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Author Topic: Bouncing a ball on the moon.  (Read 11199 times)

paul.fr

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Bouncing a ball on the moon.
« on: 24/04/2007 23:34:06 »
Will a bouncy ball bounce for longer and higher on the moon than on the earth?


 

Offline neilep

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Bouncing a ball on the moon.
« Reply #1 on: 24/04/2007 23:38:55 »
Excellent question Paul...Me thinks me knows the answer but I'll leave it be.

Incidentally...you made me think of a question I asked a while back about jumping to your death on the moon...it's HERE if you're interested...it's kind of related !!
 

Offline Seany

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Bouncing a ball on the moon.
« Reply #2 on: 24/04/2007 23:40:46 »
Well, it will definitely bounce for longer. And it will probably bounce higher, because there is less force acting downwards on the ball.
 

paul.fr

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Bouncing a ball on the moon.
« Reply #3 on: 24/04/2007 23:44:23 »
Thanks for the link, neil.
 

Offline Batroost

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Bouncing a ball on the moon.
« Reply #4 on: 24/04/2007 23:48:38 »
If you drop a ball on the moon it will bounce exactly as high as it would on the earth - as you've only given it the potential energy of the height it was dropped from. A perfectly elastic ball would bounce back to the hieght from which it was dropped regardless of the local strength of gravity.

If on the other hand you throw the ball towards the ground so that it's kinetic energy is a high value - the same on the earth and the moon - then, roughly speaking the ball would bounce six times higher on the moon than it would on the earth.
 

Offline daveshorts

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Bouncing a ball on the moon.
« Reply #5 on: 25/04/2007 10:06:16 »
Yes and it will bounce for longer because there will be the same number and height of bounces as on earth, but beacuse it will fall slower so each bounce will take longer.
 

Offline lightarrow

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« Reply #6 on: 25/04/2007 10:55:12 »
Yes and it will bounce for longer because there will be the same number and height of bounces as on earth, but beacuse it will fall slower so each bounce will take longer.
There would be a greater number of bounces, actually, because of no air...
 

Offline Batroost

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Bouncing a ball on the moon.
« Reply #7 on: 25/04/2007 17:39:26 »
Quote
There would be a greater number of bounces, actually, because of no air...

Imagine you tried the expermient inside a sealed (fully evacuated) container on the earth. This negates any effect of air pressure. The ball will still stop bouncing because it is not having perfectly elastic collisions with the ground i.e. some of the work done in compressing the ball is lost as heat.

But, the collisions between the ball and the surface on the moon are slower. Might this mean that they are more elastic, with less heat generated/energy lost (a bit of a guess this)? In which case the ball would complete more bounces before coming to rest on the moon than on the earth.
 

Offline ukmicky

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Bouncing a ball on the moon.
« Reply #8 on: 25/04/2007 18:42:51 »
However as the moon has no atmosphere the air inside the ball would apply more pressure to the skin of the ball due to the lack of  Atmospheric pressure making it more rigid and reducing its ability to bounce. :)
« Last Edit: 25/04/2007 18:45:41 by ukmicky »
 

Offline Bored chemist

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Bouncing a ball on the moon.
« Reply #9 on: 25/04/2007 18:54:46 »
Not all balls are full of air.
The internal molecular vibrations that correspond to heat are much faster than the "bounce". I don't think the 6 fold drop in gravity would make any difference to the energy transfer.
BTW, how many bounces does it take before the ball actually stops?
 

Offline ukmicky

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Bouncing a ball on the moon.
« Reply #10 on: 25/04/2007 19:00:02 »
Quote
author=Bored chemist link=topic=7454.msg80123#msg80123 date=1177523686]
Not all balls are full of air.
My one is.:)

Quote
BTW, how many bounces does it take before the ball actually stops?
Would depend on how rigid the surface of my ball full of air was.
 

Offline Batroost

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« Reply #11 on: 25/04/2007 19:28:58 »
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The internal molecular vibrations that correspond to heat are much faster than the "bounce".

Nope. I'm thinking of the compression/relaxation of a solid (or near-solid) rubber ball. Work is being done on the substance of the ball by this process (i.e. force x distance) and, as it will be less than 100% efficient, there will always be some loss of energy as heating of the ball. I think the slower the compression/relaxation the more efficient the process may be?
 

Offline DoctorBeaver

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Bouncing a ball on the moon.
« Reply #12 on: 26/04/2007 08:43:50 »
As most of the moon's surface is covered in thick dust the ball probably wouldn't bounce at all  :D
 

Offline lightarrow

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Bouncing a ball on the moon.
« Reply #13 on: 26/04/2007 17:38:44 »
Quote
There would be a greater number of bounces, actually, because of no air...
Imagine you tried the expermient inside a sealed (fully evacuated) container on the earth. This negates any effect of air pressure. The ball will still stop bouncing because it is not having perfectly elastic collisions with the ground i.e. some of the work done in compressing the ball is lost as heat.
But, the collisions between the ball and the surface on the moon are slower. Might this mean that they are more elastic, with less heat generated/energy lost (a bit of a guess this)? In which case the ball would complete more bounces before coming to rest on the moon than on the earth.
Yes, I think it's correct. There would be more bounces also because of less anelastic heat dissipation (in the air inside the ball and in the elastic envelope).
« Last Edit: 26/04/2007 17:40:20 by lightarrow »
 

Offline Bored chemist

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Bouncing a ball on the moon.
« Reply #14 on: 26/04/2007 18:57:35 »
"Nope. I'm thinking of the compression/relaxation of a solid (or near-solid) rubber ball. Work is being done on the substance of the ball by this process (i.e. force x distance) and, as it will be less than 100% efficient, there will always be some loss of energy as heating of the ball. I think the slower the compression/relaxation the more efficient the process may be?"

I'm also thinking about the ball bouncing and the energy being converted to heat. I think that the bouncing of the bal is always very slow compared to the processes by which the kinetic / elastic energy of the ball is converted to heat.
 

Offline Batroost

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Bouncing a ball on the moon.
« Reply #15 on: 26/04/2007 20:04:30 »
OK, sorry mis-understood your point.

I seem to remember from thermodynamics that this sort of thing was less 'lossy' when slower - but that was a long time ago.... Anyone been taught thermodynamics recently or a materials scientist perhaps?
 

Offline ukmicky

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Bouncing a ball on the moon.
« Reply #16 on: 26/04/2007 22:10:23 »
As most of the moon's surface is covered in thick dust the ball probably wouldn't bounce at all  :D
Good point :)
 

lyner

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Bouncing a ball on the moon.
« Reply #17 on: 27/04/2007 19:38:19 »
With a simple model - a solid ball, the energy lost on each impact would be the same proportion in the Moon and on Earth. There would be more bounces on the Moon because there would be no energy loss due to air resistance.
Because the frequency of the bounces would be lower on the moon (for a given dropping height) the answer would be  a longer actual time for bouncing but the same number of bounces,  if you did the experiment in a vacuum on Earth and eliminated air resistance.
 

Offline Batroost

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Bouncing a ball on the moon.
« Reply #18 on: 27/04/2007 19:55:31 »
Quote
With a simple model

And where's the FUN in that ?!? (LOL)
 

lyner

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Bouncing a ball on the moon.
« Reply #19 on: 27/04/2007 19:59:32 »
Point taken.  But doing it in a vacuum could be breathtaking.
 

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Bouncing a ball on the moon.
« Reply #19 on: 27/04/2007 19:59:32 »

 

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