Momentum and Impulse

Momentum definition

the product of an object's mass and its velocity (equation is p = m.v)

unit for momentum

kg.m/s or N.s

Momentum as a vector quantity

Momentum is a vector quantity because velocity is but mass is not. Thus you need to state a direction and take it into account in all calculations

When a resultant force is applied to a body what happens?

It accelerates. This means that its velocity and hence its momentum change. The change in velocity depends on both the mass of the body and the size of the resultant force applied.

Newtons second law re-written

The net (or resultant) force acting on an object is equal to the rate of change of momentum of the object in the direction of the net force.

Impulse definition

The product of the resultant/net force acting on an object and the time the net force acts on the object.

The change in momentum of a particular mass depends on (2)

- the size of the resultant force

- the length of time it is applied

Principle of conservation of linear momentum

The total linear momentum of an isolated system remains constant (is conserved) (pfinal = pinitial)

Isolated

means that no external forces are acting on the system

Kinetic energy is only conserved when...

the collision is perfectly elastic (Ek = 1/2m.v^2)

Elastic collisions

both momentum and kinetic energy are conserved

inelastic collision

Momentum is conserved but kinetic energy is not — energy is lost as heat, sound, or deformation.

What is a perfectly inelastic collision?

Objects stick together. [m₁vi₁ + m₂vi₂ = (m₁ + m₂)vf.] [Momentum conserved; EK not conserved.]