# Ask an Expert: The Science of Spin: A Baseball Pendulum

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### The Science of Spin: A Baseball Pendulum

Hello Scientists,

I have a couple of questions on this science project, The Science of Spin: A Baseball Pendulum Advanced Medium.

For my first question, the grid were supposed to make out of cardboard, what are the dimensions of the grid? Also do we hang the pendulum on something or hold it with our hand?

My next question is, I am interested in this project, I want to incorporate different pitches into this project? How can I make these different pitches relate to this pendulum project of how pitchers throw different pitches and how can I replicate the spins of these pitches; fastball, knuckle, etc?

Thanks

Mark Scheble

I have a couple of questions on this science project, The Science of Spin: A Baseball Pendulum Advanced Medium.

For my first question, the grid were supposed to make out of cardboard, what are the dimensions of the grid? Also do we hang the pendulum on something or hold it with our hand?

My next question is, I am interested in this project, I want to incorporate different pitches into this project? How can I make these different pitches relate to this pendulum project of how pitchers throw different pitches and how can I replicate the spins of these pitches; fastball, knuckle, etc?

Thanks

Mark Scheble

### Re: The Science of Spin: A Baseball Pendulum

Hi Mark,

This particular Project Idea is an "abbreviated" one, which is why the directions are not very complete. So, you'll need to fill in the details yourself; I think that makes a project more fun. But, it can also make things more difficult. Now, let's take a look at those two questions...

It will probably be best to hang the pendulum from something. You want gravity to be the only force acting on the pendulum, and if you hold it in your hand, you might introduce other forces. Be sure to keep the length of the pendulum constant.

The size of the cardboard grid will depend on how high the pendulum swings, because the height of pendulum is related to the horizontal displacement of the ball. You will want to release the pendulum from the same position for every test, and the pendulum will never swing higher the level you release it at. For pendulums, it is sometimes more helpful to release the pendulum at the same angle, as opposed to height, because the angle is easy to measure – just stick a protractor beneath the point where the string connects to whatever the pendulum is hanging from. Once you decide where you will release the pendulum, you can watch the pendulum swing to find out how big the cardboard needs to be. You could also do some simple trigonometry to calculate how big the cardboard piece needs to be for a given angular displacement.

This page from HyperPhysics describes some of the equations that describe pendulums. This particular experiment can be treated like a simple pendulum. Depending on your grade level, and whether or not you've taken (or are taking) a physics class, doing some of these calculations would be a great way to analyze your data.

http://hyperphysics.phy-astr.gsu.edu/hbase/pend.html#c1

As far as changing pitch types goes, I'm afraid I'm not enough of a baseball aficionado to know how the spins of the different pitches vary. Based on a bit of research I did, it looks like different kinds of pitches spin at different rates (but that there are other factors that determine how balls pitched in a certain way travel through the air). So, a first order approach would be to vary the spin rate of the ball by changing how many times you wind the pendulum string. In that case, your independent variable would be the number of times you wind the pendulum. You could measure how fast the ball spins, if you wanted, by counting how many times you see the stitching pass in a given amount of time. Then you can use your knowledge of how fast different pitches turn to qualitatively connect your results to different kinds of pitches.

Let me know if I can help with anything else!

This particular Project Idea is an "abbreviated" one, which is why the directions are not very complete. So, you'll need to fill in the details yourself; I think that makes a project more fun. But, it can also make things more difficult. Now, let's take a look at those two questions...

It will probably be best to hang the pendulum from something. You want gravity to be the only force acting on the pendulum, and if you hold it in your hand, you might introduce other forces. Be sure to keep the length of the pendulum constant.

The size of the cardboard grid will depend on how high the pendulum swings, because the height of pendulum is related to the horizontal displacement of the ball. You will want to release the pendulum from the same position for every test, and the pendulum will never swing higher the level you release it at. For pendulums, it is sometimes more helpful to release the pendulum at the same angle, as opposed to height, because the angle is easy to measure – just stick a protractor beneath the point where the string connects to whatever the pendulum is hanging from. Once you decide where you will release the pendulum, you can watch the pendulum swing to find out how big the cardboard needs to be. You could also do some simple trigonometry to calculate how big the cardboard piece needs to be for a given angular displacement.

This page from HyperPhysics describes some of the equations that describe pendulums. This particular experiment can be treated like a simple pendulum. Depending on your grade level, and whether or not you've taken (or are taking) a physics class, doing some of these calculations would be a great way to analyze your data.

http://hyperphysics.phy-astr.gsu.edu/hbase/pend.html#c1

As far as changing pitch types goes, I'm afraid I'm not enough of a baseball aficionado to know how the spins of the different pitches vary. Based on a bit of research I did, it looks like different kinds of pitches spin at different rates (but that there are other factors that determine how balls pitched in a certain way travel through the air). So, a first order approach would be to vary the spin rate of the ball by changing how many times you wind the pendulum string. In that case, your independent variable would be the number of times you wind the pendulum. You could measure how fast the ball spins, if you wanted, by counting how many times you see the stitching pass in a given amount of time. Then you can use your knowledge of how fast different pitches turn to qualitatively connect your results to different kinds of pitches.

Let me know if I can help with anything else!

All the best,

Terik

Terik