I am late in reading this so someone may have suggested this already, but make meteorite craters.
NASA has a couple guides on this too.
But what you do is take a big pan that is relatively deep and fill it with flour or sand. I like sprinkling a layer of cocoa on the top so that the ejecta blankets look cool. Then you take different mass objects and drop them in from the same height. You measure the depth and width of the crater. Then you pick a mass and drop it from different heights, again measuring the width and depth.
I also then talk about erosion. I pour water over one crater and then blow across the other. In each case the crater changes or disappears.
This is an awesome activity that makes a mess. Kids really like it.
Tina
Tina Fanetti
Physics Instructor
Western Iowa Technical Community College
4647 Stone Ave
Sioux City IA 51102
712-274-8733 ext 1429