Law of conservation of momentum in a non isolated system.

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  • Thread starter Ali Hamaiz
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  • #1
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Is the law of conservation of momentum valid in non isolated system . What is an isolated system? My teacher confuses me that the law is valid in an non isolated system . They even say that when we say about the isolated system (meaning they are present ) we do not consider the air resistance or frictional forces is that true? They give me the example of a gun recoiling , I am confused .
 

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  • #2
BvU
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Isolated in this case means no external forces and no mass crossing the boundary. A tennis ball in the air is not an isolated system: it will fall to the ground. A gun also, but if you look in the direction of where it's aiming then the momentum in that direction is conserved.
 
  • #3
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@BvU what are you talking about the direction?
 
  • #4
BvU
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You need a constant force to keep the gun from dropping to the floor. But to calculate the kickback you can use conservation of momentum in the direction the bullet flies.
 
  • #5
jbriggs444
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You need a constant force to keep the gun from dropping to the floor. But to calculate the kickback you can use conservation of momentum in the direction the bullet flies.
[and make sure that you place the boundaries around the "system" so that both gun and bullet remain inside]
 
  • #6
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What will be the conclusion , will the law of conservation of momentum hold in an non isolated system .
 
  • #7
BvU
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No. See #2.
 

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