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Chapter 9
Momentum and Its
Conservation
9.1 Impulse and Momentum
Newton called momentum “the quantity of
motion.”
- He wrote his three laws in terms of
momentum.
How is velocity affected by force?
- Newton’s second law
Relating impulse to momentum
F = ma = m ∆v/∆t
F∆ t = m ∆v
Using the impulse – momentum theorem
F∆ t = p2 – p1
where p2 = mv2
and p1 = mv1
9.2 Conservation of Momentum
Two particle collision
Because the time intervals are the same
for the collision of the two particles, the
momenta must be the same
momenta before = momenta after
Momentum in a closed system
A system that does not gain or lose mass
is said to be a closed system. Also, all
forces affecting the system are internal
forces. The net external force on a closed
system is zero and the system is called an
isolated system.
Conservation of Momentum law
The momentum of any closed
isolated system with no external
force does not change.
Explosions
Just like a collision only backwards.
Two-dimensional collisions
The law of conservation of momentum
holds true regardless of the directions of
the objects before and after collision.
Remember, momentum p, is a vector and all
the vector rules apply.