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).
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.