Does drop height change the size of a crater?
The question
How does the height a ball is dropped from affect the width of the crater it makes?
A ball dropped from higher up is moving faster when it lands, so it carries more energy. Real space rocks hit at enormous speeds, which is why their craters are so large.
Equipment
- A deep tray of flour or fine sand with cocoa or coloured sand on top
- One ball, such as a marble or golf ball
- A metre rule and a 30 cm ruler
- A flat piece of card for levelling
- Eye protection
Method
- Level the surface and dust it with cocoa.
- Drop the ball from 20 cm, measured from the surface to the bottom of the ball.
- Lift the ball out carefully, measure the crater across in two directions and take the average.
- Level the surface again and repeat three times at each height: 20, 40, 60, 80 and 100 cm.
- Keep the ball, the tray and the levelling the same every time.
- What to measure
- Crater width in centimetres (the average of your repeats), and the length of the longest ejecta streak.
- How to present it
- A results table and a line graph of crater width against drop height, with a sentence describing the pattern. Does doubling the height double the width?
- Take it further
- Use balls of the same size but different weights, such as a ping-pong ball and a golf ball. Which affects the crater more, weight or height?
Safety
Eye protection on. Drop, never throw. An adult holds the metre rule for the highest drops; nobody stands on chairs.