9781422274774

Have you ever wondered what’s happening when a skydiver appears to

be hovering in the air? The hover means the net force is zero. About twelve seconds after the jump, the skydiver reaches a speed where the air resistance force increases to balance the force of gravity. The air is pushing up on the skydiver with the

Air pushes on a skydiver falling toward the earth, but the skydiver is pushing on the air as well.

exact force that gravity is pulling them down. When net forces are zero, momentum is constant, and therefore momentum also equals zero. It looks like magic, but it is really physics! Once a skydiver learns how to hover, they can move on to more complex moves. Moving Up or Down Of course, any skydiver wants to do more than just hover in the air. How do they do the cool stuff? Think of a skydiver’s body as a board. If a human is stretched straight out as tall (or as long) as possible, then the air resistance is hitting a larger object, or a larger surface area . What do you think happens if the skydiver tucks his or her body into a tight ball, kind of like doing a cannonball in the pool? In figure 1, the left image depicts a skydiver with zero net force.

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