Wondering about Falling Objects on the Moon

First, Emily gave each of the groups two equal-sized balls– one heavy and made of metal, and one light, hallow, and made of plastic. She asked them to think about what would happen if she dropped both of the balls at the same time. Most students reported thinking that the heavy ball would hit the ground first, because gravity would pull on it more. They were surprised to observe both of the balls hitting the ground at the same time! They also pushed a lead brick and a Syrofoam brick (both covered in duck tape so they looked the same). We discussed that the Earth pulls heavy objects harder than light objects but heavy objects are also harder to get moving, so things work out so that heavy and light objects fall at the same rate. Then we watched astronauts dropping balls on the moon (http://www.youtube.com/watch?v=5C5_dOEyAfk). We ended class by watching a video of first grade students talking about a book and a piece of paper falling (first a flat piece of paper and then the crumpled paper).