Potential Energy

Potential Energy examples Give four examples of an object that has potential energy (not mentioned in the previous power point)

Potential energy – the energy an object or system has by virtue of its position or configuration

Gravitational Potential Energy (U G ) Energy stored due to an object’s position or vertical height

Recall… We defined energy as an object’s ability to do work and…. Work = Force x Displacement In order to gain potential energy due to gravity, somebody/something must put the “work” into the system Knowing this, we can transform the Work equation into one for gravitational potential energy

U G Equation – Work = Force x Displacement The force that must be overcome is due to gravity, therefore, Force = mass x gravity. When changing an object’s vertical position, you cause a displacement…and we’ll just call that h, for height – Now…. Work = (mass x gravity) x height – Once the work has been put into the system, it turns into energy…therefore – U G = mgh

Calculating U G Calculate the U G contained by an Will I. Flye (80 kg), jumping from a height of 1800 meters. Will’s friend, May B. Knot, has a smaller mass (65 kg), but jumps from 1900 meters. Who has more U G ?

Energy Transfer Will and May land…how much U G do they contain now? Knowing energy cannot be created or destroyed, where did the energy go?

Energy Transfer The answer lies in energy’s ability to transform into other forms. Will I. Flye and May B. Knot had U G to begin with, but were not moving. After jumping off the cliff, explain what happens? They start accelerating towards the ground Their height decreases They transferred U G into kinetic energy, K (moving energy)

Other examples of U G transfers into K Write down an example of another transfer similar to this one

Recalling an earlier picture… Why does Katniss have potential energy? Is this U G ? This is called elastic potential energy, U s

Elastic Potential Energy, U s Scalar Measured in Joules, J the energy stored in elastic materials as the result of their stretching or compressing

Meet Mudd…

Elastic Potential Gone Wrong

Calculations using U s U s =1/2kx 2 k = spring constant – Measures how “stiff” the spring is. – Higher the k, the stiffer the spring – Units are N/m x = displacement from equilibrium position Mudd, the jumping bulldog, has a mass of 25 kg, the trampoline has spring constant of 25,000 N/m, and he compresses it 0.1 meters. How much U s does the trampoline contain?

Other examples of energy transfers…