Hit The Spot! Contributed By: The Franklin Institute

Experiment Category:

Objective:

To experiment with racket angle to determine ball trajectories.

What You Need:
• A wall and a large hard/concrete surface outside (like a garage door and a driveway)
• A tennis racket
• A tennis ball
• A tape measure or meter stick
• 5 sheets of paper
• Magic marker
• A stopwatch (optional)
To Do and Observe:

Make targets out of your paper and magic marker – label them 1 – 5. Tape the targets onto the wall, making sure that they are at least 42 inches (~1.1m) from the ground (a tennis net is 42 inches tall). Tape one high, one just above the “net”, and a couple left and right of center. Take your tennis racket and ball and stand back from the wall, starting at about 8 feet (2.4 m) away from the wall. Bounce the ball on the ground and hit it with the tennis racket. Take a few practice shots then try to hit your targets. What do you have to do to the racket to hit each target? Move back a few paces and try again. Is it easier or harder to hit the targets? How does that change what you do with your racket? Move forward a few paces and try again. Is it easier or harder to hit the targets? How does that change what you do with your racket? Try timing yourself – see how many targets you can hit in 30 seconds. In 15 seconds. If you don’t have a watch, count how many targets in a row you hit without a miss.

What's Going On:

Physics plays a big part in tennis, no matter what your skill level might be. This experiment shows how the angle of your racket affects ball trajectory as you try to hit the targets. Trajectory is the path of the ball once it leaves your racket – the tennis ball makes an arc through the air (much like tossing a baseball will make an arc through the air). The trick is finding the right arc to make the ball land on a target. The vertical angle of the racket is how much you “open” the face of the racket to hit the ball – so a zero degree angle is when your racket face is parallel to the wall, and 90 degrees is when the face of the racket is parallel to the ground. Hitting with a zero degree angle results in a “line drive” or no arc. Increasing the angle will give you a bigger arc in your trajectory, and hit the targets that are higher on the wall.

Parent/Teacher Tips:

An extension of this activity is to discuss how ball speed also plays a role in trajectory. In general, the harder a ball is hit, the further it goes. You can decrease that distance by increasing the vertical angle of your racket (making a bigger arc) while hitting at the same speed.

X