# Bouncing time



## mikeydt1 (Mar 25, 2021)

which will bounce the highest a ball of glass or a ball of rubber?


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## Paulbreen (Mar 25, 2021)

I had to think about that one a bit Mikey but my old physics lessons at school clicked in, the glass I’m sure because of lack of deformation


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## Docb (Mar 25, 2021)

Curious wording.  Is it the same as asking - which will bounce highest, a glass ball or a rubber ball?


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## mikeydt1 (Mar 25, 2021)

Paul i will let Doc have a think about this then get back with the answer


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## Ditto (Mar 25, 2021)

A ball full of rubber would bounce higher as the ball full of glass would be heavier?


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## mikeydt1 (Mar 25, 2021)

when i use to play with my little dog i used to chuck a rubber ball against a wall and my dog would try and catch it don't think a glass ball would of enjoyed the same impact


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## Docb (Mar 25, 2021)

If you are asking whether a solid ball made from rubber, would rebound to a greater or lesser height than a solid ball made from glass when dropped from the same height onto the same surface, then the rubber ball would rebound the highest. That's because the rebound height, assuming there is no plastic deformation of the ball or that the ball does not break, is dependent on the elastic modulus of the material.  Rubber has a lower elastic modulus than glass and will consequently rebound to a greater height.

If you are asking something different, then the answer might be different.


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## mikeydt1 (Mar 25, 2021)

right according to our Mr google Paul has the correct answer i will let him explain the physics as all i get is the question and answer.  if i was in a pub on a Friday night think i would of made a mad dash for the door.    do love all the answers to this one and wonder what google theory is.


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## Amity Island (Mar 25, 2021)

mikeydt1 said:


> which will bounce the highest a ball of glass or a ball of rubber?


Bounce off what?


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## Robin (Mar 25, 2021)

Amity Island said:


> Bounce off what?


I was thinking, it depends what it’s landing on. 
Interesting discussion here, which takes that into account. (it’s a bit beyond me, science wise)








						Why the rubber ball bounced higher than the glass ball?
					

For a teaching degree we did the following experiment:  Drop a rubber and a glass ball of approx. same size from approx. same height onto laminate flooring.   As we expected, the rubber ball bounced




					physics.stackexchange.com


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## Docb (Mar 25, 2021)

mikeydt1 said:


> right according to our Mr google Paul has the correct answer i will let him explain the physics as all i get is the question and answer.  if i was in a pub on a Friday night think i would of made a mad dash for the door.    do love all the answers to this one and wonder what google theory is.



Hope he can explain it.  

The Young's Modulus of rubbers are generally in the range 0.01 - .1 MPa,  whereas glasses are in the range 50-90 MPa. Assuming the stresses induced in the ball are the same because they are dropped from the same height onto the same surface and both balls are homogenous and solid, then a greater strain will be induced in rubber ball and as a consequence it will rebound the further as the strain is recovered.  At least that's how I understand the mechanics of it.

Happy to be shown the error of my ways.


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## Paulbreen (Mar 25, 2021)

I think It’s to do with the deformation of the ball when it hits the floor, a rubber ball will obviously deform quite a lot which will absorb some of the motion whereas the glass ball will not deform so it will carry it’s motion throughout the bounce, I didn’t Google it yet but will get a look after work


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## Docb (Mar 25, 2021)

It's the deformation, provided it is elastic, that causes the rebound.  A ball of plasticine for example would not bounce at all because the deformation would be plastic.  The more elastic deformation, the more the rebound.  Imagine a snooker table with glass or wooden cushions instead of rubber. Any ball hitting it would hardly bounce at all and half the shots the pro's make would not be possible!

I am assuming the mikeydt1 has found something which gives the "wrong" answer by some odd interpretation of the question. Its why I have been very precise in defining the parameters in my answers.


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## Paulbreen (Mar 25, 2021)

Well I did check it and apparently I was correct according to Google 
Why Glass and Steel Bounce Better Than Rubber​When a rubber ball hits a surface, it compresses and deforms before returning to its original shape. Quite a lot of energy is lost in this process. Although it is not a crystal like its chemical relative, quartz (SiO2), glass is rigid and does not deform much when it strikes a surface. Most of the energy of the impact returns to the glass.


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## mikeydt1 (Mar 26, 2021)

when a rubber ball hits a hard surface the rubber ball compresses and deforms before it returns to its original state.

that is the correct theory to the quiz question which Paul got right, well done with your physics. 

question and answer from sciencenotes.org


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## Docb (Mar 26, 2021)

Oh dear, all my education, all those years doing complicated sums, trashed by the internet.


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## Paulbreen (Mar 26, 2021)

Thank you Mikey. Here’s a quick riddle for you to get the grey matter moving this morning 
*What can be driven although it doesn’t have wheels, sliced but stays whole?*


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## Paulbreen (Mar 26, 2021)

Docb said:


> Oh dear, all my education, all those years doing complicated sums, trashed by the internet.


I remember a very flamboyant physics teacher I had at school, who lived for actual live experiments and I had a vague recollection of this very experiment, benefit of a British forces Schools education, we have many weird teachers over the years


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## Docb (Mar 26, 2021)

Were the balls of equal diameter or equal weight?


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## Paulbreen (Mar 26, 2021)

Hey Doc, according to the bumf I read they were the same size, it also mentioned that a steel ball would bounce more than the rubber one too. I wonder which would bounce more the steel or the glass


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## Docb (Mar 26, 2021)

So if they were equal size they would be of different weights. The steel ball would have a higher kinetic energy on impact and I would imagine that would have some effect on the rebound height. The answer may be different if the balls were of the same weight but different sizes.  May also be different if the balls were of the same size but the lighter ball was loaded with lead to make it the same weight as the other.  

You would also get different answers if by "ball" you mean a hollow sphere like the balls used in sports.  You might then expect the internal pressure to come into play.  A pumped up football for example bounces much higher than a flat one.

More complicated than you might think.  My science teachers were not flamboyant but they did instil the idea that establishing the boundaries to which an experimental result can be applied is a good idea.


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## Paulbreen (Mar 26, 2021)

Well I managed 4 good science based a-levels with the flamboyant teachers so their style apparently worked, and I did enjoy those lessons very much including maths which I detested until my fourth year until the teacher made it such an interesting lesson.
It looks like we’re going to have to find some steel glass and rubber balls and do the experiment, I’m going on Amazon Typ see what I can find lol


Docb said:


> So if they were equal size they would be of different weights. The steel ball would have a higher kinetic energy on impact and I would imagine that would have some effect on the rebound height. The answer may be different if the balls were of the same weight but different sizes.  May also be different if the balls were of the same size but the lighter ball was loaded with lead to make it the same weight as the other.
> 
> You would also get different answers if by "ball" you mean a hollow sphere like the balls used in sports.  You might then expect the internal pressure to come into play.  A pumped up football for example bounces much higher than a flat one.
> 
> More complicated than you might think.  My science teachers were not flamboyant but they did instil the idea that establishing the boundaries to which an experimental result can be applied is a good idea.


another thought springs to mind Doc, what’s the floor material, if it’s concrete or if it’s something softer like the material they use in children’s play areas the rubber ball my bounce higher


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## Docb (Mar 26, 2021)

Quite right Paul, all the theory and the oversimplifications assume a hard surface.

My view of the world of science changed most during my PhD studies under the guidance of Eric Holmes, my supervisor.  He believed that asking the right question was more valuable than producing smart answers. A great man, totally forgotten.


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