Force Diagrams

Force diagrams are used to help understand a given scenario and show which forces are acting on which particles and in which direction they are acting
In diagrams an arrow is used to represent a force acting on a particle which shows the direction in which the force is acting
The magnitude of the force is normally written next to its arrow

3-1-1-fig1-basic-force-diagrams

Specific types of force encountered (which may not be mentioned in the question nor labelled on a given diagram) are: weight (W N), tension (T N), thrust (T N), friction (F N) and
normal reaction (R N)

Remember that the diagram is drawn to help understand the scenario - cars, blocks, etc are modelled as particles occupying a single point in space and so all forces acting on the car, block, etc act at that same single point
The main forces that you will see are:
- tension (a “pulling” force) acts away from a particle,
  thrust (a “pushing” force) acts towards it
- weight is W = mg where m kg is the mass of the particle and g is the
  acceleration due to gravity – usually g = 9.8 m s^-2
- friction acts parallel to the surface in the opposite direction to motion
- the normal reaction acts perpendicular to the surface (and friction)

3.1.1_WE_Force_1

3-1-1-fig3-we-solution

Always draw a force diagram if appropriate.
If a diagram is already given then add to it as you progress through the question.
If a diagram is too small or it gets too complicated then draw a new diagram.
You may be able to manage with just drawing the section of the diagram you are dealing with in any particular question part.

Force Diagrams (Edexcel International AS Maths: Mechanics 1)