8TH GRADE ENERGY

UNIT

What is ENERGY?

• ENERGY – The ability to do work or create a change.– Law of Conservation: Energy is

neither created nor destroyed…only changes form & position.

• WORK – Force exerted on an object (matter) that causes it to move…energy is needed!

• W : force x distance moved = ____joules

Video clip

Categories of Energy

Kinetic Energy Potential EnergySound Gravitational (GPE)

Mechanical (objects move) Mechanical (objects in position…ready)

Radiant (electromagnetic spectrum)

Nuclear (energy stored in nucleus)

Thermal (heat) Chemical (stored in particles)

Electrical

Kinetic Energy

• Kinetic Energy (KE) – The energy of an object due to its motion.

• How to find kinetic energy:KE: Mass of object x Velocity ² / 2

=____Joules

Potential Energy / GPE

• Potential Energy – Energy that is stored and held in readiness.

– Gravitational Potential Energy (GPE) – Potential energy that depends on the height of object causing gravity to affect it more.

• GPE: height of object (h) x mass (m) = ______ Joules (J)

Video clip

Work

LAB Reviews• Transfer of energy means to pass

energy from one place to another (one object to another) without changing forms.

• Transformation of energy means that energy has changed from one form to another.

Ball & Ramp

Less GPE = less speed = less KE

More GPE = higher speed = more KE

GPEKE

GPE

KE

GPEKE

GPE

KE

Passing energy along…

The KE from the ball was transferred (passed) to the Styrofoam cup…the ball lost KE and the cup gained KE…Work was done!! (Cup absorbed the KE from ball)

Transfer & Transformation

GPE KE

KEGPE

TRANSFORMATIONTRANSFORMATION

TRANSFERTRANSFER

•Air particles

•Surface & cup

Pendulum demonstration

GPEKE

GPEKE

GPEKE

GPE

KE

GPEKE

GPEKE

GPEKE

• Transformation of Energy GPE KE GPE again…

Energy transfer (absorbed) – activity #5

• How does type of surface affect energy transfer?

– Surfaces whose particles are tightly packed can only absorb a little bit of energy at a time (many bounces)

– Surfaces whose particles are loosely packed can absorb more energy at a time (less bounces)

Bouncing Ball

Flooraccepts less energy at atime… more dense

Cardboard acceptsmore energy at a time…less dense

GPEKE

GPE

KE

Transformation of Energy examples…

• EngineEngine = chemical kinetic

• HeaterHeater = chemical heat

• SolarSolar = radiant electrical

• BatteryBattery = chemical electrical

• FoodFood = chemical heat / KE

• PhotosynthesisPhotosynthesis = radiant chemical

Energy Chains

• Energy can transfer & transform.• This reaction forms “energy chains”,

where we can map out energy’s change. We usually start with the Sun

What becomes of KE?

• What becomes of KE after it transfers?

• When KE transfers from one place to another through physical contact, it not only gives the energy of motion, but also transforms into heat energy!

• Friction – A resistance between 2 objects, usually a sliding motion.

Force

• In order for KE to be transferred or transformed, there must be something making “matter” accelerate or change direction.

• Force = is a push or pull that causes a substance with mass (takes up space) to accelerate in a certain direction.

» Force can change amount of friction!!!

Activity #7Force (pulling)

Force of Friction

KE can be transferred and some of it transforms into heat energy. Friction transfers energy…

• more force = more friction = more KE transfer = more heat energy!!

Thermal & Heat Energy If all matter has KE, then it must possess Thermal Energy!!

Phases of Matter

Phase Change Particle Model

Low KE medium KE High KE

Temperature

• Temperature measures the “average KE” (motion) of particles that make up a substance.– Thermometers are the instruments

we use.

– Liquid thermometers (water, alcohol, &

liquid mercury) work by thermal expansion & contraction.

Different Temperature Scales

Absolute Zero K: Point at which all motion has stopped…no energy!!

What is Thermal Energy?

• The TOTAL energy of all the particles in a substance (matter).

• 3 Factors to find thermal energy:1. Must know the avg. KE (temp.)2. Must know how much (mass or volume)3. Must know the arrangement of particles (solid,

liquid, or gas) which one has

A more thermal B energy?

100 ml of water 125 ml of waterat 30 C at 30 C

What is heat ?

• Heat is the actual transfer of Thermal Energy. When Thermal Energy is transferred from one place to another, we call it “heat.”

Thermal energy gets transferred to the air, then to the person (HEAT).

Fire has LOTS of Thermal Energy

Thermal Expansion & Contraction

• In physics, thermal expansion is the tendency of matter to change in length or volume in response to a change in temperature. When a substance is heated, its particles move around more vigorously and by doing so generally maintain a greater average separation. This requires more space!!

1st Law of Thermodynamics

• States that energy is neither created nor destroyed…it is just passed along and/or transformed (conservation of energyconservation of energy).

– All the energy that is in the universe right now can only change position or form!

2nd Law of Thermodynamics

• Thermal energy flows (heat) spontaneously from a warmer body to a cooler one.

• One cannot transfer or transform heat completely into useful work, some of the energy becomes unusable…

• Every isolated system becomes disordered in time (entropy).

Phase change names

Phase change graph

3 ways “heat energy” moves…

1. CONDUCTION

2. CONVECTION

3. RADIATION

CONDUCTION

• Process where heat energy is transferred by physical contact through a substance. Particles of a substance have to touch each other to pass heat from warmer to cooler.

Warmer area,Lots of KE

Cooler area,gaining KE…warming up

Collision of particles

Conductor vs. Insulator

• A good conductor is a substance that allows heat to transfer through it easily.

• A bad conductor (Insulator) is a substance that does NOT allow heat to transfer very well toward the cooler area.

InsulatorsFire gear: keeps heat from skin exposure

Space suit keeps heat from sun minimal

Ice actually slows the transfer of heat from inside to outside

Investigation #11Conduction

• Purpose / Question:– To observe how HEAT energy moves

by conduction.

– Do some substances allow heat energy to conduct better than others?

• Background Knowledge:– Look at the demonstration. Which

spoon would you pick up first?

metal or plastic

– Why?

• Hypothesis:– Rods with more mass will (allow / not

allow) heat to transfer well.

– Rods with less mass will (allow / not allow) heat to transfer well.

• ExperimentMaterials:

– Solid rods (aluminum, steel, brass, glass)– Hollow rods (brass & aluminum) – 2 clothes pins– Candles– Large paper– 2 blocks– Timer – Safety goggles!!!

Procedure1. Find the mass of each type of rod (g) and

record in data table.2. Be very precise in measurements!

Metal Rod

• 3. Take one rod (save glass rod for last) and line it up on template.

• 4. Using the marker, place a line where the 3 globs of wax will be resting & flame line.– Flame line = 3inches from edge.– Wax 1 = 2 inches from edge.– Wax 2 = 1 inch from edge.– Wax 3 = very edge of rod.

Wax 3Wax 2Wax 1FLAME

ROD

• 5. Light big candle and allow wax to run off and drip onto the designated 3 areas for wax globs (edge, 1in., and 2 in.)

• 6. Use the clothes pins to suspend the bar above the surface.

• 7. stack 2 blocks & place a lit candle directly under the inner-most marked line on bar.

• 8. Once flame hits the bar, start timing.• 9. You are looking for how long it takes

each glob of wax to start melting. • 10. Write observation times in data

table.

Final set-up for Investigation #11

CONVECTION

• Represents the transfer of heat by circulation or movement of the hot particles to cooler areas. Warmer, less dense fluids rise, while cooler, more dense fluids fall and replace.

Warm, less dense air rises…cools Cool, more dense

air falls…warms again

Video clip

RADIATION

• Energy that travels through the emptiness of space (does not need particles to transfer). Travels by electromagnetic waves away from a heat source.

What is Radiation?

• All energy, typically from a light source like a star (Sun) that transfers energy without a medium (but can transfer some through liquids & gases)

– A medium refers to anything made up of particles (solids, liquids, gases)

Color affects absorption

Black bodies: Summer clothing:  white reflects radiant energy better than black.

 Until equilibrium is reached, white  stripes on roads are at a lower  temperature than unpainted asphalt.

 Wrap an ice-cube in black cloth and another in aluminum foil and  place both in the sunshine.  What will happen?

What are Waves?

• A wave is a disturbance when energy is transferred through a ‘medium’. – Medium = (solid, liquid, gas, electric &

magnetic fields)• A wave is created when energy moves

through a “medium” causing it to become displaced.– Sometimes permanently – Sometimes temporarily

2 Categories of Waves• 1.) Mechanical Waves – Energy that

requires a “medium” to transfer.

• 2.) Electromagnetic Waves (EM) – Energy that does NOT need a “medium” to transfer

Sound is just vibrations of air particles hitting each other.

Earthquakes send enormous amounts of energy through matter.

Heat & light

Types of Waves1. Transverse Wave – Waves that move

the medium at “right angles” to the direction in which the energy is traveling.

The medium Medium being disturbed by the energy

Direction of energy flow

Types of Waves cont…

2. Longitudinal Waves – Waves that moves the particles of the medium “parallel” to the direction the energy is traveling. (SOUND)

Type of Waves cont…

3. Surface Waves – Combinations of transverse & longitudinal waves, causing a circular motion of particles. This occurs between 2 mediums (water & air).

Parts of a wave…

• Amplitude - maximum displacement from the undisturbed position of the medium or electromagnetic field.

• Wavelength - The wavelength of a wave is the distance between any two adjacent corresponding locations on the wave train

• Frequency - How many waves are made per time interval…usually # per sec. (Hz)

• Crest & Trough - The section of the wave that rises above the undisturbed position is called the crest. That section which lies below the undisturbed position is called the trough.

Parts of a Transverse WaveFrequency (1second time = Hz)

Wavelength (λ)

amplitude

Crest

Trough

Medium

Parts of a Longitudinal Wave

Doppler Effect

• The apparent change in Frequency as the wave source moves toward or away from the listener. Car is source

making noise (moving)Frequency

is lower (low pitch) Frequency

is higher (high pitch)

Click for visual Click for example

Supersonic (breaking sound barrier)

• When a wave source catches up and passes the outgoing waves of energy. Sound barrier

Click for video example

Electromagnetic Radiation(EM Waves)

Energy that comes from our star (the Sun) & travels through the emptiness of space.

How does energy travel through emptiness of space???

• “Space particles” known as photons carry energy through space, but not matter.

• Some photons carry lots of energy (gamma rays)

• Some photons carry little energy (radio waves)

What are EM radiation waves?

– Space is mostly made of magnetic & electric fields

– EM waves are transverse waves that have electric & magnetic properties

– When energy transfers, it disturbs the electric & magnetic fields.

How it travelsDifferent energy from the Sun all travel the same speed through space (186,000 miles/sec)

What changes is the wavelength and frequency.

Energy with longer wavelengths = smaller frequency

Energy with shorter wavelengths = higher frequency

Types of EM Radiation

Visible Light

The part of the Electromagnetic Spectrum (frequency) that our eyes can detect.

Properties of Visible Light

Shorter wavelength = higher frequency

Longer wavelength = lower frequency

Properties of Visible LightWhen light from our Sun becomes bent (Refraction) at different angles, we see the “spectrum of light” or sometimes an optical illusion.

Red

Orange

Yellow

Green

Blue

Indigo

Violet

Light: Waves of energy, particles, or both???

Light has NO mass…can pass through substances without increasing mass…acts like a EM wave.

Light sometimes acts as a particle where it reflects or even moves substances…acts like a particle. Light particle is a PHOTON

flashlight

flashlight

Photon carries the energy

Visible Light Hitting an Object

1. Reflect

2. Transmit

3. Absorb

Reflection• Regular Reflection – When parallel

rays of light hit a smooth surface and all the rays bounce off the same direction & angle

bounces

Reflection cont…• Diffuse Reflection – When parallel rays

of light hit a bumpy or uneven surface they bounce off at different angles & direction.

Transmission

• To allow light energy to pass through a substance.

TRANSPARENT (clear)

TRANSLUCENT (not clear)

Absorption

• When visible light is absorbed, it is known as the “absence” of light…which is black.

White

All absorbedBlack