Energy is used everyday… Can you think of any examples?

Energy can take many forms

• radiant • electrical• chemical• thermal

• nuclear

• sun

• power lines

• gas, food• energy that comes from

the particles that make up matter

• fission (reactor)

Traditionally, energy is defined as…

• the ability to do work or to cause something to move.

• However, energy involves change, therefore a better definition is:

• ENERGY = the ability to cause change.

• The basic unit of energy is the Joule (J).

• The equivalent units are : N*m

Kinetic

Potential

Kinetic Energy

• Kinetic energy is energy in the form of motion.

• The amount of kinetic energy in a moving object depends on its mass and velocity

• The formula for kinetic energy is :• KE = ½ mv2

Kinetic EnergyKinetic Energyenergy of motion

All moving objects thatAll moving objects thathave mass have kinetic energy.have mass have kinetic energy.

KE = 1/2 mvKE = 1/2 mv22

mm - mass of the object in - mass of the object in kgkgvv - speed of the object in - speed of the object in m/sm/sKEKE - the kinetic energy in - the kinetic energy in JJ

Which of each pair has more kinetic energy?

• a bus traveling at 65 mph?

• a bus traveling at 65 mph

• car traveling at 65 mph

• bus traveling at 40 mph

Potential Energy

• Potential Energy is stored energy.• The amount of potential energy in a sample of

matter depends on its position or condition.• Potential energy due to height above Earth’s

surface is called gravitational potential energy.

• Formula: PE (due to gravity) = mgh

9.8m/s2

Potential EnergyPotential Energyenergy of position or conditionenergy of position or condition

gravitational potential energygravitational potential energy

PEPEgg = mgh = mgh mm - mass of object in - mass of object in kg kg gg - acceleration of gravity in - acceleration of gravity in m/sm/s22

h h - height of object, in - height of object, in mm,, from some arbitrary reference pointfrom some arbitrary reference pointPE PE – gravitational potential energy in – gravitational potential energy in JJ

Circle which of each pair has more potential energy:

• boy sitting in a tree 12 ft. in the air.

• squirrel sitting in a tree 30 feet in the air

• squirrel sitting in a tree 12 ft. in the air

• squirrel sitting in a tree 12 ft in the air.

•Decide whether each slide is an example of potential or kinetic energy.

•Click on your answer to see if you are correct.

Click your mouse to begin.

Whenever you see this picture, you will need to write the answer in your journal.

The Ball

PotentialEnergy

KineticEnergy

PotentialEnergy

KineticEnergy

PotentialEnergy

KineticEnergy

PotentialEnergy

KineticEnergy

PotentialEnergy

KineticEnergy

Conservation of Energy

1. The law of conservation of energy states that energy may change form, but it cannot be created or destroyed under ordinary conditions.

2. Mechanical Energy is the total amount of potential and kinetic energy in a system.

3. The amount of kinetic and potential energy in a moving swing is always changing, whereas the amount of mechanical energy is constant.

continued…

4. Let’s look at the case of a bouncing ball.

Energy changes from potential energy at the top of the bounce to kinetic energy when it hits the floor , and back to potential energy as it goes back up. During this time, the mechanical energy of the ball stays constant.

5. Fill in the diagram of a bouncing ball with the correct response below.

greatest potential energy, no kinetic energy

greatest kinetic energy, no potential energy

greatest kinetic energy, no potential energy

kinetic energy increasing, potential energy decreasing

kinetic energy decreasing, potential energy increasing

6a. The ball in the previous diagram will eventually stop bouncing. Why?

• Because gravity will slow the ball down .6b. As the ball stops bouncing, is energy lost?

Explain.

• No, because the kinetic energy eventually changes to potential energy, but energy is not lost.

7a. In this picture, where does the roller coaster have the most potential energy?

• At the top because it has an instantaneous speed of 0 m/s.

7b. Where does it have the most kinetic energy?

• At the bottom because it’s where it is going the fastest.

References

1.http://www.hehs.d211.org/people/ruthek/PowerPoints/Conservation%20of%20Energy%2C%20Energy%2C%20and%20Work.

ppt2. faculty.physics.tamu.edu/ford/PowerPoints/WorkEnergyPower.ppt

3. http://www.hazelwood.k12.mo.us/~cdavis01/map2000/5th/eric03.ppt