Science Buddies: "Ask an Expert"

The science project is to find out the physics of follow through when swinging a bat.

The plan is to have the same batter hit 20 new softballs off a tee and measuring the distance the ball travels. After a 10 minute rest, the same batter would hit the same 20 balls off a tee but only making contact with the ball (not follow through). The distance the ball traveled would again be measured. We will use a bat speed radar gun to monitor the speed of each swing so that we can use the formula of force = mass x acceleration. The project will prove that the force behind the swing using follow through allows the ball to travel farther. Does this sound like we are on the correct path?

That's a great start. In addition, you might see if you know anyone that has a digital camera that can shoot in some sort of slow motion. Record the swing. If you look at it frame by frame, can you see something about how the bat accelerates and decelerates that might help explain any difference in how the ball travels?

We had planned to use the digital camera so that pictures could be used for the display. Do you think the acceleration and deceleration should be discussed in regards to the "force" that is placed on the ball (decelerating the bat speed to only make contact or accelerating the bat speed for follow through)?

Hi lbarnes777,

It certainly sounds like you are on the correct path, as you've set up an experiment with an independent variable that you can control and a dependent variable that you can measure. One word of warning - you should be careful about applying F=ma in this case. The bat only exerts a force on the ball when it is in contact with the ball. So, measuring the speed of the bat during the swing (but before it hits the ball) doesn't tell you anything about the force on the ball. Like Howard suggested, if you can get a camera that can film in slow-motion (many modern smartphones have a "slow motion" option built-in to their camera), then you can look at the video frame-by-frame and determine how the ball accelerates (and use that to calculate the force on the ball). If you include a scale in your video (for example, a ruler), then you will know the exact distances in your video and can calculate the proper units (for example, acceleration in meters per second squared). Note that to do that, you will also need to know the framerate of the camera so you know how much time passes between each frame (for example, if the camera is shooting at 120 frames per second, then one frame is 1/120 = 0.0083 seconds).

We have a project that explains how to use a program called "Tracker" to analyze videos like this. This project happens to be about throwing a football but you could use the same basic procedure for hitting a baseball. It might be helpful for your project:

https://www.sciencebuddies.org/science- ... #procedure

http://www.cabrillo.edu/~dbrown/tracker/

Good luck!

-Ben