Set out the materials as a centre or have children work in pairs (one strong reader with a weaker reader) and have children follow the procedures to make their own cars. When enough cars are made, they can be used for further experiments in other centers. Use them to test gravity down different sloped ramps. Measure the distances they travel. Test friction and momentum as the cars travel along various surfaces like cardboard, linoleum and carpet. Test to see what kind of a load each car can carry as a strong and stable structure.