Mass and the crater
The same clay, the same height, and only the mass changed. Changing one thing at a time is what makes the pair of activities prove anything.
Method
- Take a plastic bottle and fill it about one quarter full of sand. Let it fall onto the clay bed from a height of about 1 m, as before.
- Observe the depth of the crater that forms.
- Now fill the bottle about half full of sand and let it fall from the same height of about 1 m as before.
- Finally fill the bottle completely with sand and again let it fall from the same height.
Observation
As the mass of the bottle released increases, the depth of the crater formed increases.
What the two activities prove together
Each activity changed exactly one quantity and held the other fixed, so each one isolates a single factor of the formula.
| Activity | What was changed | What was held fixed |
|---|---|---|
| 18.1 | The height it was dropped from | The falling object, so its mass |
| 18.2 | The mass, by adding sand | The height, about 1 m every time |
Both factors confirmed
Potential energy rises with height and rises with mass. Between them the two activities have demonstrated the m and the h of m g h — leaving only g, which no school experiment gets to change.