Chapter 7 – Momentum
also
Intro to Rotational Motion
Today
:
Hand in Homework #3
Pickup Homework Assignment #4
Pickup graded homework and quizzes
Today’s Topics
:
Finish Chap 7
Momentum and Impulse
Momentum Conservation
Intro to Chap 8
Rotational Inertia

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Conservation of Momentum
Newton’s 2
nd
& 3
rd
Laws
F = ma = dp/dt
“If the net external force acting on a system is zero,
the total momentum is conserved.”
examples:
Flying projectile explodes
–
fireworks (except for gravity)
–
multiple warhead missile, rocket propulsion
initially
afterwards
If
no external forces
, traveling at v = constant,
Call the forces between the pieces of the projectile internal forces
.
by Newton’s 3
rd
Law:
internal forces act in equal and opposite pairs
These internal forces balance to zero
(Before and After explosion)
Internal forces produce no net change in momentum!
Explosions conserve momentum
“pow”