Momentum

Momentum is the tendency of an object to continue to move as it was.

In the imperial system it was known as 'inertia'. In everyday language we often talk of the momentum of a moving object keeping it going and 'overcoming the inertia' in order to get a stationary object to move. In reality they are exactly the same principle.

Momentum is a vector which means it has both direction and magnitude. This is because it is calculated using an object's rather than its speed.

The greater the mass of a moving object, the it is to stop: so the its momentum. Momentum is proportional to mass.

The greater the speed of a moving object, the it is to stop: so the its momentum. Momentum is proportional to speed.

Therefore momentum is calculated by multiplying an objects mass by its velocity:

p = m × v
	where	p	=	Momentum
		m	=	Mass in , ()
		v	=	Velocity in , ()

This can be summarised in the following 'magic triangle':

Although the symbol for momentum is 'p', it is common to use 'mv' in diagrams and calculations instead.

The units of momentum do not have their own symbol or name, instead they are a combination of the units of mass and velocity multiplied, ie:

kg m/s (or kg ms^-1)

1. Calculate the momentum of a rugby player, mass 120 kg moving at 3 m/s.

2. Calculate the mass of a car that when moving at 25 m/s has a momentum of 20 000 kg m/s.

3. Complete the following table:

   (kg m/s)	(kg)	(m/s)
   	50	3
   160		20
   1500	250
   	200 g	20
   3		50 cm/s