Types of Force (Edexcel IAL Maths)

Spec point — 4.1

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.

Answer:

Exam Hint

• 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.