinetic energy is lost, typically to heat

Key Concepts

The momentum of a moving object is equal to the product of its mass and velocity (mv ). Be sure to recognize,

however, that velocity is a vector quantity, meaning it includes a magnitude and direction. This means that

momentum is also a vector quantity.

In any system of moving objects, the total momentum of the objects is conserved. If a system of two billiard balls

has a forward momentum of 0.50 kg m/s before a collision, the system will have the same quantity and direction

of momentum after the collision.

Energy can be neither created nor destroyed, but it can change form. In an elastic collision, the total kinetic

energy of the colliding objects remains the same. In an inelastic collision, a significant amount of kinetic energy is

changed into heat or other forms of energy.

Two marbles bouncing off each other are an example of an almost completely elastic collision. A car crash,

especially a head-on crash, is an example of an inelastic collision.

Macroscopic Properties of a Thermodynamic System6(E): Describe how the macroscopic properties of a thermodynamic system such as

temperature, specific heat, and pressure are related to the molecular level of matter,

including kinetic or potential energy of atoms.

Vocabulary:

macroscopic properties: properties of matter that can be readily observed or measured without intense

magnification; opposite of microscopic properties

heat: a form of energy that flows from an object of higher temperature to one of lower temperature

temperature: a measure of the average kinetic energy of particles in matter

law of conversation of energy: law stating that energy is neither created nor destroyed in any process that

involves physical or chemical changes to matter

heat capacity: the amount of heat required to increase the temperature of an object by 1°C

specific heat: the amount of heat required to raise the temperature of 1 g of a substance by 1°C

Key Concepts

According to the particle model of matter, all matter is made of tiny particles (such as atoms, ions, or molecules)

that are in constant motion. This model explains many of the macroscopic properties of matter, including the

behavior of solids, liquids, and gases.

In a solid, particles are in fixed positions but have vibrational energy, meaning they move back and forth rapidly.

Vibrational energy involves a continuous interconversion of kinetic and potential energy.

Kinetic theory is used to explain the specific behaviors of gas particles. One postulate of kinetic theory is that gas

particles are in constant random motion. Another postulate is that the volume of a gas is due to the motion of the

particles, not to the relatively small and insignificant volume of the particles themselves.

The temperature of a sample of matter is a measure of the average kinetic energy of the particles. Temperature

can be measured on different scales, including degrees Celsius and degrees Fahrenheit.

As heat is added to a substance, the energy of the particles increases. This increases their motion. Particles can

gain kinetic energy, moving about more rapidly. They can also gain potential energy, stored as vibrations of

particles, including different atoms within a molecule.

The Kelvin scale (K) measures absolute temperature, which is directly proportional to the average kinetic energy

of particles.

Pressure is defined as force per unit area. As explained by kinetic theory, a gas exerts pressure on its container

because its particles collide with the container wall. Increasing the temperature increases the average speed of

the particles and thus increases the pressure they exert.

The heat capacity of a substance is a measure of the amount of heat required to raise the temperature by 1°C.

Specific heat is the heat capacity of 1 g of a substance.

A substance that can store potential energy as the vibration of its molecules can absorb a large amount of heat

and thus has a high heat capacity.

Processes of Thermal Energy Transfer6(F): Contrast and give examples of different processes of thermal energy transfer,

including conduction, convection, and radiation.

Vocabulary

thermal energy: energy due to the kinetic energy or motion of the particles in a substance

heat: the flow of thermal energy. Heat flows due to a difference in temperature, from hot to cold. Heat is

measured in Joules.

heat conduction: heat transfer by particles in direct contact with one another

thermal equilibrium: absence of heat flow between two objects because their temperatures are equal

thermal conductor: a substance that conducts heat easily

thermal insulator: a substance that conducts heat poorly

convection: heat transfer by currents in liquids or gases

thermal radiation: a type of heat transfer created by electromagnetic waves

Key Concepts

Thermal energy is the total kinetic energy of the particles (atoms and molecules) of a substance. Because all

particles have motion, everything has thermal energy. Thermal energy is related to temperature and mass,

where temperature is defined as the average kinetic energy of the particles. For instance, a burning match is hot

and therefore has a high temperature; its molecules are moving fast. An ice sculpture is cold and has a low

temperature because its molecules are moving slowly. The thermal energy of an ice sculpture would be greater,

however, because it has many more particles than the match, even though the ice sculpture’s particles are

moving at slow speeds.

Heat is the flow of thermal energy anytime there is a difference in temperature. For instance, when you touch a

cup of hot chocolate, it feels warm. The heat from the cup is traveling into your hand, which is colder.

Heat conduction occurs by direct contact. For example, when you dip a cold metal spoon into a cup of hot

chocolate, the fast moving particles of the hot chocolate collide with the spoon’s particles and force them to

speed up. If you touch the spoon after it’s been in the hot chocolate, you will feel that it is warm.

The metal spoon conducts heat easily because its particles are free to move about, so it is a conductor. If you

would dip a wooden spoon into the hot chocolate, it wouldn’t be as warm because wood is an insulator; its

particles are more rigid and not able to move as easily, thus conducting heat poorly. Because conduction cannot

happen without particles of matter, it cannot occur in a vacuum.

If you left the hot chocolate out in the open air, the heat would flow into the air and the hot chocolate would

gradually become the same temperature as the air around it. This is an example of thermal equilibrium, in which

heat transfer is stopped due to two masses having the same temperature.

Convection is heat transfer by currents established in liquids or gases. For instance, when a pot of water is heated

on a stove, the water particles at the bottom of the pot become heated by conduction, move faster, and expand.

This hot water rises because of its expansion and low density. The water at the top, being colder and denser,

sinks. It too becomes heated and rises. This rising and falling of particles creates currents that continue until

thermal equilibrium is reached.

Thermal radiation is heat transfer by electromagnetic waves. The Sun is a major source of thermal radiation; its

electromagnetic waves travel through the vacuum of space, hit Earth’s matter, and warm it. For instance, the

sun’s rays will warm your skin if you are standing in a sunny spot. These electromagnetic waves excite the

molecules in your skin, which makes them move faster and cause you to feel warmer.

Thermal radiation depends on color. Black colored objects absorb electromagnetic radiation and turn it into heat

more readily than white or shiny objects.

The Laws of Thermodynamics6(G): Analyze and explain everyday examples that illustrate the laws of thermodynamics,

including the law of conservation of energy and the law of entropy.

Vocabulary

heat: the flow of thermal energy

thermal energy: the kinetic energy of the particles (atoms and molecules) in matter

thermal equilibrium: a state of two systems such that no heat is exchanged between them

law of conservation of energy (first law of thermodynamics): states that although energy can change from one

form to another, it cannot be created nor destroyed

temperature: a measure of the average kinetic energy of the particles in a substance

law of entropy (second law of thermodynamics): states that heat flows spontaneously from hotter objects to

colder (equivalently, heat cannot be transferred from a colder object to a hotter object without work being done

by an outside agent)

Key Concepts

Recall that there are several kinds of energy, such as light, thermal, chemical, and sound. Each of these forms can

be changed into other forms. Nevertheless, no matter how many times energy is transformed, the total amount

of energy remains the same. This principle forms the basis of an important scientific law. The law of conservation

of energy states that although energy can change from one form to another, it cannot be created nor destroyed.

Energy can be transferred from one object to another. For example, an ice cube melts when thermal energy from

the air is transferred to the ice.

Matter is made up of particles (atoms and molecules) that are always in motion. This is called kinetic energy, or

the energy of motion. Thermal energy is the kinetic energy of the particles. Temperature is a measure of the

average kinetic energy of the particles in a substance.

When the motion of the particles that make up a substance changes, the temperature of the substance changes

as well. The faster the particles in a substance move, the higher its temperature. Suppose you have a cup of hot

tea with a temperature of 80°C and a cup of iced tea with a temperature of 10°C. The hot tea has a higher

temperature because the particles in the hot tea are moving faster than those in the cold tea.

Heat is the flow of thermal energy. Heat always flows from an area with a higher temperature to an area with a

lower temperature. Heat will continue to flow in this way until all materials are at the same temperature.

A tube connects the two beakers shown below. The water in the beaker to the left is warmer than the water in

the beaker to the right. Heat will move from the warmer water to the cooler water until all water molecules have

the same amount of energy. The final temperature in both beakers will be the same. At the point when they are

the same temperature and no heat is exchanged between them, they are said to be in thermal equilibrium. What

is often called the Zeroeth Law of Thermodynamics states that if two systems are in thermal equilibrium with a

third system, then they are in thermal equilibrium with each other.

Another important scientific principle, the law of entropy, states that heat cannot be transferred from a colder

object to a hotter object without work being done by an outside agent. Without work being done, heat will

always flow from a warmer object to a cooler object.

Finally, the Third Law of Thermodynamics states that the entropy of a perfect system approaches zero as the

temperature approaches absolute zero. In fact, there is no such thing as a perfect system, so it is impossible to

get to absolute zero.

Oscillatory Motion and Wave Propagation7(A): Examine and describe oscillatory motion and wave propagation in various types of

media.

Vocabulary

wave: a disturbance or vibration that travels

medium: the material through which a wave passes

refraction: the bending of waves as they pass from one material to another

Key Concepts

Waves occur because something is vibrating. For example, a vibrating guitar string creates sound waves.

The sound wave from a guitar string travels through air to get to your ear. Air is called the medium-the material

through which a wave passes.

Sound waves are examples of mechanical waves, meaning they involve the motion of particles of matter. As a

wave passes by, the energy of vibrating molecules, atoms, or other particles causes adjacent particles to vibrate,

and in this way the wave moves forward, or propagates.

As waves move from one medium to another, they change speed because of the change in density. This causes

the waves to bend, a process called refraction.

Electromagnetic (EM) waves are able to move through empty space, and they are the only waves that have this

ability. EM waves propagate as a changing electric field and changing magnetic field that induce one another.

Investigate and Analyze Characteristics of Waves7(B): Investigate and analyze characteristics of waves, including velocity, frequency,

amplitude, and wavelength, and calculate using the relationship between wavespeed,

frequency, and wavelength.

Vocabulary

wave: a disturbance that carries energy outward from a vibrating source

velocity: the distance a wave travels per unit of time; also described as wave speed

frequency: the number of waves that pass a given point per unit of time

amplitude: the maximum amount of displacement from the rest position; in some cases, the effective height of

the wave

wavelength: the distance between two consecutive similar points on a wave, such as from crest to crest or

trough to trough

Key Concepts

Vibration is a back and forth motion. A vibration produces a wave.

Any wave can be described by a set of measurements that include amplitude, wavelength, frequency, and speed.

The greater the amplitude, the more energy the wave carries. When a wave is represented by a diagram, the

amplitude is the distance from the rest position to a crest or trough.

Wavelength is the distance between two consecutive crests, troughs, or other like points on a wave.

Frequency is the number of waves that pass a given point per unit of time. A higher frequency means that more

waves pass a given point in the same time as a wave with a lower frequency.

As explained by the wave equation, the speed of a wave (v ) is directly proportional to wavelength (λ ) and

frequency. (f ): v = fλ

The speed of a wave depends on the medium through which it travels. Because the speed of a wave is constant in

a given medium, wavelength decreases as frequency increases.

Characteristics and Behaviors of Transverse Waves7(C): Compare characteristics and behaviors of transverse waves, including

electromagnetic waves and the electromagnetic spectrum, and characteristics and

behaviors of longitudinal waves, including sound waves.

Vocabulary

wave: a disturbance or variation that travels

oscillate: to move rapidly up and down or forward and back

longitudinal wave: a wave that has oscillations that occur in the same direction as the wave

transverse wave: a wave that has oscillations that are perpendicular to the wave's direction

amplitude: the maximum height or disturbance of a wave

wavelength: the distance between two adjacent crests of a wave

frequency: the number of crests that pass a certain point in a unit of time

electromagnetic waves: oscillations of electric and magnetic fields

electromagnetic spectrum: the range of electromagnetic waves, from long wavelength and low frequency to

short wavelength and high frequency.

interference: the interaction of one wave with another

Key Concepts

Waves are all around you. You see electromagnetic waves and hear sound waves. You might bob up and down

when water waves pass by you in a swimming pool, lake, or ocean.

A wave is a disturbance or variation that travels in both space and time. While the disturbance travels from place

to place with the wave, the particles of matter do not. Send a wave through a rope or spring toy, for example, and

the particles of the rope or spring will oscillate, meaning they move up and down or forward and back, but they

will not move from one end of the rope or spring to the other end.

In a transverse wave, the oscillations are perpendicular to the direction of motion of the wave. Water waves and

waves in a jump rope are examples of transverse waves.

In a longitudinal wave, the particles oscillate in the same direction that the wave is traveling. Rapidly

compressing and stretching a spring toy will form longitudinal waves.

Sound waves are examples of longitudinal waves. They travel as particles move rapidly forward and back. The

particles could be any atom or molecule in a gas, liquid, or solid. Regions where the particles become squeezed

together are called compressions. Regions where they are spread apart are called rarefactions.

The shape and size of a wave are described by the characteristics of amplitude and wavelength. The amplitude of

a wave describes its height. Picture a wave in the ocean. The amplitude is the height of the top of the wave

compared to the surface of the ocean on a calm day. Wavelength is the distance between two identical points on

successive waves.

The frequency of a wave describes how many crests of the wave pass a certain point in a given amount of time.

The wavelength and frequency are inversely related. A long wavelength corresponds to a low frequency; a short

wavelength corresponds to a high frequency.

Sound waves, water waves, and the waves in ropes and spring toys are examples of mechanical waves. These

waves must have a substance to travel through. Sounds will not travel through empty space.

Electromagnetic waves can travel through substances, but they can also travel through empty space.

Electromagnetic waves are oscillations of electric and magnetic fields, and they are examples of transverse

waves. Vibrating electric charges create electromagnetic waves.

The electromagnetic spectrum is the collection of electromagnetic waves of all different wavelengths. A small

part of the electromagnetic spectrum makes up visible light, the light your eye can detect. Other wavelengths of

electromagnetic waves are known by other names, such as X-rays, radio waves, and microwaves.

Waves behave in predictable ways. When waves strike a barrier, they may be reflected from it or absorbed by it;

they may travel through it, or change in other ways. Two waves traveling through the same spot at the same time

will interact with each other in a process called interference.

Behaviors of Waves7(D): Investigate behaviors of waves, including reflection, refraction, diffraction,

interference, resonance, and the Doppler effect.

Vocabulary

reflection: the change in the direction of a wave upon striking a medium so that the wave returns to the medium

from which it originated

refraction: the change in the direction of a wave upon entering a new medium at an angle

diffraction: the bending of waves around a hole or opening in an obstacle

interference: the addition, or superposition, of two waves; may result in an increase or decrease in amplitude

resonance: the tendency of a wave to vibrate at a larger amplitude at some frequencies than at others

frequency: the number of waves that pass a point in a given period of time

pitch: how high or low a sound is; a measure of the frequency

Doppler effect: a perceived increase or decrease in the frequency of a wave due to relative motion between the

source of the wave and an observer

Key Concepts

Mechanical waves involve the motion of matter. Examples include sound waves, water waves, and waves in a

rope. Electromagnetic waves, of which visible light is an example, can travel without matter.

Waves interact with each other and with matter in many different ways, including reflection, refraction,

diffraction, interference, resonance, and the Doppler effect.

Reflection occurs when waves strike a medium and bounce back toward the original medium. For example, light

reflecting from a mirror forms images. Sound reflecting from surfaces forms echoes.

Refraction occurs when waves bend as a result of entering into one medium from another at an angle. The

reason is that the speed of the wave changes in the new medium. When the wave enters the medium an angle,

one side of the wave changes speed before the other. This causes the wave to bend.

Diffraction occurs when waves bend around obstacles or the edges of an opening. The waves spread out as a

result of the interaction.

Interference, or superposition, occurs when waves overlap. During constructive interference, the waves add

together to produce an amplitude greater than that of either wave alone. During destructive interference, the

waves subtract to produce an amplitude less than that of either wave alone.

Resonance describes the phenomenon in which a wave vibrates at a higher-than-normal amplitude at certain

frequencies.

The Doppler effect is responsible for changing the perceived frequency of waves as their source moves relative to

an observer. For sound waves, the change in frequency causes the sound to appear higher or lower. This is why a

police car siren sounds higher as it approaches an observer and lower as it moves away.

Predict Image Formation7(E): Describe and predict image formation as a consequence of reflection from a plane

mirror and refraction through a thin convex lens.

Vocabulary

angle of incidence: the angle between an incoming ray and a line perpendicular to a mirror

angle of reflection: the angle between a reflected ray and a line perpendicular to a mirror

real image: an image formed by converging light rays

focal length: the distance from a lens or mirror to its focus

virtual image: an image formed by diverging light rays

Key Concepts

Mirrors reflect light, meaning they bounce light off their surface. Lenses refract light, meaning that they bend

light that passes through them.

The following is an expression of the law of plane mirrors: An image always appears to be the same distance

behind the mirror as the distance of the object in front of the mirror.

Plane mirrors produce virtual images. Light rays from a virtual image never converge at a single point. For this

reason, virtual images cannot be displayed on a physical surface. The virtual image appears to be behind the

mirror.

The virtual image produced by a plane mirror is a copy of another object. The image, however, is laterally

inverted, or reversed, forming what is commonly called a mirror image.

Plane mirrors follow the law of reflection, which states that the angle of incidence is always equal to the angle of

reflection. Both angles are measured to a normal line, which is perpendicular to the flat mirror.

A convex lens is a thin piece of curved glass that bulges in the middle and narrows to points at either end. When

parallel light rays pass through the lens, they converge at a point on the other side. This point is called the focus.

The distance from the focal point to the center of the lens is called the focal length (f ).

A convex lens often forms real images. Unlike a virtual image, a real image can be projected onto a surface.

The Thin Lens Equation relates object distance (p ) and image distance (q ) to focal length (f ). The equation is:

The magnification M of an object’s image through a lens of focal length f where the object is a distance p from

the lens is given by:

M = ,

If M is positive, the image is virtual and upright. If M is negative, the image is real and inverted.

The Role of Wave Characteristics and Behaviors7(F): Describe the role of wave characteristics and behaviors in medical and industrial

applications.

Vocabulary

ultrasound: sound waves with high frequencies that cannot be heard by the human ear

sonar: a device for locating objects underwater by observing patterns of echoes made by sound waves (originally

an acronym for Sound Navigation And Ranging)

CAT scan: computerized axial tomography scan; a 3-D image made by a computer combining multiple 2D X-ray

images of slices of an object

radar: a device for locating objects by observing patterns of echoes made by radio waves (originally an acronym

for Radio Detection And Ranging)

laser: a device that produces a high-intensity beam of coherent light, in which all the waves are in phase

(originally an acronym for Light Amplification by Stimulated Emission of Radiation)

Key Concepts

All waves, whether sound waves, light waves, or even ocean waves, share certain properties and characteristics.

They are transmitted well in some media, but are reflected off the surface of others. When they move from one

medium to another, their path is often bent through refraction.

These wave properties can be useful in medicine and in industry. In some cases, they replace older, clumsier

methods to get a job done. In others, they make it possible to do something new, such as see inside the human

body without opening it up.

Ultrasound, sound waves with very high frequencies, is used both in medicine to examine the insides of the

human body and in industry to examine the insides of materials. In addition, ultrasound has other uses, including

as a way to clean delicate objects that could not survive being scrubbed.

Sonar is a device carried by many boats that can detect objects in and at the bottom of the water. In sonar, sound

waves are reflected off a submerged object, and are detected and analyzed to determine information about the

object’s size and distance.

In 1895, Wilhelm Röntgen discovered X-rays when he noticed that a detector was glowing even though he d

placed cardboard between the detector and a source of radiation. He soon determined that this kind of radiation

could also pass through skin and flesh. Soon afterward, it came into use as a medical tool that allowed doctors to

observe bones and other features within the body.

Radar is a device used in aviation, law enforcement, meteorology, and other fields to detect objects through the

air. Radio waves are emitted from the transmitter. When the waves strike and object, they are scattered; some

are reflected back to the transmitter. When the reflected signal is detected, it determines the location and size of

the reflecting object. If the object is moving, the signal experiences a change in frequency (a Doppler shift) and

indicates how the object is moving.

Lasers are devices that create a high-intensity beam of coherent light, in which the light waves are all in phase. A

laser beam is able to deliver more energy over longer distances than an ordinary light beam. They are used in

communication, medicine, and many other kinds of technology.

The Photoelectric Effect and the Dual Nature of Light8(A): Describe the photoelectric effect and the dual nature of light.

Vocabulary

photoelectric effect: the phenomenon in which matter emits electrons as a result of absorbing electromagnetic

radiation

electromagnetic radiation: energy carried by electromagnetic waves, including radio waves, microwaves,

infrared light, visible light, ultraviolet light, X-rays, and gamma rays

spectrum: a distribution of electromagnetic radiation across a range of frequencies

photon: a quantum of electromagnetic radiation; has neither mass (at rest) nor electric charge

dual nature of light: a description of light as both a particle and a wave, necessary because light appears to have

two sets of properties

Key Concepts

When light shines upon a metallic surface, the surface may emit electrons. This phenomenon is known as the

photoelectric effect. The electrons are sometimes described as photoelectrons.

The electrons emitted as a result of the photoelectric effect can be made to produce an electric current. The

energy of this current can be measured and used to calculate the maximum kinetic energy of the electrons.

Many observations of the photoelectric effect cannot be explained by the idea that light travels only as a wave.

The photoelectric effect does not occur below a certain frequency, the intensity of the light does not affect the

maximum kinetic energy of the emitted electrons, and there is no delay between when the light is shone and the

emission of electrons.

Building on the research of many scientists, Albert Einstein proposed a theory to explain the photoelectric effect.

He proposed that electromagnetic radiation is packaged in small bundles, now known as photons. A single

photon can transfer energy to instantaneously eject a single electron from a metal.

Einstein showed that if a photon does not have a minimal amount of energy, no electrons will be emitted. The

energy depends on the frequency of light rather than the intensity. Increasing the intensity of light will increase

the emission of electrons but will not increase their kinetic energy.

The photoelectric effect can be explained only by the particle nature of light, involving photons. Other

phenomena, such as diffraction, can be explained only by the wave nature of light. This has led scientists to

accept the dual nature of light, and that both particles and waves are necessary to explain its properties.

Emission Spectra8(B): Compare and explain the emission spectra produced by various atoms.

Vocabulary

continuous spectrum: a continuous band of various colors produced by projecting white light through a prism.

Each section of color represents the frequency of an electromagnetic wave.

spectroscope: an instrument used to separate the light emitted from a hot gas into its constituent frequencies

discrete spectrum: a series of discrete colored lines produced when light emitted from a hot gas is separated by a

spectroscope. Each colored line represents the frequency of an electromagnetic wave.

spectral line: an individual line of color that is part of a discrete spectrum and represents the frequency of an

electromagnetic wave

diffraction grating: a small lens with tiny slits that allow light to disperse in such a way that the electromagnetic

waves interfere with one another. This interference causes reinforcement and cancellation such that the

reinforcement produces a particular color (frequency) and the cancellation results in the absence of color (black).

Key Concepts

An example of a continuous spectrum is a rainbow produced in the sky during or after a rainstorm when white

light is dispersed by droplets of water vapor. That same rainbow can be reproduced when white light is projected

through a prism. Each color in the rainbow represents a particular electromagnetic wavelength and

corresponding wave frequency. For instance, red light has the longest wavelength, ranging from 600 to 700 nm;

its frequency is the smallest, at 4.3x1014

Hz. Conversely, violet light has a wavelength of about 400 nm and a

frequency of 7.5x1014

Hz.

Every element has its own particular color when it is made to emit light. This works best with elements in the

gaseous state, when the atoms are far enough apart such that their particular vibrations do not interfere with

one another, as would be the case in the solid or liquid state. The light from a gaseous glowing element can be

separated through an instrument called a spectroscope. The dispersed light from a spectroscope is arranged in a

discrete spectrum. A discrete spectrum, or a discrete emission spectrum , is different from a continuous spectrum

in that the colors are not arranged in a continuous band but in a series of individual lines. Every element has its

own discrete spectrum, which acts as a fingerprint. This is how scientists can tell what elements constitute an

unknown substance.

Each spectral line in a discrete spectrum corresponds to a particular frequency or color of light. Each element has

a unique discrete spectrum with a unique sequence of spectral lines because each element has its own distinct

configuration of electrons that emit distinct frequencies of light when they are excited and change energy levels.

The diffraction grating is the part in the spectroscope that produces the discrete spectrum. It does this by wave

interference. Were you to observe waves at a sea wall, you would notice how waves coming in interfere with the

waves bouncing off the wall. If two waves interfere with each other such that their wave crests are

superimposed, the result is a higher wave. If one wave’s crest is superimposed on another wave’s trough, the

wave is cancelled. A diffraction grating works by light wave interference in that waves are reinforced and

cancelled. The reinforced waves produce a spectral line and the cancelled waves show no color, or appear black.

The Significance of Mass-Energy Equivalence8(C): Describe the significance of mass-energy equivalence and apply it in explanations of

phenomena such as nuclear stability, fission, and fusion.

Vocabulary

nuclear reactions: changes that occur within an atomic nucleus

nuclear fission: the splitting of a large atomic nucleus into smaller nuclei

nuclear fusion: the joining of two small atomic nuclei into a larger nucleus, accompanied by the release of a

tremendous amount of energy

Key Concepts

A nuclear reaction involves the nucleus of an atom or the nuclei of two or more atoms. During most nuclear

reactions, the mass of the reactants is greater than the mass of the products. The “lost” mass is converted into

large amounts of energy.

Nuclear power plants produce electrical energy from nuclear fission. As shown in the illustration, nuclear fission

is a reaction in which some of the energy stored in the nucleus of an atom is released by splitting the atom into

two smaller nuclei.

A safety risk of nuclear fission is that it involves radiation, which must be contained. The release of radiation into

the environment can result from a nuclear accident or from improperly stored radioactive wastes. The radiation

is extremely harmful to living cells.

In nuclear fusion, light nuclei are combined to make a heavier nucleus. The energy of the Sun is derived from

nuclear fusion reactions. In these reactions, hydrogen nuclei combine to form helium nuclei. In the process, huge

amounts of energy are given off.

Atomic, Nuclear and Quantum Phenomena8(D): Give examples of applications of atomic and nuclear phenomena such as radiation

therapy, diagnostic imaging, and nuclear power and examples of applications of quantum

phenomena such as digital cameras.

Vocabulary

nuclear phenomena: events that result from changes within the nucleus of an atom

atomic phenomena: events that result from changes to the atom as a whole

discrete: values that are distinct, separate, or finite

continuous: values that exist at every point within a given range

quantum: the smallest unit used to measure a quantity, such as energy

photoelectric effect: the phenomenon in which matter emits electrons as a result of absorbing electromagnetic

radiation

electromagnetic radiation: energy carried by electromagnetic waves that take the form of visible light,

microwaves, X-rays, ultraviolet light, or gamma rays

nuclear fusion: the process through which light atomic nuclei combine to form a heavier nucleus

nuclear fission: the process through which a heavy atomic nucleus breaks apart to form lighter nuclei

Key Concepts

Atoms consist of smaller particles. Two of those particles, neutrons and protons, are located in the center, or

nucleus, of an atom. Changes to the nucleus produce phenomena that have many important applications,

including radiation therapy, diagnostic imaging, and nuclear power.

Radiation therapy is the medical use of ionizing radiation to treat disease. Diagnostic imaging consists of

technologies that make it possible to form images of interior regions of the human body. Nuclear power is the

release of energy through the processes of nuclear fission or nuclear fusion.

Quantum phenomena have specific applications, such as the development of digital cameras. The term quantum

is related to quantity. Quantum phenomena, such as the energy of an electron, exist only in discrete values rather

than across a continuous range