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Offline ukmicky

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bounce
« on: 18/06/2006 17:02:53 »
Yesterday i was in my garden enjoying the summer sun and drinking large amounts of alcohol. After i finished one bottle of lager i threw the empty glass bottle across the lawn towards the bin but misjudged my throw causing the bottle to hit a concrete paving slab , but to my amazement it didnt smash it just bounced and it got me wondering how does something bounce.

if the two items which come together are made out of hard substances preventing compression of either like glass and concrete where does the upward spring come from.

Michael


 

Offline Roy P

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Re: bounce
« Reply #1 on: 18/06/2006 17:37:21 »
quote:
Originally posted by ukmicky
if the two items which come together are made out of hard substances preventing compression

'Appears' to prevent compression. There's your answer, Mike me-old-matey! Watch two heavy steel balls bounce of each other. Even diamonds 'compress' -- don't they?! The harder the substance, the stronger the 'bounce'.

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Offline ukmicky

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Re: bounce
« Reply #2 on: 18/06/2006 17:49:54 »
Hmmm :) why doesnt something hard just hit the floor and slide or break,   how does downward movement change to upward spring.

Michael
 

another_someone

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Re: bounce
« Reply #3 on: 18/06/2006 19:50:55 »
My own, totally unscientific, observation is that when something hard bounces it tends to be caused by spin of some kind.  When you through the bottle, you imparted a horizontal force in the line of flight, as well al the vertical force given it by gravity.

As a comparison, I would look at the way a parachutist, when hitting the ground, will use roll to absorb the impact with the ground.



George
 

Offline Solvay_1927

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Re: bounce
« Reply #4 on: 19/06/2006 01:29:49 »
A couple of thoughts:

1.  Newton’s 2nd law – when a moving object hits a stationary object, the stationary one imparts back TO the moving one the same force as it receives FROM the moving one.

If the moving object is soft (compressible, inelastic) then the force it receives back will generally lead to deformation (i.e. it goes ‘splat’).

If the moving object is of similar hardness to the stationary one, then the force it receives back is likely to lead either to “shearing” (i.e. it goes “smash”) or to it being repulsed backwards with (much/most of) the same speed that it came in at (i.e. it bounces back – the “upward spring”).

2.  Whether the bottle breaks or bounces depends not only on how much force it receives (how fast it's moving / how heavy it is), but also on how the force it receives back from the concrete disperses through the glass.

If the forces do not “spread out” evenly (because of angle of trajectory, shape of the bottle, imperfections in the glass, etc.) then you’ll get places in the glass where one force is moving in one direction and immediately adjacent to it another force is moving in a contrary direction – leading to a “shearing” action, and hence breakage.

It might be useful to think of an egg shell.  If you place the shell on its side and stand on it, it breaks. But if you place the shell upright and step very carefully on to it, you can avoid breakage.  That’s because of the way the shell dissipates the force applied to it when you stand on it – pointy end up, the force is transmitted to the ground without any “shearing” forces arising.

For the same reason, a thin-walled test tube dropped on a hard surface will normally smash, but it could bounce if it lands on its rounded end (because the shape of the rounded end dissipates the force more effectively).

Well, that’s my understanding anyway.  But I could be wrong.
 

Offline neilep

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Re: bounce
« Reply #5 on: 20/06/2006 21:57:54 »
quote:
Originally posted by ukmicky

Yesterday i was in my garden enjoying the summer sun and drinking large amounts of alcohol. After i finished one bottle of lager i threw the empty glass bottle across the lawn towards the bin but misjudged my throw causing the bottle to hit a concrete paving slab , but to my amazement it didnt smash it just bounced and it got me wondering how does something bounce.

if the two items which come together are made out of hard substances preventing compression of either like glass and concrete where does the upward spring come from.

Michael



Mikey baby....I am sure the bottle did smash.....you're just still too frazzled to notice...or even care !:)...

....else...you have a concrete slab with schizophrenic tendencies and at that precise moment it had a Jekyll-Hyde moment and thought it was a slab of Jelly...............Yes.. I am sure that's it !



Men are the same as women, just inside out !
 

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Re: bounce
« Reply #5 on: 20/06/2006 21:57:54 »

 

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