When a football player throws a tight spiral pass, the ball glides through the air in a smooth arc, its nose pointing up toward the sky at the beginning of the toss, and then dropping down toward the earth as it lands in the receiver’s hands.
The spiral pass is so familiar it’s easily overlooked as just being common sense — but it took physicists nearly 20 years to understand this trajectory.
Conservation of angular momentum suggests that the ball should not act this way. It should either keep its nose angled toward the sky the whole time, or the ball should be flipping over itself as it moves through the air, but the fact that it just tips over elegantly is — to use a scientific term — weird as hell.
But it turns out the solution is easy enough to understand — as long as you have a spinning top.
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