OpenStax College Physics for AP® Courses, Chapter 4, Problem 26 (Test Prep for AP® Courses)

This is College Physics Answers with Shaun Dychko. We're going to examine the forces on a basketball player, and on a basketball as the player is jumping to shoot the ball. Let's look at the player first. The player experiences gravity downwards. I've labeled that F g, and P for player. They're also going to experience a normal force upwards because the player will exert a force on the floor, and then the reaction force from the floor is the normal force upwards. This force and gravity by the way are not Newton's third law action-reaction pairs. The Newton's third law counterpart to this normal force is the force that's on the floor due to the player. The normal force is the force on the player due to the floor. There's normal force upwards is much larger than gravity downwards, and that's why the player will accelerate upwards. There's also a second force downwards and that is the force on the player do to the ball because the player is going to exert a force upwards on the ball. I've labeled that F b for ball due to the P for player. So this is the force upwards on the ball due to the player. This one and this one are Newton's third law pairs. This being the force on the player due to the ball of equal magnitude, but in the opposite direction to this force. If the player was not trying to accelerate this ball, then they would otherwise accelerate up upwards faster because it'd be a larger net force upwards. But this reaction force due to the force on the ball, which is pushing the player downwards, is going to reduce the net force upwards. There are three important forces on this player, the normal force due to the floor upwards, the force downwards due to gravity and the force downwards due to the ball. Now considering just the ball, we have two forces to look at, one being the gravity downwards and the other being the force due to the player, and this ball is going to accelerate upwards as well.