# Investigation of the laws of equilibrium for a set of co-planar forces

In this experiment a metre stick is suspended from two newton balances and four masses are hung from the stick. The masses are changed or moved around until the stick is level. The two conditions for equilibrium should then hold:
(i) the total force up = total force down
(ii) for any point on (or off) the metre stick the sum of the clockwise moments = the sum of the anticlockwise moments.
Note: Masses can be changed using the M+ and M- buttons and can be moved with the sliders. The weight of the metre stick, at the 50 cm mark, is 1 N and each hanging mass is 20 g. A small spirit level (assumed weightless) sitting on the stick indicates when it is level (remember the bubble always goes to the high side).

Procedure:
1. The sliders allow you to move the masses. The M+ and M- buttons allow you to change the masses.

2. Change and move the masses until you get the system in equilibrium (the bubble in the middle)

3. Into your copy draw the forces acting on the stick (don't forget the weight of the stick) and the position of each of the forces.

4. Pick any point on the stick and calculate the sum of the clockwise moments and the sum of the anticlockwise moments about that point.

Analysis:
It is easiest to calculate moments about the zero mark of the metre stick. Convert the masses to weights and don't forget the weight of the stick.

Precautions:

• Check that the centre of gravity is at the 50 cm mark on the metre stick
• Ensure that the Newton balances are vertical and the metre stick is horizontal when readings are taken.

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