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Physics 8463 - 4.5 Forces

4.5.7 Momentum

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4.5.7.1 Momentum

Momentum is a property of moving objects.

Momentum is defined by the equation:

momentum = mass × velocity
p = mv

This equation is NOT given on the Physics equation sheet - you need to know it, what the letters mean and are measured in!

p = momentum, in kilograms metre per second, kg m/s

m = mass, in kilograms, kg

v = velocity, in metres per second, m/s

  
4.5.7.2 Conservation of momentum

In a closed system, the total momentum before an event is equal to the total momentum after the event.

This is called conservation of momentum.

You should be able to use the concept of momentum as a model to:

describe and explain examples of momentum in an event, such as a collision

complete calculations involving an event, such as the collision of two objects.

  
4.5.7.3 Changes in momentum

When a force acts on an object that is moving, or able to move, a change in momentum occurs.

The equations F = ma and a = v − ut combine to give the equation

F = mΔv/Δt

F= Δp/Δt

This equation is given on the Physics equation sheet - but you need to know what the letters mean and are measured in.

where mΔv = change in momentum

and mΔv/Δt = rate of change in momentum

so, force equals the rate of change of momentum.

You should be able to explain safety features such as: air bags, seat belts, gymnasium crash mats, cycle helmets and cushioned surfaces for playgrounds with reference to the concept of rate of change of momentum.

You should be able to apply equations relating force, mass, velocity and acceleration to explain how the changes involved are inter-related.

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