How far does ejecta fly?
The question
How does the energy of an impact affect how far the ejecta is thrown?
Young craters on the Moon, such as Tycho, have bright rays of ejecta that stretch hundreds of kilometres. In a model, the length of the rays shows how energetic the impact was.
Equipment
- A large tray of flour with a dark top layer of cocoa or powder paint
- A ball and a metre rule
- A large sheet of dark paper around the tray to catch far-flung ejecta
- A ruler, camera and eye protection
Method
- Drop the ball from heights of 25, 50, 75 and 100 cm.
- After each drop, photograph the crater from above and measure the length of the three longest rays from the centre of the crater.
- Level and re-dust the surface after each drop, and repeat each height three times.
- Calculate the energy of each drop using mass × 9.8 × height (in kilograms and metres).
- What to measure
- Crater diameter and mean ray length for each height, and the energy in joules.
- How to present it
- Photos, a results table and a graph of ray length against energy. Compare the ray length to the crater width: is the ratio the same each time?
- Take it further
- Find out why rays fade over time on the Moon, and what they tell scientists about the age of a crater.
Safety
Eye protection on; drop, never throw; sweep up spills at once.