Cork Bats and Physics

Wicked Pilot · Post by **Wicked Pilot** » 2003-06-05 12:01pm

OK, I'm sure we're all familiar with what's going on now a days with Sammy Sosa. My question: does it really matter? Does putting cork in a bat really help? The velocity and therefore the distance a ball will travel after being hit depends on the amount of momentum given to it after it's collision with the bat. This in turn depends on the bat's momentum. This should not change regardless of the bat's mass. A corked bat will swing faster, but with less mass, therefore it's momentum will be the same as the uncorked bat that is slower, but has more mass. So what's the big deal, is there some kind of collision physics that I'm not thinking of here, or are MLB players just dumbasses?

Any and all physics and engineering experts feel free to respond.

Joe Richter · Post by **Joe Richter** » 2003-06-05 12:10pm

Its to do with the elasticity of the collision, and the efficiency of the transfer of momentum.

kojikun · Post by **kojikun** » 2003-06-05 12:10pm

corking does two things:

1 it prevents compressino in the ball (which drains energy shortens its flight) by allowing the bat to e isted(which is silly because metal bats compress so much better)

and 2 it makes the bat easier to swing (increasing the speed you can swing it at).

The second effect is the one doing the most. A 1 kg bat moving at 50kph has a KE of 2500J whereas a 0.5 kg bat moving at 75kph has a momentum of 2800J.

Obviously its better to have a lighter bat moving faster, atleast in this case, because the ball will go faster and farther.

TrailerParkJawa · Post by **TrailerParkJawa** » 2003-06-05 01:33pm

Im no good at the physics stuff, but people on the radio where saying it only adds like 5-10 ft to the distance you can hit the ball. I dont think that matters much for Sosa, but its still not allowed. I dont follow baseball, so I dont have much on an opinion either way.

neoolong · Post by **neoolong** » 2003-06-05 02:03pm

TrailerParkJawa wrote:Im no good at the physics stuff, but people on the radio where saying it only adds like 5-10 ft to the distance you can hit the ball. I dont think that matters much for Sosa, but its still not allowed. I dont follow baseball, so I dont have much on an opinion either way.

Which can matter if a home run only barely makes it over the fence. But still, it's cheating if nobody else is allowed to do it.

RedImperator · Post by **RedImperator** » 2003-06-05 02:15pm

TrailerParkJawa wrote:Im no good at the physics stuff, but people on the radio where saying it only adds like 5-10 ft to the distance you can hit the ball. I dont think that matters much for Sosa, but its still not allowed. I dont follow baseball, so I dont have much on an opinion either way.

5-10 feet can be the difference between a home run or an easy catch at the warning track. It doesn't give the kind of distance an aluminum bat does, but it's enough for an unfair advantage in a game where most critical plays are a matter of inches.

Wicked Pilot · Post by **Wicked Pilot** » 2003-06-05 02:26pm

kojikun wrote:corking does two things:
1 it prevents compression in the ball (which drains energy shortens its flight) by allowing the bat to e isted(which is silly because metal bats compress so much better)

That makes sense.

and 2 it makes the bat easier to swing (increasing the speed you can swing it at).

The second effect is the one doing the most. A 1 kg bat moving at 50kph has a KE of 2500J whereas a 0.5 kg bat moving at 75kph has a momentum of 2800J.

Obviously its better to have a lighter bat moving faster, atleast in this case, because the ball will go faster and farther.

If you make the bat twice as light, then you will swing it twice as fast, giving it the same momentum. It may have more kinetic energy, but KE is not always conserved and therefore does not enter into the equation.

Wicked Pilot · Post by **Wicked Pilot** » 2003-06-05 02:29pm

Joe Richter wrote:Its to do with the elasticity of the collision,

But how?

and the efficiency of the transfer of momentum.

How would the transfer of momentum lose efficiency? Conservation of momentum is one of the most solid laws of science.

EmperorChrostas the Cruel · Post by **EmperorChrostas the Cruel** » 2003-06-05 03:18pm

When compresion and expantion take place, some of the stored energy becomes heat, and is "lost." As opposed to direct transfer, like a pushrod compared to a spring. They both transfer kinetic energy, but the spring heates up.So does the pushrod, but not nearly as much.
Compressive heat, as compared to twisting. From my hot rod days, I can tell you that the springs on race cars get HOT, from all that twisting and flexing. The ball joints don't and get the same amount of force applied to them.

Also, the lighter bat, swinging faster, increases the ability to HIT the ball, in the first place! NOT an insignificant bonus. The 10/15 feet of extra travel is great, (more homers!)but simply connecting with ball more will, bring in more runs, get more base hits, and advance baserunners.
In baseball, base hits, and runs batted in, win much more game than home runs.(although some RBIs are from home runs.)Contrary to popular opinion.
Everyone remembers the home runs, but base hits and RBIs win games, more often than not. (many games have NO home runs.)

Wicked Pilot · Post by **Wicked Pilot** » 2003-06-05 03:59pm

Emperor Chrostas the Crue wrote: Also, the lighter bat, swinging faster, increases the ability to HIT the ball, in the first place! NOT an insignificant bonus.

Now this makes sense.

EmperorChrostas the Cruel · Post by **EmperorChrostas the Cruel** » 2003-06-05 05:39pm

Baseball bats of the pros are made as light as possible, just for this reason. The kicker is, if you make it too light,, (by making it thinner, or tubular) it breaks. Drilling the center of the bat, and leaving it hollow, I believe is legal, but not done for structural reasons. CRACK. I have seen folks dent aluminum bats on fast pitches at the batting cages. Wood cracks, when tubular.

Hell, they bust solid bats all the time.These are the best of the best, baseball wise, and these guys are strong.

Durandal · Post by **Durandal** » 2003-06-05 08:01pm

Wicked Pilot wrote:
Joe Richter wrote:Its to do with the elasticity of the collision,
But how?

Think about dropping a raquet ball on a concrete floor as opposed to a baseball. What does it mean when an object bounces? It means that the object hit the ground with sufficient force that the reactionary force supplied by Newton's third law was enough to throw the object back up into the air.

What facilitates the raquet ball to bounce higher than the baseball if both hit the ground with equal force (neglect the mass differential)? The raquet ball is made of an elastic material, and it is therefore more conducive to compression. Elastic materials always want to return to their original form (witness a stretched rubber band), and they want to do so very quickly. So, as the raquet ball decompresses, the expansion of the compressed end will give an extra kick to it. Obviously, the more compressed the elastic material, the bigger the kick from its expansion.

Now, let's apply this to a corked bat. Since the bat is more elastic, it will undergo a slight amount of compression during the collision. Now, imagine the finite instance where the ball hits the bat, and the ball's velocity is zero. Then the momentum is transferred in a finite interval, creating a force. However, the expansion of the bat will reduce the time interval that the bat and ball are in contact and grant an extra kick of momentum to the ball. This results in the same momentum transfer in less time, creating a larger force, resulting in greater acceleration. Coupled with the extra kick from the decompression of the bat, the result is that the ball goes farther in less time.

How would the transfer of momentum lose efficiency? Conservation of momentum is one of the most solid laws of science.

Because the momentum transfer between the bat and the ball isn't perfect. The bat keeps moving after the collision.

SyntaxVorlon · Post by **SyntaxVorlon** » 2003-06-05 08:38pm

Wicked Pilot wrote:
Joe Richter wrote:Its to do with the elasticity of the collision,
But how?

and the efficiency of the transfer of momentum.
How would the transfer of momentum lose efficiency? Conservation of momentum is one of the most solid laws of science.

CoM is compensated as it always is, you see elasticity is the ability of an object to retain its form and reflect or absorb energy kinetically.
Like that little desk toy with the bouncing metal balls, because metal is highly elastic you can drop a ball from one side and the other side bounces away.

If an object hits another one of equal but low elasticity, they will just stop, because all the energy has been frittered away in nonKinetic activities such as warpage, sound, heat, etc.

The only pure elastic collisions happen mostly in vacuums between to speeding atoms. That way energy isn't lost to sound heat or anything else.

In the case of baseball bats, as kojikun pointed out, elasticity isn't the issue. Because metal is more elastic than cork.

DPDarkPrimus · Post by **DPDarkPrimus** » 2003-06-05 10:04pm

Hey, anyone got a pic of Sosa when his helmet got shattered by that fastball? That would make a great poke pic.

Sriad · Post by **Sriad** » 2003-06-06 12:06am

Wicked Pilot wrote:If you make the bat twice as light, then you will swing it twice as fast, giving it the same momentum. It may have more kinetic energy, but KE is not always conserved and therefore does not enter into the equation.

Not true: KE=.5*mv^2 That's velocity squared. If you have something half as light going twice as fast, then it will have twice the KE of the original object.

But in this case the point that Emperor Chrostas brought up is probably most important, that having a light bat will let you hit the ball more often. Mostly just trying to correct some physics.

Though in this case we'd be dealing with rotational KE, which is a whole different kettle of fish. That I don't want to get into. But the same relationship stands; it's better to have half the mass and twice the velocity if you want more KE.

Wicked Pilot · Post by **Wicked Pilot** » 2003-06-06 12:54pm

Sriad wrote:Not true: KE=.5*mv^2 That's velocity squared. If you have something half as light going twice as fast, then it will have twice the KE of the original object.

Momentum is simply mass times velocity and is what is used for collisions. KE is not always conserved and therefore is not used.

Though in this case we'd be dealing with rotational KE, which is a whole different kettle of fish. That I don't want to get into. But the same relationship stands; it's better to have half the mass and twice the velocity if you want more KE.

We're not dealing with KE at all here. How many times do I have to explain it to you people than in collisions we use momentum to calculate outcomes because the system's total momentum is conserved, while KE is not.

SyntaxVorlon · Post by **SyntaxVorlon** » 2003-06-06 01:16pm

Let's put it this way:
mv(ball)+mv(bat)=mv(ball after)+mv(bat after)
100km/h pitch with a .2 kg ball(I don't know the real mass)+75km/h bat of 2-3 kg - 60km/h bat with a mass of 2-3 kg = the ball's momentum after the hit.
If bat is lighter and faster it can have a higher momentum, transfering more energy and getting that ball to go further.

Patrick Degan · Post by **Patrick Degan** » 2003-06-08 04:27am

The simple explanation is all a matter of weight and momentum.

The true secret of power-batting is not the size or weight of the bat but how fast the batter connects with the ball. The lighter the bat, the faster the swing. The colleges use aluminium bats from sheer economy; longer service lives as opposed to wood. However, the aluminium bats have also skewed college baseball heavily in favour of the offense, with double-digit scores quite common —which is why the professional game will never adopt aluminium or graphite bats due to the inevitable damage to the stastics which would ensue.

The corked bat, being lighter, gives the hitter the advantage of an artifically faster swing over regulation bats of similar design, which is why it is illegal for game-play. There was a big scandal involving a Yankees playter using a corked bat in several games in one season during the 80s, if memory serves.

Fortunately, it appears that in Mr. Sosa's case, his use of an illegal bat was accidental. The league office accepted his appeal and rescinded his suspension.