What it shows
Craters on the Moon were made by rocks hitting its surface. Dropping marbles into flour from different heights shows that faster impacts make wider craters with longer rays, and that the Moon keeps its craters because it has no air, water or weather to wear them away.
The science
A falling object gains kinetic energy with height, and on impact that energy pushes material outwards and upwards, leaving a bowl-shaped crater and throwing out rays of ejecta. A faster or heavier object delivers more energy, so the crater is wider and the rays longer. The Moon has no atmosphere to burn up small rocks and no rain or wind to erase the marks, so craters from billions of years ago are still there, while on Earth they are mostly worn away.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A deep tray
- Flour about 3 centimetres deep
- A thin layer of cocoa powder or coloured powder on top
- Marbles or stones of different sizes
- A metre rule
- A small ruler to measure craters
Safety
For this project: Drop, do not throw; keep faces away from the tray.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Smooth the flour and sprinkle the dark powder in a thin even layer on top.
Drop a marble from 20 centimetres, measuring with the rule, and lift it out carefully.
Measure the crater width and the length of the longest ray with the small ruler.
Smooth the surface and repeat from 50 centimetres and from 1 metre.
Repeat the whole set with a bigger stone.
Make a table of height, object, crater width and ray length.
Draw a bar chart of width against height.
Compare the look of your craters with a photo of the Moon and point out the rays.
What you should see
Crater width grows with drop height and with marble size, and the dark powder shows bright rays of flour thrown out, just like the rays round the crater Tycho.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What made the Moon's craters?
Rocks from space hitting its surface at high speed.
02Why does a higher drop make a bigger crater?
The marble hits faster with more energy.
03Why does the Earth have few craters?
Its atmosphere burns up small rocks, and rain, wind and plants erase old craters.
04What are the bright streaks round some Moon craters?
Rays of material thrown out by the impact.
Take it further
Drop the same marble at an angle and see whether the crater is still round; real craters usually are.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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