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Players definitely use backspin to increase their chances of having their shot hit “nothing but hoop” (going straight in without touching the rim). The wrist flip creates a difference in pressure and generates an upward force that counteracts the downward force of gravity. The result is that the flick of the wrist adds lift to the shot, and added lift means more range and an improved angle of entry to the hoop. Furthermore, when an object like a basketball spins and then bounces off another object like a backboard, the ball tends to bounce in the same direction of the spin. This means that that bounce will much more likely send the ball downward into the hoop. When players don’t put backspin on the ball, the ball usually bounces away from the hoop. What are the principles of physics behind backspin? The law of physics that governs backspin is called conservation of angular momentum . This law states that an object (the basketball) will keep spinning at the same rate after it leaves the fingertips of the shooter. A ball that isn’t spinning has one motion—the center of the ball moving through the air. Therefore, when the ball hits the rim, the collision slows down the basketball by taking away some of its energy. A spinning ball is the sum of two different motions. Not only is the center of the basketball moving through the air, but there is also motion caused by the ball spinning around its own center. When you add those motions (forces) together, the bottom of the ball moves faster than it would with no spin. In this shot, the collision of the bottom of the ball with the rim occurs with a greater speed because the ball has more friction, so there is more loss of energy, thus slowing the ball down. Is a slower ball a good thing? Yes, it is, because it is more likely to go into the hoop if it has less energy.

12 CONNECTING STEM AND SPORTS | BASKETBALL