Types of Force (AQA A Level Maths) : Revision Note
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Types of Force
What is a force?
A force is a vector quantity, it has both magnitude and direction
A force is a push or a pull on an object
A force is measured in Newtons
In A level mathematical models, forces act at a single point called a particle which occupies a single point in space
What types of force are used in mechanics?
Weight is the effect of mass and gravity, it always acts downwards
Tension is a pulling force, it always acts away from an object
Thrust is a pushing force, it always acts towards an object
Friction is a resistive force, it acts to oppose the motion of an object
Every surface will produce a reaction force, it will always act perpendicular to the surface
Mass, Gravity and Weight
Mass is a measure of the amount of matter in an object
Mass is a scalar quantity, measured in kilograms, kg
Mass is universal, it does not change based on location
Gravity is the force by which a body (usually a planet or a star) pulls objects towards its centre
g is the acceleration due to gravity, measured in m s-2
On Earth, g is approximately 9.8 m s-2 , although its exact value varies with location
g is different elsewhere in the universe
Weight is the product of mass and gravity, it is a force measured in Newtons
Weight is a vector quantity
Weight varies with location
Weight always acts vertically downwards towards the ground
Worked Example
The diagram below shows a car towing a trailer by a light inextensible string.
Forces D, R, F and T N act on the car and caravan as shown.
Write a brief description of which each force represents.
Examiner Tips and Tricks
There are many phrases/words that can be used implying the types of force
Braking – suggests thrust
Air resistance – suggests a resistive force
Always sketch a diagram and mark the forces on the diagram clearly
It will help you understand the problem
Add more things to the diagram as you progress through the question
You may not even need all the forces from your diagram
The value used for g in questions tells you how you should round any answers
If g = 9.8 m s-2, use two significant figures
If g = 10 m s-2, use one significant figure
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