Chapter 4:Chapter 4:EnergyEnergy

Nature of Energy

• Energy is all around you!– You can hear energy as sound.– You can see energy as light.– And you can feel it as wind.

Nature of Energy

• Energy is involved when:– a bird flies.– a bomb explodes.– rain falls from the sky.– electricity flows in a

wire.

Nature of Energy

Living organisms need energy for growth and movement.

Nature of Energy

What is energy that it can be involved in so many different activities?

Energy

Energy can be defined as the ability to cause change.

Energy Unit of Measure

ALL forms of energy is measured in units called joules.

Scientists refer to 2 types of energy

Kinetic Energy

Potential Energy

What is kinetic energy?

Kinetic Energy

The energy of motion is called kinetic energy.

Kinetic Energy

Kinetic energy depends on both mass and velocity.

The faster an object moves, the more kinetic energy it has.

The greater the mass of a moving object, the more kinetic energy it has.

Let’s Look…..

The vehicles below are traveling at the same velocity of 100 km/h. Do they have the same amount of kinetic energy? Why? Why not?

Answer

No, the kinetic energy is different for each vehicle. The truck has a GREATER mass than the motorcycle, so the truck has GREATER kinetic energy.

Formula for Kinetic Energy

K.E. = mass x velocity2

2

K.E. = m X v2

2

What has a greater affect of kinetic energy, mass or velocity? Why?

The velocity does because its value is squared!

Let’s Practice..

Calculate the kinetic energy of a 3 kg rock that rolls down the hill with a velocity of 2 m/s.

K.E. = m X v2

2

Did you get……Calculate the kinetic energy of a 3 kg rock

that rolls down the hill with a velocity of 2 m/s.

K.E. = 3 X 22

2

K.E. = 6 Joules

Quiz Time!

Show me what you have learned so far by answering the 4 questions that follow….

Question 1

Which has more kinetic energy, a large dog sitting on a sidewalk or a small cat running down the street?

a. The large dogb. The small catc. Both have the same kinetic energyd. Need more information to answer

Question 2

To what property of an object is kinetic energy directly related?

a. Volumeb. Heightc. Positiond. Mass

Question 3

Observe the figure below. Which motorcycle has more kinetic energy? Assuming that the motorcycles have the same mass.

a. Motorcycle Ab. Motorcycle Bc. Need more information

A B

Question 4

Elastic potential energy is measured in ________.

a. Kilograms (kg)b. Newtons (N)c. Joules (J)d. Meters per second (m/s)

What is potential energy?

Potential Energy

Potential energy is stored energy due to position.

Motionless objects have potential energy!

3 Types of Potential Energy

Elastic Potential Energy

Chemical Potential Energy

Gravitational Potential Energy

Elastic potential energy- energy stored by something that can stretch or compress

Chemical potential energy- energy stored in chemical bonds

Gravitational Potential Energy: energy stored by objects ABOVE Earth’s surface

Apple

Gravitational Potential Energy

“The bigger they are the harder they fall” is not just a saying.

It’s true!

Objects with MORE mass have greater Gravitational potential energy (G.P.E.)

Gravitational Potential Energy

G.P.E. depends on 3 things:

1. Mass of the object2. Acceleration due to gravity = 9.8 m/s2

3. Height of the object

Formula for G.P.E.

G.P.E. = mass X 9.8 m/s2 X height

G.P.E = m X 9.8 m/s2 X h

Let’s Practice..What is the GPE of a 65 kg pole

vaulter that is 15 m in the air?

G.P.E = m X 9.8 m/s2 X h

Did you get……

What is the GPE of a 65 kg pole vaulter that is 15 m in the air?

G.P.E = 65 X 9.8 X 15

G.P.E. = 9555 J

Quiz Time!

Show me what you have learned so far by answering the 4 questions that follow….

Question 1

The gravitational potential energy of an object depends on which of the following?

a. Velocity and heightb. Velocity and weightc. Weight and heightd. Weight and acceleration

Question 2

Which vase has more gravitational potential energy?

a. Vase Ab. Vase Bc. Can not determined. Vase A and B have the same

GPE

A

B

Question 3

Green plants store energy from the Sun in what form?

a. Light energyb. Elastic potentialc. Gravitational potential

energyd. Chemical potential

Question 4

Observe the figure on the right. At which point would the roller coaster have the MOST potential energy?

a. Point Ab. Point Bc. Point C

A

B

C

Conservation of Energy

Energy is most noticeable when it changes from one form to another!

Think about it…..

Would you….

Would you think that a book on top of a bookshelf as having much to do with energy?

Well, probably not until it fell, right?

Energy Tranforms…..

Energy transforms from one form of energy to another form of energy.

Let’s consider……The electrical energy from a light bulb is transformed into what types of energy? Electrical Energy

Light Energy

Thermal (Heat) Energy

Energy Transforms………..Potential Energy Kinetic Energy

Ball slows down

Ball speeds up

Kinetic vs. Potential Energy

At the point of maximum potential energy, the car has minimum kinetic energy.

Kinetic-Potential Energy Conversion

Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride.

The Law of Conservation of Energy

Energy can not be created or destroyed it can only be converted from one form of energy to another.

The total amount of energy in the universe remains constant!

Friction converts some mechanical energy to thermal (heat) energy.

Rub your hands together. Feel it!

Mechanical Energy

Mechanical Energy – is the total amount of P.E. and K.E. in a system

M.E. = Total P.E. + Total K.E.

Nuclear Fission =

nuclei split apart

(fission=division)

Nuclear Fusion =

nuclei combine

(fusion FUSE)

Mass is converted to energy in the processes of fission and fusion.

The food calorie (C) is a unit used by nutritionists to measure how much energy you get from various foods.

1 calorie = 4.184 joulesKilocalorie = Calorie

Quiz Time!

Show me what you have learned so far by answering the 4 questions that follow….

Question 1

What energy transformations occur when a lump of clay is dropped?

a. GPE KE thermal energyb. KE chem PE thermal energyc. KE GPE thermal energyd. GPE KE elastic PE

Question 2

Suppose a juggler is juggling oranges. At an orange’s highest point, what form of energy does it have?

a. Mostly potential energyb. Mostly kinetic energyc. No potential or kinetic energyd. Equal amounts of both

Question 3

Which idea is central to the law of conservation of energy?

a. Friction produces thermal energyb. People must conserve energyc. The total amount of energy is constantd. Energy is the ability to cause change

Question 4

Friction frequently causes some of an object’s mechanical energy to be changed to which of the following forms?

a. Thermal energyb. Nuclear energyc. Gravitational potential energyd. Chemical potential energy

The End

Be ready for TEST!