# Impulse, Momentum and Conservation of Momentum

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16-Jan-2016Category

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### Transcript of Impulse, Momentum and Conservation of Momentum

Impulse, Momentum and Conservation of Momentum

Newton Again!Newton observed objects colliding and realized that two things dictate what it takes to change the motion of an object.Mass (how much matter)Velocity (how fast its going in a given direction)

He Called This Momentump = m.v

ImpulseBy rewriting his own 2nd law, Newton defined Impulse F=m.a=m. F.t=m.v = IMPULSE JJ=F.t= m.v=p=change in momentum

If a 5 N force pushes a 2 kg object for 3 seconds, how much will the momentum change? How much is the impulse? How much will the speed change?

How much is the acceleration?

Conservation of MomentumLets look at what happens to momentum before, during and after a collision/explosion.

If pGun/Emily = pPotato ThenMgun/Emily.vgun/Emily=mpotatoe.vpotatoIf the mass on the left of the equation is large compared to the right, then the velocity on the right must be large compared to the left if they are to be equal.

Action/ReactionConservation of momentum is just a consequence of Newtons third Law

Conservation of MomentumLets look at what happens to momentum before, during and after a collision/explosion.

Momentum is Conserved TZ student defends school with potato gun

Conservation of MomentumNewtons Third Law:The potato goes one way and the gun recoils in the opposite direction.The gun exerts a force on the potato and the potato exerts an equal but opposite force on the gun, recoil.

pGun/Girl = pPotatoThese forces produce equal but opposite changes in momentum.Since the girl is attached to the gun, the combination of the girl /gun mass is much greater than the mass of the potato.The girl and the gun recoil at a velocity much smaller than the potato.

If pGun&Person = pPotato ThenMgun/person.vgun/person=mpotatoe.vpotatoIf the mass on the left of the equation is large compared to the right, then the velocity on the right must be large compared to the left if they are to be equal.

Before collisionAfter collisionThe system has the same total momentum. M=2000 kg, v = 5 m/sM = 500 kg, v = 0

Impulse JBy rewriting his own 2nd law, Newton defined impulse F= m . a =m . F . t = m . vJ = F . t= mv = p =change in momentum

So the safest way to stop an object is to stretch out the time it takes to stop things so you could use the smallest possible force. Thats why if something is cushioned and soft it is less likely to break.

Action/ReactionConservation of momentum is just a consequence of Newtons third Law