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Mechanics

Cool goIITian

 Joined: 11 Aug 2009 Post: 38
5 Oct 2009 18:55:17 IST
0 People liked this
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why is it that if we fire a bullet towards a glass pane it doesnt break but instead if we throw a st
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why is it that if we fire a bullet towards a glass pane it doesnt break but instead if we throw a stone it breaks?

Blazing goIITian

Joined: 29 Oct 2008
Posts: 536
5 Oct 2009 20:43:41 IST
1 people liked this

the speed of bullet is very large so it comes in contact with glass for fractions of seconds..which is not sufficient to impart momentum to the nearby particles and thus their inertia dominates..resulting into a clear cut hole (size of bullet)..in case of stones its just opposite

Forum Expert
Joined: 5 Oct 2009
Posts: 125
5 Oct 2009 20:51:19 IST
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I do not think this is true. REMEMBER that whatever we talk about Newtonian mechanics is under certain assumptions. Here, we can't assume that the glass is a rigid body. It is GLASS which will have certain properties which a rigid wall does not have.

Talk about these properties and you will realize that it is teh case everywhere. If a bullet hits a glass and it doesn't crack - it is a bulletproof glass. If a stone is thrown at glass and it breaks - it is glass, but not bulletproof. Realize this!

I'd be really pleased if you could carry on a discussion on this rather than just stop here!

Cool goIITian

Joined: 11 Aug 2009
Posts: 38
5 Oct 2009 20:59:25 IST
1 people liked this

i mean to say the glass does make a hole but why is it smaller wen compared to stone?

Hot goIITian

Joined: 25 Sep 2009
Posts: 178
5 Oct 2009 21:38:13 IST
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i think i approve to rahul kumars answer.perfect

Hot goIITian

Joined: 20 Apr 2008
Posts: 195
5 Oct 2009 21:53:23 IST
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In case of bullet , the shear stress created is sufficient to rip off the glass due to high impulse acting on a small area which is primarily due to high velocity of bullet.

In case of stone the velocity is low and size is large compared to bullet. So it fails to develop sufficient shear stress to punch the glass. So entire impulse causes bending of the glass which causes a tensile stress on the body. Glass is very weak in tension and it breaks along the radial lines due to this .

New kid on the Block

Joined: 12 Jul 2012
Posts: 1
12 Jul 2012 17:14:03 IST
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why is it that if we fire a bullet towards a glass pane it doesnt break but instead if we throw a stone with same velocity it breaks the glass.....

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