Impulse, Momentum and Conservation of Momentum
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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 it’s going
in a given direction)
He Called This Momentum
p = m.v
Impulse By rewriting his own 2nd law, Newton
defined Impulse
F=m.a=m.
F.t=m.Δv = IMPULSE “J” J=F.t= m.Δv=Δp=change in momentum
t
v
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 Momentum
Let’s look at what happens to momentum before, during and
after a collision/explosion.
If pGun/Emily = pPotato Then
Mgun/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/Reaction
Conservation of momentum is just a
consequence of Newton’s third Law
Conservation of Momentum
Let’s 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 Momentum
Newton’s 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 Then
Mgun/person.vgun/person=mpotatoe.vpotato If 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 collision
After collision
The system has the same total momentum.
M=2000 kg, v = 5 m/s M = 500 kg, v = 0
Impulse “J”By rewriting his own 2nd law, Newton defined
impulse
F= m . a =m .
F . t = m . ΔvJ = F . t= mΔv = Δp =change in momentum
t
v
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. That’s why if something is cushioned and soft it is less likely to break.
Action/Reaction
Conservation of momentum is just a
consequence of Newton’s third Law