How Do Newton's Laws Of Motion Interact With Tennis?

Physics plays an important role in tennis, as wind, gravity, the racket and the ground all affect the balls you hit. Sir Isaac Newton's three laws of motion come into play in different ways than in other sports, such as golf, where the ball remains motionless until you strike it, or bowling, where the pins remain motionless until your ball strikes them. In tennis, the point starts with you tossing the ball, so the ball is always in motion when you make contact with it.

Newton's Laws of Motion

Newton's three laws of motion state roughly the following: An object at rest stays at rest, and an object in motion will remain in the same motion unless an external force is applied to it; force is equal to mass multiplied by acceleration; and for every action there is an equal and opposite reaction.

Newton's First Law

If a tennis ball is traveling toward you at 60 mph when it comes off your opponent's racket, it will be traveling at 60 mph when it reaches you unless some other force affects it. The forces that slow a tennis ball as it comes to you include gravity, which lowers the ball as it travels, and the air, which causes the ball to slow. When the ball hits the ground, it experiences friction, which further slows it after the bounce. By the time the ball reaches you, it is traveling slower than when your opponent hit it. The final aspect of Newton's first law regarding an incoming tennis ball is that your racket is an external force acting on the ball, sending it into the opposite direction when you hit it.

Newton's Second Law

In the equation force = mass x acceleration, mass is the ball and the racket; there's not much you can do about the ball, but buying a heavier racket adds mass to your shot, while a lighter racket might let you create more acceleration. For most players, if you want to hit the ball harder, you want to accelerate your racket more. Gripping the handle of the racket tightly in an effort to hit the ball harder can cause tension in your muscles, slowing your arm swing. Relaxing lets you swing the racket faster, create more acceleration and hit the ball with more force. A famous golf book paraphrases this with its title, "Swing Easy, Hit Hard."

Newton's Third Law

Newton's third law states that when an action occurs, such as a tennis racket striking a ball, there is an opposite and equal reaction. This law comes into play when you strike the ball with the racket, sending the ball in the opposite direction. Additionally, when you push off the ground during a groundstroke or serve, this accelerates your body away from the ground, helping you create more racket head speed. The new style of strokes, with extreme coiling and uncoiling of the body causing players to jump off the ground because of their push off, is a recent application of Newton's third law to tennis, according to Louis Cap, a Ph.D. in physics and international certification tester for the Professional Tennis Registry.