Energy of Motion

Physics of Fun (26min)

Energy

• Any change in motion requires – Energy.– Work is done when a change occurs.• Work can’t be done without energy!

• When an object or organism does work on another object, some of its energy is transferred to that object.– Law of Conservation of Energy – Energy cannot be

created nor destroyed but is transferred from one object to another.

Types of Energy• 2 Types of Energy:

1. Potential Energy (PE) – stored energyi. Associated with position – increase an object’s height, increase the

amount of PE it has.a. A roller coaster at the top of the peakb. An arrow in a bow that is drawn backc. The food you are about to eat

2. Kinetic Energy (KE) – energy of motioni. Depends on the objects mass and velocity

a. Double an object’s mass = double it’s KEb. Double an object’s velocity = quadruple it’s KE

a. An arrow flyingb. A bus movingc. A rock rolling down a hill

Identifying Potential & Kinetic Energy

1. What type of energy did the ball have as the girl held it at the top of the cliff?

2. What type of energy did the ball have after she let the ball go?

3. When would kinetic energy be the greatest?

Potential Energy

Kinetic Energy

Just prior to hitting the ground

Identifying Potential & Kinetic Energy1. At what location(s) would the

biker have kinetic energy?2. What type of acceleration

would the biker have at A?

3. At what location(s) would the biker have potential energy?

4. Where would the biker’s kinetic energy be the greatest? Why?

A & C

B

C – greater velocity

A

B

C

Negative Acceleration – slowing down

Potential & Kinetic Energy• Would Student A or

Student B have the least Potential Energy?

• Would Student A or Student B have the greater velocity?

• Would Student A or Student B have the greater Kinetic Energy?

Student A – lower height

Student B – longer fall

Student B – greater velocity = greater KE

Potential vs. Kinetic• Kinetic Energy can NEVER be greater

than Potential Energy.– Energy is lost due to friction and/or

gravity.• Bounce a ball, the second bounce will be

shorter than the starting height of the first bounce.– Gravity pulls the ball down– Air resistance (friction) slows the ball down

as it falls.

– A roller coaster will never have a second height higher than the initial drop off.• Friction turns energy into heat and slows it

down.

Potential vs. Kinetic Energy• At what location does the ball

have the greatest potential energy?

• At what location does the ball have the greatest kinetic energy?

• What factors affect the bounce at D and make it so it will not reach the same height as A again?

A

C

Gravity and air resistance