What is the best method to calculate the force of a baseball swing?

[danago]

Hey. For my physics class, we are required to do whatever it takes to calculate the force one can apply with the swing of a baseball bat. We are given a ticker timer, a stopwatch and a meter ruler (to simulate a baseball bat). We can use other things if we wish, such as an actual baseball bat etc, but avaliable equipment is limited.

What we have done so far is taken a few time measurements of how long a swing takes, from the moment the bat begins moving, until the moment it strikes the ball. We recorded an average of 36ms. We then used some of the long ribbon paper from the ticker timer, and, keeping it tense, measured the total distance the tip of the bat moves during its motion until it strikes the ball. It was approximately 1.64m

With these values (Vi=0, s=1.64, t=0.36), we then calculated the average acceleration as ~25.3 m/s/s, which we originally thought that we could use to calculate the force the bat will strike with. However, now that we have thought more, we are doubtful about our results, since the acceleration is more than likely not constant, so the force therefore throughout the swing won't be constant.

We are now trying to think of new ways to complete this investigation. If anyone has ideas, please post, all help greatly appreciated.

Thanks,
Dan.

 

[Galileo]

It will be difficult measuring the (average) force the bat exerts on the ball. It's actually the impulse (average force times the duration the bat is in contact with the ball) that is important in determining the momentum delivered to the ball.
If the baseball is soft, it will deform greatly upon hitting the bat. This will lengthen the duration of contact, but decrease the average force on the ball (like a crumple zone on a car).
A very hard ball which does not deform much will endure a much greater force from the same batswing, but the contact duration is also very short.

 

[danago]

Hmmmm...ok...how do we calculate this impulse though? And I am not entirely sure how to apply it. Would i estimate a change in momentum, by estimating the velocity change of the ball upon hitting the bat, and then divide this by an estimated contact time?

 

[Galileo]

Uhm, that's a lot of estimating. If you know how fast the ball goes after impact (assuming it's initially at rest), you can find the momentum change because you know the mass of the ball.
If you can't find an easy way to directly measure the velocity of the ball after impact, try deducing it from the distance traveled before it hits the ground.

But yeah, with the equipment given, I guess the best you can do is estimate the contact time.

 

[danago]

Apparently air resistance has quite a large impact on the distance the ball will travel before coming to rest. I have yet to learn about including air resistance in calculations. I've also heard it can be quite complex. How inaccurate would my calculations be without the inclusion of drag?

 

[Farsight]

Could do something you can measure better, and then compare with swinging the bat? Off the top of my head, maybe you could use the baseball bat to hammer a stake into the ground. Then you could rig up something that drops a known weight a known distance to hammer the same stake into the same ground by the same amount. Maybe there's something simpler, like striking a heavy ball on a pendulum?

 

[danago]

hmmm i see what you're saying. So i could take the bat and hit a nail or something into the ground with a single strike, and measure the penetration. Then do the same again with an object of known mass from like 1m high, then calculate the force it applies to the nail using Newtons F=ma formula, then compare the penetration of the bat to that of the falling object? So if the bat hit the nail 3cm into the ground, and a mass of 5kg did 1cm, i could approximate that the force of the bat is 3 times that of the falling mass, which would mean it applies approximately 147N?

 

[Farsight]

In that example you'd be better off adjusting the weight or the height until you get the same 3cm penetration. It cuts out a variable.

It occurs to me that maybe they want you to see how far you can hit the ball and work back from that.

 

[tim_lou]

I think the question is a little bit vague... do you mean the maximum force a human can apply to a baseball bat (at one instant?) ? or the maximum force the baseball bat can apply to an object (at one instant)?

if it is human on a baseball bat... you can try to swing the bat around and around and do something with centripetal force... But that will only get you the average (sort of). I doubt you can find the "maximum force" anyway.

 

[danago]

We need to find the force the baseball bat strikes the ball with.

 

[Farsight]

OK. You stand 10m away from a wall, somebody pitches the ball, and WHACK... POCK. You use the stopwatch to find out how long the ball took to travel the distance. Then you work out the speed of the ball, and knowing its weight you work out its kinetic energy in Joules. Kinetic energy equates to work equates to force times distance, so to work out the force properly you have to work out the distance traveled by bat and ball while in contact. I'm not sure about that. Hmmn. Maybe it's something to do with how long that WHACK lasted.

http://www.uwsp.edu/cnr/wcee/keep/Mod1/Whatis/PeoplePower.htm

 

[danago]

Hmmm that's another option. Ill definitely suggest that to the other members in my group. Thanks very much for posting.