Question about the transfer of kinetic energy.

[Swa]

Assuming by bouncy ball it's meant that it's more elastic than the tennis ball it will be as follows:
Tennis ball undergoes less transformation so will spend less energy and transfer more energy in a shorter period of time. Bouncy ball spends more energy and transfers energy over a longer period of time. Part of the spending of energy is accumulated as potential energy as it transforms and is then released as kinetic energy exerting a force but over a longer period of time.

Tennis ball therefor transfers energy over a shorter period and also bounces back less so transfers more energy. Both these factors make it more likely to break the window.

 

[Knyro]

Hmm interesting thought experiment OP.

This is my reasoning:
> I think breaking the window will be more of a question of impulse as well kinetic energy
> They will both exert the same force on the window but the bouncy ball spends far less time in contact with the window so it exerts far more impulse on the window than the tennis ball. The bouncy ball is therefore more likely to break the window.

When it comes to kinetic energy:
> How much they bounce back has more to do with how efficient they are at converting kinetic energy to elastic energy and back again. i.e the tennis ball loses much more energy due to deformation, this isn't transferred to the window at all. The amount kinetic energy actually transferred to the window is probably quite close for both balls (hard to say without numbers).
> However because the bouncy ball delivers the energy in a much shorter time it is much more likely to break the window

Therefore 2, but because of impulse not force

 

[Knyro]

?

They were thrown at the same speed. OP says nothing about the speed of the balls after they hit the window, but it's easily deduced which ball leaves the window with the greater speed.

 

[FrankCastle]

When a ball is thrown at a window, the primary force acting on it is kinetic energy from the arm, and right before it is thrown, the ball possesses gravitational potential energy. (The gravitational potential energy is the arithmetic product of the ball's mass, the constant of acceleration due to gravity, and the ball's height: Ep = mgh.) When the ball is thrown, its potential energy is converted to kinetic energy (Ek = [1/2]mv2). When the ball hits the surface, its kinetic energy applies a "force of impact" on the surface, and the surface reacts with a nearly equal force of impact against the ball. Additionally, the surface and other materials involved will absorb some energy, leaving a little less energy to act upon the ball. The amount of energy absorbed by the surface depends on its nature and condition.

 

[Unhappy438]

They were thrown at the same speed. OP says nothing about the speed of the balls after they hit the window, but it's easily deduced which ball leaves the window with the greater speed.

Ok so first of all the initial debate was what speed the balls left at and not velocity after hitting the window. To work out the final velocity just before the ball hits the window vf^2 - vi^2 = 2ad is used. Now i need to assume here that the distance the balls were thrown from are the same seeing as the OP didn't specify. Resistance against the balls are the same due to the equal size and shape so now we have equal acceleration. Plug all that in and we have equal velocity just before the ball hits the window. Force exerted on the window is what will cause it to break so the speed the balls are travelling away from the window is irrelevant.

 

[droplet]

the bouncy ball changes direction in a shorter space of time, transferring its energy to the window more quickly. greater shock to the window - it will struggle to dissipate the energy more in the case of the bouncy ball. bouncy ball more likely to break window.

that's the answer. why is everyone still debating the question? it's such a simple problem, stop trying to overcomplicate it!

 

[Sinbad]

It's all about impulse. The time it takes for energy to be transferred.

So, what droplet said.

 

[Archer]

Force exerted on the window is what will cause it to break so the speed the balls are travelling away from the window is irrelevant.

And that force can be determined by..... looking at how fast the ball leaves.....

that's the answer. why is everyone still debating the question? it's such a simple problem, stop trying to overcomplicate it!

Discussed this for probably 40minutes with a colleague yesterday until he finally conceded

 

[droplet]

sorry. i was being just a little trollish earlier. i was hoping someone would bite and give me some armchair physics i could use as material on gullible people

 

[Swa]

that's the answer. why is everyone still debating the question? it's such a simple problem, stop trying to overcomplicate it!

Because it's not so simple. It's actually the tennis ball that transfers energy more quickly and it also transfers more energy.

 

[Unhappy438]

I think i get what you guys are trying to say , it basically comes down to elastic and inelastic collisions. The elastic (being the rubber ball) conserves more energy therefore resulting in a higher force against the window. The more inelastic tennis ball loses energy and results in less of a force against the window? Am i understanding this correctly?

 

[SaiyanZ]

Ok so first of all the initial debate was what speed the balls left at and not velocity after hitting the window. To work out the final velocity just before the ball hits the window vf^2 - vi^2 = 2ad is used. Now i need to assume here that the distance the balls were thrown from are the same seeing as the OP didn't specify. Resistance against the balls are the same due to the equal size and shape so now we have equal acceleration. Plug all that in and we have equal velocity just before the ball hits the window. Force exerted on the window is what will cause it to break so the speed the balls are travelling away from the window is irrelevant.

So if you also have another ball, this time metal and hollow so that it is the same size, shape and weight as the other two balls then it will be just as likely to break the window? Nope

The metal ball will have a much greater chance of breaking the window simply because it deforms less. The force will be applied to the window over a smaller surface area and over a shorter time period. This same methodology can be applied to the other two balls. The metal ball is the extreme case with a non-flexible ball.

 

[Knyro]

Ok so first of all the initial debate was what speed the balls left at and not velocity after hitting the window.

That's what everyone means by "left" i.e. after they left the window.

I think i get what you guys are trying to say , it basically comes down to elastic and inelastic collisions. The elastic (being the rubber ball) conserves more energy therefore resulting in a higher force against the window. The more inelastic tennis ball loses energy and results in less of a force against the window? Am i understanding this correctly?

Not quite. The time spent in contact with the window is the main factor. It's quite possible that the bouncy ball trasfers less energy to the window than the tennis ball, even with all of the tennis ball's innefficiencies. However because this transfer happens in a much shorter time it is more likely to break the window.

The bouncy ball has a higher impulse, not necessarily a larger force.

 

[scotty777]

Guys... You know it's not the 'energy', or the size of the ball etc... that breaks glass, it's the physical impact...

You could stand on a panel of glass, applying a massive force to it... And it won't break... However, drop a tiny lead weight in the middle, the impulse shatters the glass, not really the force. (ok, if I parked my car on glass, maybe the raw force itself will just make it fail... but lets leave that out).

Another example is punching a glass window, or hitting it with one of those little hammers. Your fist is absorbing a lot of the energy, meaning the impulse isn't so high. The little hammer is applying a lot of pressure, but also over a very brief period of time, so the impulse is massive.

Based on OP saying that the bouncing ball and tennis ball are equal, apart from the fact that the bouncing ball bouncing higher, this leads me to know one critical difference: The bouncing balls is able to generate a higher impulse than the tennis ball...

In essence, that means if we shot both balls at glass, slowly increasing the speed of the balls, I think the bouncing ball will break the glass first. Or, the bouncing ball requires less speed than the tennis ball to break the glass.

 

[Swa]

Guys... You know it's not the 'energy', or the size of the ball etc... that breaks glass, it's the physical impact...

You could stand on a panel of glass, applying a massive force to it... And it won't break... However, drop a tiny lead weight in the middle, the impulse shatters the glass, not really the force. (ok, if I parked my car on glass, maybe the raw force itself will just make it fail... but lets leave that out).

It won't break because you're NOT applying a massive force to it. This of course depends on the thickness of the glass and whether or not it's supported. In the case of dropping a lead weight on it the force is much more likely to shatter it because force = mass x speed. It's also not just force that matters but force over area.

Based on OP saying that the bouncing ball and tennis ball are equal, apart from the fact that the bouncing ball bouncing higher, this leads me to know one critical difference: The bouncing balls is able to generate a higher impulse than the tennis ball...

In essence, that means if we shot both balls at glass, slowly increasing the speed of the balls, I think the bouncing ball will break the glass first. Or, the bouncing ball requires less speed than the tennis ball to break the glass.

Wrong. The tennis ball transforms less so transfers energy over a smaller area and over a shorter time than the bouncy ball that "hugs" the glass and transfers energy over a larger area and over a longer time.

The deformation of the bouncy ball also spends more energy so there's less to transfer. Think of an F1 racing car. On the moment of impact it uses up a lot of energy by falling apart and deforming (the bouncy ball). If it were solidly built more energy would be transferred to the driver (the tennis ball).


I still want to know why the OP wants to know. Did he and his friend throw balls at a window and now want to know who broke it? Sorry Humberto you have to cough up.

 

[zippy]

Isn't the bouncy ball more dense than the tennis ball and there actually needs more kinetic energy to launch it at a window? I think we need more info about the physical properties of each to determine :

1. How much kinetic energy does each ball have as they leave the arm of thrower?
2. How much energy is lost in flight due to size and friction if surface with the air.
3. How much kinetic energy is absorbed by each ball at the moment of impact due to each balls physical properties.

 

[scotty777]

It won't break because you're NOT applying a massive force to it. This of course depends on the thickness of the glass and whether or not it's supported. In the case of dropping a lead weight on it the force is much more likely to shatter it because force = mass x speed. It's also not just force that matters but force over area.


Wrong. The tennis ball transforms less so transfers energy over a smaller area and over a shorter time than the bouncy ball that "hugs" the glass and transfers energy over a larger area and over a longer time.

The deformation of the bouncy ball also spends more energy so there's less to transfer. Think of an F1 racing car. On the moment of impact it uses up a lot of energy by falling apart and deforming (the bouncy ball). If it were solidly built more energy would be transferred to the driver (the tennis ball).


I still want to know why the OP wants to know. Did he and his friend throw balls at a window and now want to know who broke it? Sorry Humberto you have to cough up.

Wait, I don't understand. Have you played with a bouncing ball? It is much firmer than a tennis ball.

If anything, the tennis ball squashes and 'hugs' the surface it impact.

Also, looking at these two videos, the balls travel at the same speed (the bouncing ball actually faster) given the bouncing ball is recorded @ 2500FPS, the tennis ball @ 2000FPS.

http://www.youtube.com/watch?v=3jI57WMOzbU
http://www.youtube.com/watch?v=0KfD-v23isA

The tennis ball is clearly deforming more... The more things deform, the more energy is transferred to heat... The impact time will be longer in the tennis balls time, making the impulse much smaller.

Another example of this is the famous MythBusters Chicken cannon, where they proved that freezing the chickens made more damage than regular chickens... Same thing with bouncing ball vs tennis applies... The 'faster' the impact, the more likely glass will break.

 

[Swa]

Wait, I don't understand. Have you played with a bouncing ball? It is much firmer than a tennis ball.

If anything, the tennis ball squashes and 'hugs' the surface it impact.

I think you're confused here. Assuming by bouncy he means more bouncy than the tennis ball it must be less firmer. I played with lots of tennis balls before and they are all pretty firm. What definition of firm are you using? Does it mean less capable of transformation?

Also, looking at these two videos, the balls travel at the same speed (the bouncing ball actually faster) given the bouncing ball is recorded @ 2500FPS, the tennis ball @ 2000FPS.

http://www.youtube.com/watch?v=3jI57WMOzbU
http://www.youtube.com/watch?v=0KfD-v23isA

The tennis ball is clearly deforming more... The more things deform, the more energy is transferred to heat... The impact time will be longer in the tennis balls time, making the impulse much smaller.

It's not very clear how fast each ball was traveling before it hit. The scale of the videos need to be the same and it needs to be known if the 'bouncy ball' isn't actually firmer than the tennis ball.

I just noticed a discrepancy in what the OP says though. If the balls are of equal weight then the tennis ball is likely larger as it's hollow. It's not size that matters though. If they are of equal size then the tennis ball would likely be lighter and less likely to break the window. I'm assuming that they are of equal size and weight.

 

[scotty777]

I think you're confused here. Assuming by bouncy he means more bouncy than the tennis ball it must be less firmer. I played with lots of tennis balls before and they are all pretty firm. What definition of firm are you using? Does it mean less capable of transformation?


It's not very clear how fast each ball was traveling before it hit. The scale of the videos need to be the same and it needs to be known if the 'bouncy ball' isn't actually firmer than the tennis ball.

I just noticed a discrepancy in what the OP says though. If the balls are of equal weight then the tennis ball is likely larger as it's hollow. It's not size that matters though. If they are of equal size then the tennis ball would likely be lighter and less likely to break the window. I'm assuming that they are of equal size and weight.

I believe there is a problem in the question asked, as it is indeed impossible to meet all requirments.

However, I will use one in fact to prove my point, bouncy balls are solid rubber balls, while tennis balls are hollow rubber balls. So they can ever be same size or same mass... But if same mass approach is taken, ie: same kinetic energy, then I still think the bouncy ball will break the glass because of one simple property:
Rubber has an elastic deformation-> pretty good for energy transfer

Air is a good damper... So much so, it converts kinetic energy into sound and heat. Air is inside the tennis ball.
Tennis balls are also under 'low pressure', allowing for a lot of deformation, but also a massive pressure to form inside the ball, creating lots of heat and sound... This means less kinetic energy on impact... But this is examining the inner workings, all is irrelevant, since:

OP Said: bouncy ball bounces higher! Thus much more energy is transferred ( conversed actually), than the tennis ball. There's more energy loses in the tennis ball clearly, these loses are in the form of heat and sound (usually, although, quantum tunnelling can lose the whole ball ). From this, it can be said that the ball exerts more pressure than the tennis ball.

 

[Knyro]

I assumed some new space age bouncy ball material that would allow the balls to be the same size

Guys... You know it's not the 'energy', or the size of the ball etc... that breaks glass, it's the physical impact...

The energy is not irrelevant. Even looking at it from a pure energy perspective you should be able to conclude that the bouncy ball is more likely to shatter the glass.

>The bouncy ball imparts its energy to the window faster
>The individual particles that make up the glass recieve kinetic energy in a shorter amount of time. i.e. they accelerate faster
> They will probably recieve energy at a much faster rate than they are losing it to collisions with other particles
>Because now the particles where the bouncy ball hit are now flying in all directions very fast they are more likely to break the bonds between them.
> The window is more likely to break

Contrast this to the particles that recieve kinetic energy slower from the tennis ball

> The energy of the individual particles is less likely to reach some critical point because they are already losing energy when colliding with other particles, even while the tennis ball is still imparting energy, albeit more slowly than the bouncy ball
> They are less likely to break the bonds between them and fly apart
> The window is less likely to break