Unit 4: Potential EnergyPotential Energy is the energy

associated with an object because of the position, shape, or condition of the object.

Unit 4: Potential EnergyPotential energy is stored energy.

Gravitational potential energy is the potential energy stored in the gravitational fields of interacting bodies.

Unit 4: Potential EnergyThe SI unit for potential energy is

the joule (J).

Unit 4: Potential EnergySuppose 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.

Unit 4: Potential EnergyGravitational 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.

Unit 4: Potential EnergyElastic 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

Unit 4: Potential EnergyExample: 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. (PEtotal = 3.43x104 J)

Unit 4: Potential EnergyIn summary: energy is the

potential to do work.

Unit 4: Potential EnergyHomework

◦Worksheet – Potential Energy◦Vocabulary:

Potential Energy Gravitational Potential Energy Elastic Potential Energy Spring constant