Science Buddies: "Ask an Expert"

Ok. I have a physics project. I have to find how the velocity of a bat affects the distance of a ball on a batting tee. The problem I am having is creating a device to have the bat moving horizontally while being able to test the velocity of the bat. If you have any ideas on how i can create this device, please write back! Anything will help! Thanks!

Hi WMedina13,

for an idea how to build the batting device, take a look at the following project:

http://www.selah.k12.wa.us/SOAR/SciProj ... .html#exde

Now, to measure the bat's velocity, remember that velocity can be measured as distance over time. In principle you could start and stop a stopwatch at two points along the bat's swing path, perhaps by electronic contact (put switches in the bat's way) or opto-electronically (bat crosses beam of light). A stopwatch circuit is a simple electronic circuit that is often used for instruction in electronics classes - you may be able to find a simple kit at an electronics/hobby store or online, or if your school offers electronics classes somebody there may be able to help you.
Keep in mind, though, which velocity it is that you really want to measure. For example, if you use a springload to move the bat, the velocity will most likely not be constant over the full swing path. What you're interested
in is the velocity at the moment of impact. Also remember that if the bat swings in a circular motion, you're really measuring angular velocity so it is important to measure it at that point along the bat's length which is actually going to hit the ball. If that's not technically possible, you can correct your result for the desired radius.

I hope this helps to get you started. Let us know how your project progresses!
Cheers, Ivo

I can think of a fairly simple method to measure the velocity of the bat - if you have a video camera.

1 Mount the camera above the bat, pointed exactly straight down.
2 Mount a measurement device directly under the camera, and below the plane the bat will swing through. This can be a sheet of poster board with lines on it at a known distance. This is so you can measure how far the bat moves
3 Start recording
4 Swing the bat, using whatever method you choose
5 Stop the recording
6 Play the recording back, one frame at a time
7 Using the measurement device under the bat, record how far the bat moved in each frame
8 Look up your camera's "frame rate", that's "FPS", in your user's manual. That will tell you how many frames your camera shoots per second. If you divide 1 by that number, you'll know how many hundreths of a second are between each frame. Typical frame rates are 24 FPS, or "24p", or one frame every 0.042 seconds.
9 Now you know how far you bat traveled in how much time, and you can calculate velocity

Good luck, and have fun.