Stored energy
Potential energy.
A slingshot
Pull back the rubber of a slingshot and hold it. Nothing moves. Let go, and the stone shoots forward.
Where do you think the stone's energy of motion comes from?
What this lesson covers
The idea
Work done to deform an object is stored in it and released by its internal forces as it regains its shape; energy stored due to deformation, or in a system due to relative positions, is potential energy.
A slingshot
Pull back the rubber of a slingshot and hold it. Nothing moves. Let go, and the stone shoots forward.
Where do you think the stone's energy of motion comes from?
- From the stretched rubber
- From the stone itself, with no source
- From the air around it
Stretch and release
Press Next step through the three pictures.
Energy kept in a shape
The coins, the ball and the arrow gained kinetic energy that came from the band, the spring or the bow. Their internal forces undo the deformation and carry out work as they do so. Work done to deform them had been stored.
Work done to deform an object is stored in it and is released by its internal forces as it regains its shape. Energy stored due to deformation, or in a system of objects due to their relative positions, is potential energy.
Notes
Potential energy is energy stored by deformation or by the relative positions of objects; internal forces give it back as the object regains its shape.
Check yourself
A stretched rubber band is released and a stack of coins shoots forward. Where did the kinetic energy of the coins come from?
What is potential energy?
You compress a spring. What happens to the work you do on it?
What makes a stretched band come back to its original shape and push the coins?
- From the coins, which had it already. The coins were at rest and had no kinetic energy. They gained it from the band.
- From the energy stored in the stretched band — correct. Yes!
- From the floor under the coins. The energy came from the stretched band, which had stored the work done to stretch it.
- Energy an object has due to its motion. That is kinetic energy.
- Energy that is lost as sound. Potential energy is stored energy. It is not lost.
- Energy stored due to deformation, or due to the relative positions of objects in a system — correct. Yes!
- It is stored in the spring as energy — correct. Yes!
- It disappears at once. The work done to deform the spring is stored in it. The spring can give it back.
- It makes the spring heavier. Deforming the spring stores energy in it. The spring does not become heavier.
- The force of the person's hand after release. Once the hand lets go, the internal forces in the band undo the deformation.
- The internal forces in the band — correct. Yes!
- The coins pulling the band. The band applies a force on the coins. Its own internal forces undo the deformation.