Momentum & its conservation

Fc Ft

Fc = mc change in vc time

Fc time = mc change in vc

Ft = mt change in vt time

Ft time = mt change in vt

Fc time + Ft time = mc change in vc + mt change in vt

(Fc + Ft)time =change in mcvc + change in mtvt

Car truck collision

(Fc + Ft)time =change in (mcvc + mtvt)

Fc Ft

Car truck collision

(Fc + Ft)time =change in (mcvc + mtvt)

Newton’s 3rd law: Fc = -Ft (Fc + Ft)time = 0

0 = change in (mcvc + mtvt)

mcvc + mtvt stays constant!

Momentum = mvmcvc = momentum of car

Mtvt= momentum of thruck

mcvc + mtvt = total momentum

this changesthis changes

this stays constant

Momentum is conserved!

Before = -40

After = -40

True for all collisions

before =+20

after =+20

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Revisit the canoe at the dockInitial momentumcanoe = 0boy = 0Total = 0

final momentumcanoe = mcvcboy = mbvbTotal = 0

Momentum is a vector: mvcollision in 2 dimensions

Finding nemoeating

Billiard balls

2before

1ptot 1

2

afterptot

Conservation of momentumon a sub-atomic level

- meson- meson

proton

p

p

before

after

ptot

ptot

Rocket travel

before

P0

after

P0 + pexhaust

p

Rifle recoil

mVmV

Machine-gun granny