For an extra challenge, attach a paper cone to the balloon nose. Again, ask the children for their predications before observing the results. With the balloon closed, the air inside is under pressure and tries to expand in every direction. A large force is exerted by the air, but since this pressure is equal in all directions, no movement occurs. When the balloon opening is released, the air movement is all in one direction, forcing the balloon to move in the opposite direction.
Drop marbles on the smooth surface.
Drop marbles on the sandpaper, making sure you drop them from the same height as in step one. Have the children observe what happens to the marbles as they land on the smooth surface. Ask them to predict what will happen when they land on the sandpaper. Set up your surfaces in the classroom. Have the children predict how the coin will move on each surface.