Everything Science Grade 11

12.2 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE

• The force of the car pulling on A (towards the right)


• The force of B pullingon A (towards the left)


• The force of the Earth pulling downwards on the trailer (gravity)


• The force of the road pushing upwards on the trailer


• The force of friction between the wheels of A and the road (opposite tothe direction of motion)

Force Diagrams ESBET

If we look at the example above and draw a forcediagram of all the forcesacting on the two-trailer-unit,
the diagram would looklike this:

Ff: Frictional force F 1 : Force of car on trailers (to the right)

FN: Upward force of road ontrailers

Fg: Downward force of Earth on trailers

on trailers (to the left)

It is important to keep the following in mind when you draw force diagrams:

• Make your drawing large and clear.


• You must use arrows and the direction of the arrow will show the direction of the force.


• The length of the arrowwill indicate the size ofthe force, in other words, the longer arrows in
  the diagram (F 1 for example) indicates abigger force than a shorter arrow (Ff). Arrows of the
  same length indicate forces of equal size (FNand Fg). Use “little lines” likein maths to show
  this.


• Draw neat lines usinga ruler. The arrows must touch the system or object.


• All arrows must have labels. Use letters with akey on the side if you donot have enough space
  on your drawing.


• The labels must indicate what is applying theforce (the force of the car?) on what the force is
  applied (?on the trailer?)and in which direction (to the right)


• If the values of the forces are known, these values can be added to the diagram or key.