Does a slanting impact make an oval crater?
The question
How does the angle a ball hits the sand at change the shape of the crater and where the ejecta lands?
Most space rocks hit the ground at a slant, yet almost all real craters are round, because a high-speed impact releases its energy like an explosion. Only very shallow impacts, below about 10 to 15 degrees, make oval craters.
Equipment
- A deep tray of flour or sand with coloured powder on top
- A cardboard tube, such as from kitchen foil, and a marble
- A protractor
- Modelling clay or books to hold the tube at an angle
- A ruler and eye protection
Method
- Prop the tube so its lower end is just above the surface, at 90 degrees (straight down).
- Roll the marble down the tube and let it hit the sand. Measure the crater's length and width.
- Repeat at 60, 45, 30 and 15 degrees, measured from the surface, keeping the top of the tube at the same height.
- Photograph each crater from directly above with a ruler beside it.
- What to measure
- The length and width of each crater, and the length divided by the width (1 means round). Note which side the ejecta lands on.
- How to present it
- A row of photos from 90 to 15 degrees, a table of length, width and their ratio, and a conclusion comparing your slow craters with real high-speed ones.
- Take it further
- Find out why the low speed of your marble matters: in slow laboratory impacts, craters become oval at steeper angles than they do in real high-speed impacts.
Safety
Eye protection on, and keep faces back from the tray.