Why do we need 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

What types of forces could be involved?

• ?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?(RN)

• 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
    • If you are told, or are using?g =?9.8 m s-2??ensure you?round?your?final?answer?to?two?significant?figures?(as 9.8 is rounded to 2 s. f.)
    • If you are told to use g =?10 m s-2?ensure you?round?your?final?answer?to?one?significant?figure?(as 10 is rounded to 1 s. f.)
  • friction?acts?parallel?to the surface in the?opposite?direction to?motion
  • the?normal?reaction?acts?perpendicular?to the surface (and?friction)