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Mechanics

Aim: to show that Forces can be added in the same way as Displacements
Displacements can be added by drawing a scale diagram (either a triangle or a parallelogram).
The aim of this experiment is to see if forces can be added using the same method.
If forces can be added in the same way as displacements, we are probably justified in assuming that all vector quantities can be added this way.

Method
Hold (or fix) three spring balances (also called dynamometers) as shown in the diagram below.
If the point O is stationary, then the three forces are in equilibrium.
This means that force A is balancing the combined effects of forces B and C.
Similarly, force B balances the combined effects of forces A and C (and force C balances the combined effects of forces A and B).

 1. Accurately mark on the paper the positions of points O, A, B and C. Write beside A, B and C the magnitudes of the forces (readings of the spring balances). 2. Draw lines joining O to A, O to B and O to C, so that your diagram records the directions in which the forces were acting as well as the magnitudes of the three forces. 3. Repeat the procedure with forces of different magnitudes pulling along different directions.

Analysis of the results
Using a suitable scale, add arrows to the diagram representing the three forces.
For example, if your scale is: 1cm represents 0.1Newtons, a force of magnitude 0.8N would be represented by an arrow 8cm long.

On the diagram, do the vector addition FA + FB as shown in the example below.

Is the result of this addition equal but opposite to the force FC ?

Note that each set of results allows you to attempt to verify the principle three times.

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