1. Unit 4: Potential Energy Potential Energy is the energy associated with an object because of the position, shape, or condition of the object.

2. Unit 4: Potential Energy Potential energy is stored energy. Gravitational potential energy is the potential energy stored in the gravitational fields of interacting bodies.

3. Unit 4: Potential Energy The SI unit for potential energy is the joule (J).

4. Unit 4: Potential Energy Suppose you drop a volleyball from a second-floor roof and it lands on the first-floor roof of an adjacent building. ◦ If the height is measured from the ground, the gravitational potential energy is not zero because the ball is still above the ground. ◦ If the height is measured from the first-floor roof, the potential energy is zero when it lands on the roof.

5. Unit 4: Potential Energy Gravitational potential energy is measured from some zero level and that level is arbitrary. In many cases the statement of the problem suggests what to use as a zero level.

6. Unit 4: Potential Energy Elastic potential energy: the energy available for use when a deformed elastic object returns to its original configuration ◦ k, spring constant: a parameter that is a measure of a spring’s resistance to being compressed or stretched

7. Unit 4: Potential Energy Example: A 70.0 kg stuntman is attached to a bungee cord with an unstretched length of 15.0 m. He jumps off a bridge spanning a river from a height of 50.0 m. When he finally stops, the cord has a stretched length of 44.0 m. Assuming the spring constant of the bungee cord is 71.8 N/m, what is the total potential energy relative to the water when the man stops falling? Hint: this includes gravitational and elastic PE. (PE total = 3.43x10 4 J)

8. Unit 4: Potential Energy In summary: energy is the potential to do work.

9. Unit 4: Potential Energy Homework ◦ Worksheet – Potential Energy ◦ Vocabulary:  Potential Energy  Gravitational Potential Energy  Elastic Potential Energy  Spring constant