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?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

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.