This concept will resurface in the Post-Visit Exploration. It usually takes between three and five strokes to move the ball to the top of the tower. Working in pairs, one child at each handle, even small children can move the ball to the top. Air forced by the pump pushes the ball up the plastic tube, and gravity makes it come down. Encourage students to use their powers of observation to try to figure out why the ball doesn't bounce straight up and down.
Gravity pulls the dropped ball straight down to the floor.
When the ball is placed on the blower, it floats because air is holding it up, pushing against the downward pull of gravity. Remind students that gravity is still pulling down on the ball, but that the air is pushing just as hard, so that the ball remains suspended. A little experimentation shows that because our roof is not fastened down, air gusting under the edge of the roof will blow it off. The air moving over the top of the roof exerts less pressure than the air inside the house. When the balloon is at rest it sits on a platform, held down by the pull of gravity.