# Slam Dunk Science

## PHYSICIST EXPLAINS BASIC PRINCIPLES GOVERNING BASKETBALL

November 1, 2007

Basic physics can help players improve their game. Putting backspin on the ball results in a soft touch from the free throw line because the spin reacts with the backboard to bounce the ball into the basket. Players should launch jump shots from the apex of a jump, because the shooter is not moving at that point, which offers the best possible control of the ball.

## Science Insider

BACKGROUND: Good basketball players develop their skills through endless repetition, hard-wiring the brain with the correct sequence of muscle movements for optimal play ('kinesthetic memory'). However, knowing a little basic physics can still help you improve your game. You can learn why you should put a spin on the ball, get tips on improving your free throws, and discover the secret to Michael Jordan's seemingly longer 'hang time.'

PUTTING A SPIN ON IT: Once the basketball leaves the shooter's hand, it travels in an unchanging parabolic path that can be calculated using Newton's laws of motion. But putting a backspin on the ball can help you make more free throws. When a spinning ball bounces, it bounces back in the direction of the spin. If the ball hits the backboard or back of the rim, it will be directed toward into the basket. That's because when the ball makes contact with the rim or backboard, the backspin causes a change in velocity opposite to the spin direction, making it more likely that the ball will drop into the net softly.

BOUNCE, BOUNCE: Hold a ball in the air above the floor and it has potential energy. Dropping the ball converts it into kinetic energy. When the ball hits the floor, the kinetic energy is stored as elastic potential energy, in response to which both the ball and the floor will deform, or dent, slightly, even if this isn't obvious to the naked eye. Air stores and returns energy more efficiently than the material from which the basketball is made. So the more air pressure inside a basketball, the less its surface will bend or deform during a bounce, and the more its original energy will be stored in the compressed air inside -- ergo, the ball bounces higher the more air it has inside it. If the ball is under-inflated, some of its energy is wasted in deforming the ball as it bounces, and the ball won't rebound very high.

HANG TIME: Michael Jordan earned the nickname 'Air Jordan' because of his seemingly longer 'hang time' making jump shots in games, but this is an illusion. How high someone can jump depends on the force used to push on the floor when starting to jump, which in turn depends on the strength and power of the jumper's leg muscles. The harder and more powerful the jump, the higher and longer the flight. In order to leap four feet into the air, the hang time would be 1.0 seconds. Jordan had a few tricks up his sleeve to make that hang time seem longer. When he dunked, he held onto the ball a bit longer than most players, and actually placed it in the basket on the way down. He also pulled his legs up as the jump progressed so it appeared that he was jumping higher. But it still all happened in less than one second.

The American Association of Physics Teachers contributed to the information contained in the TV portion of this report.

## Latest stories

ON THE WEB:
mrfizzix.com
NPR story
Discover story

TO GO INSIDE THIS SCIENCE: