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Friction We’ve already talked about two forces that act on the ball— gravity and lift. Gravity pulls the ball down toward the ground as it is in flight. Friction creates the drag force on the ball. Friction occurs as two surfaces (the ball and the air) make contact with each other. As the basketball comes into contact with the air, drag forces act opposite to the ball’s motion and slow it down. Drag is the force of the air pushing on the ball as it travels in flight. Think of drag as air friction. The air around the ball helps slow it down. Remember Newton’s Second Law, the law of inertia, which states that an object in motion continues in motion with the same speed and in the same direction unless acted on by an unbalanced force. Magnus Force In addition to gravity, lift, and friction, a fourth, more subtle, force also acts on the basketball. It’s called the Magnus force, and it happens when the ball is spinning. The force is named for German physicist Gustav Magnus, who first described the spinning effect in 1852. Magnus witnessed cannonballs and bullets flying through the air and wondered why these objects deflected (curved) toward one side or the other rather than traveling in a straight path.

CHAPTER 1 : FORCES THAT ACT ON A BASKETBALL

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