# Naked Science Forum

## Non Life Sciences => Technology => Topic started by: benm on 15/04/2019 14:27:43

Title: Where is the sweet spot on a baseball bat?
Post by: benm on 15/04/2019 14:27:43
Ethan has a question about sporting goods?

Where is the sweet spot on a baseball bat

Won't anyone be a sport and help him out?
Title: Re: Where is the sweet spot on a baseball bat?
Post by: Janus on 15/04/2019 15:43:06
The sweet spot on a baseball bat corresponds with a vibration "node".  When the bat is struck at any spot, vibrations travel through the bat at the speed of sound for the bat's material.   If the Bat is struck at the node, these vibrations, due to the way they trave, tend to cancel each other out and the bat, as a whole, doen't vibrate as much.  Energy that goes into vibration of the bat is not transferred to ball, So having the ball hit the Sweet spot or node results in more the energy of impact being transferred to the ball.
To find the sweet spot, let the bat hang downward while you hold it lightly by the handle.  Have someone else tap the bat with another object, moving up and down the length of the bat as they do so.   When they reach the sweet spot, you won't feel any vibration in the handle.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: alancalverd on 15/04/2019 19:11:24
It's at the point where a simple pendulum (small heavy weight on a light string)  swings at the same rate as the bat held by the end of the handle. Same applies to cricket bats and tennis racquets.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: Bored chemist on 15/04/2019 19:16:49
How close is it to the Centre of gravity of the bat?
(I know it's not the same thing, but the  CoG is easy to find.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: alancalverd on 16/04/2019 10:04:22
It's a bit more complicated as you are looking for the point of dynamic (Σmr2) rather than static (Σmr) balance. The pendulum method certainly works well for baseball and cricket bats. I think the CG of a tennis racquet is on the wood, not the middle of the stringing.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: flummoxed on 16/04/2019 13:59:13
The sweet spot on a baseball bat corresponds with a vibration "node".  When the bat is struck at any spot, vibrations travel through the bat at the speed of sound for the bat's material.   If the Bat is struck at the node, these vibrations, due to the way they trave, tend to cancel each other out and the bat, as a whole, doen't vibrate as much.  Energy that goes into vibration of the bat is not transferred to ball, So having the ball hit the Sweet spot or node results in more the energy of impact being transferred to the ball.
To find the sweet spot, let the bat hang downward while you hold it lightly by the handle.  Have someone else tap the bat with another object, moving up and down the length of the bat as they do so.   When they reach the sweet spot, you won't feel any vibration in the handle.

Here is an mildly amusing utube on the sweet spot with a demo tapping the bat to find the sweet spot.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: Bored chemist on 16/04/2019 18:03:40
It's a bit more complicated as you are looking for the point of dynamic (Σmr2) rather than static (Σmr) balance. The pendulum method certainly works well for baseball and cricket bats. I think the CG of a tennis racquet is on the wood, not the middle of the stringing.
I'm pretty sure the "same a a pendulum" method can't work reliably.
The "sweet spot" is defined (usually) in terms of vibration. That's a function of stiffness and mass.
The pendulum point or CoG would be dependent on mass and length.
The stiffness of the stringing of a tennis racket is clearly much lower than the stiffness of the wood (or whatever) frame.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: alancalverd on 16/04/2019 18:22:59
Try it and see! I remember doing the experiment in my schooldays and being impressed with the result.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: Bored chemist on 16/04/2019 18:27:59
I Suspect that any of the methods would give pretty close to identical answers- far more accurately than I could rely on hitting a ball.
But I think the CoG method has the advantage of being easy, albeit probably the least reliable.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: flummoxed on 16/04/2019 19:00:14
It's a bit more complicated as you are looking for the point of dynamic (Σmr2) rather than static (Σmr) balance. The pendulum method certainly works well for baseball and cricket bats. I think the CG of a tennis racquet is on the wood, not the middle of the stringing.
I'm pretty sure the "same a a pendulum" method can't work reliably.
The "sweet spot" is defined (usually) in terms of vibration. That's a function of stiffness and mass.
The pendulum point or CoG would be dependent on mass and length.
The stiffness of the stringing of a tennis racket is clearly much lower than the stiffness of the wood (or whatever) frame.

You need to find the null spot in the vibration, along the bat. It is typically a couple of inches or more from the end of the bat. Janus explained this best above. A baseball bat is a lot different to a tennis racket. If you hit the ball in the wrong spot along the bat, less energy is transferred to the ball due to vibrations along the bat. If you hit the sweet point/null point along the bat all the energy is transferred to the ball, as explained also in the video. The Null point depends on shape and material used in the bat. The CoG appears to be nowhere near the detected sweet point in the video.
Title: Re: Where is the sweet spot on a baseball bat?
Post by: Stephbaker on 13/05/2019 08:53:25
it's really great to see that so many people know about it  ;D ;D