Conservation

of Energy

Essential Standard 3.1Understand types of energy,

conservation of energy, and

energy transfer.

Learning Objective 3.1.2

Explain the law of conservation of energy in a

mechanical system in terms of kinetic energy,

potential energy, and heat.

I Can StatementsAt the end of this lesson, you should be

able to say, with confidence:

• I can distinguish between kinetic and

potential energy

• I can calculate kinetic energy

• I can calculate gravitational potential energy

• I can explain how the Law of Conservation

of Energy applies to everyday transfers of

energy

EnergyEnergy is the ability to cause change and any change

that does takes place requires energy.

Water falling at a

hydroelectric dam has a

lot of energy because it

has the ability to cause

a lot of change to

anything it falls upon or

moves downstream.

All energy can be put into two categories: kinetic

energy and potential energy.

Kinetic EnergyKinetic energy is energy in motion or when energy is

actually being used.

The falling water is

an example of

kinetic energy.

The amount of kinetic

energy present is based

on mass and velocity.

A large amount of water flowing at a fast speed will be

able to cause a lot more change than a small amount of

water flowing very slowly.

Calculating Kinetic Energy

KE = ½mv2

Units

Kinetic Energy (KE) = J

Mass (m) = kg

Velocity (v) = m/s

Joules (J)

The unit for energy is joules,

named after the English scientist,

James Prescott Joules.

Joules was the first to discover that all forms of energy

are basically the same and can be changed from one

form into another.

1 joule (J) = the energy required to

raise 1 liter of water, 1 meter high,

within one second.

Calculating Kinetic EnergyA jogger whose mass is 60 kg is moving at a speed

of 3 m/s. What is the jogger’s Kinetic energy?

m = 60 kg v = 3 m/s

KE = 1/2mv2 = (60)(32) = 270 J

2

Potential EnergyPotential energy is stored energy and has the potential

of causing change when it is used.

The water in the

reservoir has

potential energy due

to it’s height.

The amount of potential energy the water in the

reservoir has depends upon its mass, height, and its

acceleration due to gravity.

Calculating Potential Energy

PEg = mgh

Units

Gravitational Potential Energy (PEg) = J

Mass (m) = kg

Gravity (g) = m/s/s (9.8 m/s/s)

Height (h) = m

What is the gravitational potential energy of a 7 kg box

that is 4 m above the ground?

Calculating Potential Energy

m = 7 kg g = 9.8 m/s h = 4 m

PEg = (7)(9.8)(4) = 274 J

Energy and MoneyEnergy is a lot like money. Money can be spent or used,

like kinetic energy, or it can be stored or saved, like

potential energy.

Money comes in many different

forms and all of those forms can

be saved or spent.

Energy also comes in many

different forms and be stored or

used in many different ways.

1. Elastic Potential Energy

2. Chemical Potential Energy

3. Electrical Potential Energy

4. Nuclear Potential Energy

5. Gravitational Potential Energy

Types of Potential EnergyMost types of potential energy can be put into six

main categories:

Elastic Potential Energy is energy stored by

things that stretch

Elastic Potential Energy

Chemical Potential Energy is energy stored in the

chemical bonds between atoms.

Chemical Potential Energy

Electrical Potential Energy is energy stored in an

electrical charge.

Electric Potential Energy

Nuclear Potential Energy is energy stored in the

nuclei of atoms

Nuclear Potential Energy

Gravitational Potential Energy is energy stored in

things that are above ground level

Gravitational Potential Energy

Energy ConversionsEnergy conversions occur when energy changes

from one form to another.

Electrical

Energy

Light

Energy

Heat

Energy

Law of Conservation of EnergyEnergy cannot be created or destroyed, only

transferred.

A ball rolling down an inclined plane cannot travel higher than the original height on

another inclined plane.

Law of Conservation of Energy

The ball starts out with high gravitational potential energy PEg.

As the ball travels down the slope, it

loses PEg but gains kinetic energy, KE, as it increases in

speed.

As the ball travels up the other slope, it loses KE as it slows down. But, it gains PEg as it gains height.

High PEg High PEg

Low PEg

Low KE Low KE

High KE

Law of Conservation of Energy

During the balls motion, energy is conserved through each transfer of energy.

Total Initial Energy = Total Final Energy

PE = 30JPE = 30J

PE = 0J

KE = 0JKE = 0J

KE = 30J

30J 30J

Law of Conservation of Energy

In this example, friction and air resistance was ignored.

The heat energy escapes into the surrounding air, and while not destroyed, cannot be used by the

marble. So, the marble actually would never travel as high as the original height.

In reality, friction and air

resistance would transfer some of the energy into heat energy.

Law of Conservation of EnergyThis is how roller coasters work.

A machine pulls the cart to the top of the first hill. After that, the cart goes through a series of energy transfers, until it finally comes to a stop due to loss

of heat energy due to friction.

The End