1. Potential and Kinetic Energy

2. What is Energy Energy is the ability to do work.
Measured in Joules (J).
Mechanical energy is the energy due to the position of something or the movement of something.
Energy is never created or destroyed, it is only transformed into a different form.

3. Forms of Energy Chemical - gasoline Electrical - lightning
Heat – burner on a stove
Light – flash light
Mechanical - car
Nuclear - sun
Sound – music on the radio

4. Potential and Kinetic Energy
Mechanical Energy
What are the two forms of mechanical energy?
Potential and Kinetic Energy
Energy that is stored is called potential energy (PE) because in the stored state it has the potential for doing work.
Three examples of potential energy are elastic potential energy, chemical energy, and gravitational potential energy.

5. Examples of Potential Energy:
A stretched rubber band..
Water at the top of a waterfall..
Yo–Yo held in your hand..
A drawn Bow and Arrow…

6. Potential Energy
Work is required to elevate objects against Earth’s gravity.
The potential energy due to elevated positions is gravitational potential energy (GPE).
The higher an object, the more potential energy.
The more mass an object has, the more potential energy it has.

7. Potential Energy
The amount of gravitational potential energy possessed by an elevated object is equal to the work done against gravity to lift it.
GPE = mgh
The height is the distance above some chosen reference level, such as the ground or the floor.

8. Potential Energy
The potential energy of the 100-N boulder with respect to the ground below is 200 J in each case.
The boulder is lifted with 100 N of force.
The boulder is pushed up the 4-m incline with 50 N of force.
The boulder is lifted with 100 N of force up each 0.5-m stair.

9. Kinetic Energy
When stored energy begins to move, the object now transfers from potential energy into kinetic energy.

10. Kinetic Energy
If an object is moving, it has energy. (Be careful, the converse of this statement is not always true!)
This energy is called kinetic energy - the energy of motion.

11. Kinetic Energy An object’s kinetic energy depends on:
the object’s mass.
Kinetic energy is directly proportional to mass.
the object’s speed (velocity).
Kinetic energy is directly proportional to the square of the object’s speed.

12. Potential Energy Check
If I want to drop an apple from the top of one of these three things, where will be the most potential energy? A C B
Since the tower is the highest off
the ground, the apple would have
the most PE (PE = mgh)

13. Kinetic Energy Check
When these objects move at the same speed, which will have more kinetic energy?
The truck will have a higher KE at the same
speed because it has a larger mass
KE = ½ mv2

14. Work – Energy Theorem
When you throw a ball, you do work on it to give it speed as it leaves your hand. The moving ball can then hit something and push it, doing work on what it hits.
Common units of kinetic energy: Joules

15. Work – Energy Theorem
The work-energy theorem describes the relationship between work and energy.
Work = ∆KE; ΔPE = -Work
Work equals the change in kinetic energy.
The work in this equation is the net work—that is, the work based on the net force.