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Ahh, tennis. The sport of kings.
Wait, that’s horseracing. Tennis is the sport of rackets. Well, a sport of racquets. Lots of sports have racquets, and the scientific principles we’ll discuss today apply to pretty much all of them. But tennis is probably the most high-profile and popular racquet-based sport (there really isn’t a Wimbledon equivalent for, like, pickleball), so we will focus on it.
Tennis is one of those sports that, like soccer, doesn’t require a ton of equipment. You need a court, a net, a ball, and a racquet. And you can probably get away without the net if you’re just playing around. There’s a lot of physics that goes into the way the ball and racquet interact, and today we’re going to focus on the racquet side of it. Why? Because we can build some makeshift racquets to experiment with. Balls are a bit harder to manufacture on demand.
While testing racquets today, we’ll be making sort of extreme versions of how racquets work to really demonstrate the point: the tension in the strings makes a lot of difference in how the racquet interacts with the ball.
Materials:
- Corrugated cardboard (just save an old Amazon box)
- Scissors
- Long rubber bands
- Tape
- Tennis balls
- A lab assistant
Process:
- Cut out two ovals of cardboard to be your mini racquets. Make them about 8 inches wide and about 12 inches long, and try to make sure they’re as equal in size and shape as possible.
- Cut out a smaller oval from the middle of each racquet to leave space for the strings. The resulting oval outline should be at least 1 inch thick all the way around.
- Use your scissors to cut a bunch of rubber bands so that they’re one single string instead of a loop.
- Now we are going to string your racquets. We will string the first one with high tension. Stretch a rubber band nice and tight across your first racquet hoop and tape both ends down to the hoop. Repeat this, with rubber bands running parallel until you have a nice series of lines. Now repeat the process with rubber bands running perpendicular (at a 90-degree angle) to your first set, just like a tennis racquet. If you want to get fancy, you can weave these through your first set, but you don’t have to. Once you’re done, cut off any excess rubber band around the outside.
- Your second racquet is going to be strung with low tension. This time leave a little bit of slack in the rubber bands as you tape them down, but otherwise, repeat the same process as step 4.
- Now let’s test. Here’s where your lab assistant and your tennis balls come in. Start with your high tension racquet. Hold it out flat and have your assistant drop a tennis ball onto its center. What happens to the ball? Repeat this a few times until you’ve established a good pattern of how the ball tends to bounce.
- Now do the same with your low tension racquet. Was there any difference? If so, what was different?
- If you have extra time and supplies, try making a super low tension racquet. Tie rubber bands together to make each one double-length before stringing your racquet. When you’re done, it might look something like a butterfly net. What happens when you drop a ball onto this one?
Summary
As you undoubtedly noticed, the amount of tension in the racquet affects how the ball bounces back off of it. Different things will have happened depending on the difference between your high and low tension racquets.
In tennis, each player determines what level of tension they like their strings to have. Racquets all have a minimum and maximum tension, and players choose their level from that range. There are two big differences in how the ball reacts to the racquet based on the tension: speed and control.
A low tension racquet can really get the ball moving thanks to something called the “trampoline effect.” When the ball hits the strings, it pushes them out, like a person jumping on a trampoline pushes the trampoline down wherever they hit. A low tension racquet stretches more since the strings aren’t as tight, which means that they also bounce back more when they release the energy they’ve absorbed, propelling the ball further. The downside is that a bouncier racquet/ball combo means it’s harder to precisely control where the ball goes.
A high tension racquet is the opposite. It has less of a trampoline effect since the strings are tighter, so balls won’t go as fast coming off of it. But this allows a tennis player to have better control over where the ball goes when they hit it.
Depending on the difference between your two racquets, you might have seen this: that the low tension racquet bounced the ball slightly higher than the high tension one. On the other hand, if your low tension racquet was really low tension, the strings would absorb more energy than they could give back, and the ball wouldn’t have bounced as high. If you tried the super low tension racquet option at the end, you would have seen the ball just fall into the strings and hang out there. Cause a super low tension racquet is basically just a net. And I guess a super high tension net is basically just a racquet. See, we all learn something with these experiments!
Just don’t go catching butterflies with a tennis racquet. It probably wouldn’t be good for the butterflies.
Want more Saturday Science? See all of our at-home activities on the blog or on Pinterest. Also, be sure to put the science of sports to the test at the Riley Children's Health Sports Legends Experience. You can raise your racquet for the love of the game at the Seymour and Rheta Holt Tennis Center!
