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9 Jul 2009 22:50:24 IST

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Newton's 1st law states " EVERY BODY continues in its state of rest or of uniform motion in a straig

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Newton's 1st law states " EVERY BODY continues in its state of rest or of uniform motion in a straight line unless it is compelled by ext. force to change dat state. "suppose a time bomb is placed somewhere. It is at rest and we conclude dat it will continue to remain so. But after some time , the bomb explodes & da splinters run here and there. Obviously the body ( i,e da bomb or whatever remains of it ) can no longer said to be at rest as it was some time ago. And no EXTERNAL FORCE was put.

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ramyani chakrabarty

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9 Jul 2009 22:51:18 IST

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Is it a breakdown of 1st law ?

NugoRama

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9 Jul 2009 22:58:47 IST

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the centre of mass was at rest ..remains at rest after exploding too.

no law violated !!

dc16

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9 Jul 2009 22:58:49 IST

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actually it can be explained by the concept of momentum.... as initially the net linear momentum of the BOMB was zero... and after explosion the net momentum of all it's particles will remain zero as no external force acts on it..!!

dc16

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9 Jul 2009 23:00:51 IST

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yeah.. PERFECT nugo..!

ramyani chakrabarty

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9 Jul 2009 23:57:10 IST

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But da concept of COM motion involves da 3rd law of newton & also da constancy of mass.

NugoRama

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10 Jul 2009 00:08:41 IST

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" But da concept of COM motion involves da 3rd law of newton & also da constancy of mass."

Dunno what this means ..but there was no external force on the bomb ..hence its COM remained at rest.

COM is related with all the laws of motions ...is the bomb thing clear ?

Siddharth Kothari

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10 Jul 2009 00:14:26 IST

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I guess, here the question is why the body moves (i.e. splinters) when the bomb explodes and not about the c.o.m being at rest.

If so, initially, chemical energy was stored in the bomb; which when the bomb exploded, converted into kinetic energy & may be heat energy.

Thus, energy is conserved.

Otherwise, the answer is clear from earlier posts.

NugoRama

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10 Jul 2009 00:17:49 IST

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Yes ofcourse ..the energry required is coming from chemical evergy .

I thot the question was that if it violates the first law or not.

ramyani chakrabarty

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10 Jul 2009 00:26:37 IST

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yes.

the question is why the body moves (i.e. splinters) when the bomb explodes and not about the c.o.m being at rest.

But da expln is not clear.

R we to define 2 types of bodies ----where chemical energy is stored and where not ?

NugoRama

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10 Jul 2009 00:30:30 IST

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Its not always the chemical energy ..

ramyani chakrabarty

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10 Jul 2009 00:58:25 IST

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so is da 1st law valid for only some types of bodies ?

NugoRama

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10 Jul 2009 01:03:21 IST

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First law ( and others too..) is applicable for point sized bodies ..and when we talk of Bigger bodies ..we take the COM into concern ..hence no law is violated ..Plus ..the reason that the parts of the bomb come into motion is that they gain mechanical energy due to the loss ofd chemical energy.

ramyani chakrabarty

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10 Jul 2009 01:15:00 IST

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" First law ( and others too..) is applicable for point sized bodies "

but a chair at rest will always be at rest unless some ext force is applied.

Chair is not point sizes.

NugoRama

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10 Jul 2009 01:15:50 IST

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The centre of mass of chair will be at rest ...not the whole chair.

Consider a couple of torque as an example here.

ramyani chakrabarty

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10 Jul 2009 01:18:30 IST

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...not the whole chair.??

which part shall start moving if no ext force is applied ?

NugoRama

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10 Jul 2009 01:19:46 IST

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Didnt i just said "couple of torque" ?

Take a frictionless surface .Put achair on it .and apply a COUPLE OF TORQUE. It will rotate about the com ..Get it ?

ramyani chakrabarty

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10 Jul 2009 01:22:14 IST

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no force , no torque is applied.

" EVERY BODY continues in its state of rest or of uniform motion in a straight line unless it is compelled by ext. force to change dat state. "

NugoRama

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10 Jul 2009 01:24:02 IST

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" EVERY BODY continues in its state of rest or of uniform motion in a straight line unless it is compelled by NET ext. force to change dat state. "

U forgot the word NET there ..

a couple of torque = No net force.

NugoRama

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10 Jul 2009 01:27:28 IST

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And incase goiit gets into maintenance all of a sudden ..heres my id nugorama@gmail.com ..i wont sleep tonite ..and if u'll allow me ..i wont let u too.

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