1. The Law of Conservation Of Energy

2. Law of Conservation of Energy: Energy cannot be created or destroyed, only changed from one form into another.

3. As the ball travels upwards Ek is converted into Ep
Imagine a ball being thrown up into the air:
As the ball travels upwards Ek is converted into Ep
As the ball falls downwards Ep is converted into Ek

4. This is similar to a pendulum:

5. On roller coasters the largest hill is always the first. Why is that?

6. When only conservative forces (like gravity) work on an object, Ek is converted into Ep and vice versa.
When external forces like friction are at work then energy is not conserved.
Friction converts some energy into heat

7. The Law of Conservation of Energy:
ΔEk = - ΔEp
Since no energy is lost, the total initial energy must equal the total final energy:
Eki + Epi = Ekf + Epf
½mvi2 + mghi = ½mvf2 + mghf

8. Ex: While jumping over The Great Wall of China an 82 kg skateboarder needs to leave the ramp traveling at 78 km/h. a) How much potential energy does he need to start with? b) What minimum height of ramp should he use?

9. A 65 kg snowboarder starts at rest, travels down a hill into a gulley and back up the other side as shown. Find his speed at the top of the 2nd hill.
45 m
25 m

10. Collisions Elastic: Inelastic:
Kinetic energy is conserved
Nearly occurs with hard elastic objects such as steel, glass and hard plastic
Inelastic:
Kinetic energy is lost and is converted into thermal energy
Soft, sticky materials such as clay behave this way
Don’t forget, momentum is conserved in both cases