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You probably remember hearing about Newton’s Second Law of Motion in the form of force equals mass times acceleration. Today, you need to brush up on your physics to understand why force is important for you as a tennis player. Like most tennis players, you probably run to get in position and then swing without using your bodyweight. If you’re just swinging and using a bit of rotation from your shoulder turn, what kind of force are you generating and what is the direction of that force? Is your swing all the force you can exert on the ball or can you maximize using all your bodyweight?
First, let’s go over two key points of Newton’s Second Law of Motion (quoted from a Vanderbilt University course material):
Newton's Second Law, F = ma is a vector equation. It says that the net force (a vector) acting on a mass m (a number) causes an acceleration (a vector) of the object in the same direction as the net force.
The net force is the combined force of all individual forces acting on an object.
Force is something that you exert on the tennis ball. Force and acceleration are vectors, which means that there is direction involved in force. Intuitively you know this — whatever you accelerate won’t remain in a stationary position, otherwise you wouldn’t be accelerating the object. So, the acceleration also gives you direction. Furthermore, you’re accelerating mass. So force is basically mass accelerating in a direction (i.e., F = ma, duh!!).
The second bullet tells you that you’re accelerating mass onto an object (the tennis ball) and that it can be a combination of several masses accelerating together onto the tennis ball. For tennis, the combination of masses would be your racquet, plus arm, and the rest of your body. Unfortunately, the default thinking is to swing and only use the weight of your arm and racquet with a fraction of your bodyweight. That needs to change if you want your game to reach a better level. You must use all of your bodyweight whenever you have the space and time to do so.
Here are three other benefits to adding bodyweight to your shot:
(1) Bodyweight frees your arm to swing faster. When you don’t use bodyweight, your instinct is to tense your arm so you can feel like you’re adding power. However, tension slows down your swing. Instead, you end up strangling your grip. Bodyweight gives you support to relax and swing fast.
(2) The force is with you. You might not be a Jedi, but when you add all your mass you can generate more force and make your opponent feel a “heavier” ball. That’s because your force translates into the ball’s momentum. They will need to work harder to manage your shots because your ball will come with greater momentum. .
(3) By applying all your bodyweight into the tennis ball, you also get more control over the direction the ball travels. Recall that force is a vector. It will travel in a specific direction. When you only swing and don’t commit to using your bodyweight, your body may shift back or sideways. This alters the direction of your swing-path and makes it more difficult to be accurate with where you want the ball to go. But if you entire body is moving in the same direction, then there won’t be any confusion about where the ball will travel.