Force Diagrams

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.

Vectors

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.

Equilibrium of Three Forces

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

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