Height and the crater
The formula says potential energy rises with height. This activity shows it happening, using the depth of a crater as the measuring instrument.
Figure to be added
Method
- Spread an even layer of clay on the ground, about 3 cm thick.
- Release a fairly heavy object, such as a steel ball, from a height of 0.5 m above the clay surface.
- Observe the depth of the crater formed where the object landed.
- Now release the same object from several different heights, letting the same face of it strike the clay each time.
- Observe the depth of the crater in every case.
Observation
The greater the height the object falls from, the deeper the crater it makes.
Reading the crater
Making a hole in clay takes energy, and that energy came from the falling object. A deeper hole therefore means the object arrived carrying more energy — so the crater is an indirect way of measuring the energy the object had before it was released.
Higher means a bigger store
The higher an object is placed, the more potential energy it holds. That is the h in m g h, demonstrated with a lump of clay.
Why the same face has to strike the clay
A ball landing on a point sinks further than one landing on a flat side, whatever energy it carries. Keeping the striking face the same is what makes the comparison a test of height alone.