Newtons Laws of Motion and Momentum

Newtons first law states that

an object will remain at rest or keep traveling at constant velocity unless it is acted upon by an external resultant force

Newtons second law states

The net force acting on an object is equal to the rate of change of momentum. The net force and change in momentum are in the same direction.

Newtons third law states

When two bodies interact, the forces that they exert on each other are equal in magnitude and opposite in direction

The net force acting on a body =

rate of change of momentum

If mass remains constant Newton’s second law becomes

Force = m(Δv/Δt) = ma

Impulse is defined as

Average force acting on body × the time for which it acts

Impulse and momentum are linked by

Impulse = change in momentum

The are under a force - time graph =

Impulse

Linear momentum is defined as

mass × velocity

The unit of momentum is

kgms^-1

Principle of conservation of momentum

In a closed system, the total momentum remains constant.

A ‘closed system’ is

When no external forces act

In an elastic collision the quantities conserved are

momentum, kinetic energy and total energy

In an inelastic collision the quantities conserved are

momentum and total energy NOT kinetic energy

The unit of impulse are

Ns