Make your own crater
Why don't you try to do your own crater! Be it at home or in school, it does not take a lot to experiment some funny physics. Take a big pan and fill it half up with flour. Then take a sieve. Put some cacao powder in it and let some of this powder fall on to the flour pan until it ends up making a fine dark layer. You can then throw a pebble (watch for your clothes and be sure you are in a safe area) into the pan, producing a crater. The one shown here was produced by students from the Sonderborg Observatory, Denmark. It bears strong ressemblance with the Copernicus Crater on the Moon as observed by the same students.
For more ideas on crater physics, you can also see one of the winning projects of this year Catch a Star! contest.
For more comet science exercises, look at the Astronomy On-Line project on Comet Hale-Bopp.