Edexcel International A Level Maths: Mechanics 1

Revision Notes

1.1.4 Types of Force

Test Yourself

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

1.1.4 Types of Force Diagram 1_1, downloadable Edexcel A Level Mechanics revision notes

1.1.4 Types of Force Diagram 1_2, downloadable Edexcel A Level Mechanics revision notes

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.

1.1.4 Types of Forces Question Image, downloadable Edexcel A Level Mechanics revision notes

1.1.4 Types of Forces Question Solution, downloadable Edexcel A Level Mechanics revision notes

Exam Tip

  • 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

  • You should always round your answers to three significant figures, however if using g = 9.8 m s-2 within a calculation, use two significant figures.

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