Describing Forces

Force diagrams are a way of describing and representing forces. A force is described by its:

  • magnitude, i.e. the size of the force
  • direction
  • location, i.e. where the force is applied.

Measurement of Force

The Newton (N) is the standard unit used for measuring a force. One Newton (N) is the amount of force required to support 100g.


A force may be represented as a line. The length of the line is drawn to any convenient scale, e.g. 1N = 1mm, so 100N = 100mm, etc.

The direction of the force is indicated by an arrowhead on the end of the line.


The Resultant of Two Inclined Forces

To find the resultant of two inclined forces, we can draw a vector diagram called the parallelogram of forces. In the example below, the resultant is found by drawing a line parallel to "ao" and to "ob" to make a parallelogram as shown. The resultant is found by drawing a line "oc" and measuring its length.

Parallelogram of forces

Equilibrium of Three Forces

Link to Triangle of Forces animation
Click on the screenshot above to view the "Triangle of Forces" animation by Laszlo Lipot


An image showing the Flash animation logo SWF Flash logo is a link to a Flash animation.

Flash animations are embedded into the pages of all my D&T Modules but there are pictorial links to the animations on this web site so that devices that cannot play Flash animations will at least show a jpeg screenshot of the animation.

If your PC or personal digital assistant (PDA) can play Flash animations you may click on an image showing the Flash animation logo SWF Flash logo to view the animation in a new window.
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Copyright Laszlo Lipot.