Momentum Notes

Momentum Momentum ( ρ) – inertia in motion Mass x Velocity ρ = mv measured in kg·m/s

When doing calculations…

Impulses Product of the average net force exerted on an object and the time interval over which the force acts. F t = impulse (J) Impulses are measured in Ns

Impulse/Momentum Theorem Impulse of an object is equal to the change in momentum it causes F t = mv 2 – mv 1

Law of Conservation of Momentum Law of conservation of momentum says that in the absence of an external force, the total momentum of a system remains unchanged.

Law of Conservation of Momentum – Continued 1) This law applies to a closed system (one where no mass is gained or lost)

Law of Conservation of Momentum – Continued Momentum conserved if: 2) At all times, only two objects are involved 3) The only forces involved are internal

Types of Collisions Elastic Collisions – when objects collide without being permanently deformed and without generating heat Ex: Billiard balls colliding

Types of Collisions Inelastic Collisions – whenever colliding objects become tangled or couple together Ex: Two freight train cars hitting and continuing

Calculations momentum before collision = momentum after collision ρ before = ρ after ρ 1 + ρ 2 = ρ 1 + ρ 2

Calculations - continued m 1 v 1 + m 2 v 2 = m 1 v 1 + m 2 v 2 (used in elastic collisions) m 1 v 1 + m 2 v 2 = m total v total (used in inelastic collisions)

Example: