5 Lies Tennis Players Think Are True
Have you ever been told to “swing harder” or “follow through over your shoulder”? There’s a good chance the advice may not be grounded in science. Here are 5 lies most tennis players think are true:
1. Swinging fast makes the ball go fast
To hit fast, you need to swing fast. It sounds right, but it isn’t true. Think about what happens when you return a fast serve. Have you noticed that even if you just stick your racket out and block the ball, it jumps off your stings with a lot of speed. You didn’t swing fast, you barely swung at all.
On the other hand, have you seen intermediate players swing as fast as they can, but struggle to get any pace on the ball? Have you watched pros practice? Have you noticed that they seem to generate effortlessly power without swinging fast?
The reason for this apparent contradiction is the difference between acceleration and velocity. Velocity is the speed at a given point, while acceleration is the rate of change in speed over time.
The speed of the ball is proportional to the acceleration (force) on the ball, not the velocity at the point of contact. You can swing fast and have high velocity, but low acceleration because you were swinging at mostly the same speed throughout the stroke. You can have low velocity, but high acceleration if you quickly increase your speed from zero to a non-zero velocity. The pros may be swinging slowly as they warm up, but their arms are loose and they use the power from their core to snap their rackets through the ball like whips, generating incredibly high force and acceleration on the ball.
2. Slice makes the ball go low
Have you ever heard a coach tell you “Slice keeps the ball low”? It’s not true. It’s actually the opposite. Slice causes the ball to rise. Slice is backspin. When the ball spins backwards, it pulls air underneath it, pushing it upwards, causing the ball to rise. This phenomenon is called the Magnus effect.
The reason slice usually goes lower than topspin has to do with the trajectory of the swing, not the spin. When a player hits slice, they often hit down on the ball, going from high to low. The fact that slice causes the ball to rise allows them to hit down and still have the ball clear the net.
3. Topspin makes the ball go high
You’ve probably seen players with heavy topspin hit balls that bounce over your shoulders. If someone told you their balls bounce higher because of topspin, they would be incorrect. It makes their balls bounce lower than if they have the same racquet trajectory but used slice. Topspin means the ball is spinning in the forward direction. The forward direction of the spin pulls air above the ball, pushing it downward.
You might be wondering why players who hit high bouncing balls hit with heavy topspin. The reason is topspin pushes the ball down faster. This allows them to hit very high over the net without the ball going long. The ball is hit so much higher over the net than a slice, the bounce feels higher, even though the bounce is relatively less high than it would have been for a slice shot with the same racket trajectory.
4. Hitting “flat” is possible
Hitting a ball with zero spin is close to impossible. If you don’t believe it, try it for yourself. Pick up a ball and try to toss it in the air without it spinning. It’s hard.
Spin is the angular velocity on the ball. Spin is measured in rotations per minute (rpm). If you see a ball rotate in the air, even a little bit, it has spin. A pro hitting “flat” still has much higher rpm than the average recreational tennis player hitting topspin.
5. Focus on the point of contact
A tennis ball contacts the racket for 1/250th of a second. This is the brief period of time when the acceleration, angle of the racket and other variables determine the trajectory of the ball. In that short amount of time, you cannot make last minute adjustments to your swing path, “feel the ball”, “come around the ball”, or any other adjustments that assume you have plenty of time when the ball hits your strings. The trajectory of the ball has been decided before it makes contact with your racket.
Because the time is so short, this also means that when you watch a professional tennis player to learn, most of what you can observe of their technique misses the most crucial part: the contact point. We can’t see what happens in the 4 milliseconds when the ball contacts the racket. Even if you are watching a tennis video online at 60 frames per second, you can’t catch the point of contact. Most tennis technique happens in the mind’s eye and is not observable. This is why some professionals say they try not to think too about their strokes too much while hitting, instead deferring to their subconcious muscle memory, which is far faster at processing.
Why is this important?
Most tips are reductions of complex concepts like the physics of tennis. These simplifications are necessary otherwise the beginner might get turned off from the game forever if their coach started with a physics lesson.
However, at some point the inaccuracy inherent in oversimplification may hurt a player trying to get to the next level. They might focus on details that don’t matter. If you would like to have a deeper understanding of the game of tennis, then you might enjoy learning more about the physics behind it.
Sources
Want to learn more? Here is a paper that explains one of the most important physics concepts in tennis: