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Principle of moments

The principle of moments states that when a body is in equilibrium, the sum of clockwise moments about the pivot is equal to the sum of the anti-clockwise moments about the same pivot.

When the clockwise moments do not equal the anti-clockwise moments there is a resultant moment.

A weight of $$160 \text{ N}$$ is placed $$0.3 \um$$ to the left of the pivot. This causes an anti-clockwise moment of $$160\text{ N} \times 0.3 \text{ m} = 48 \text{ Nm}.$$

A second weight of $$240 \text{ N}$$ is added to bring the system to equilibrium. The weight needs to be placed so that it causes a clockwise moment of $$48 \text{ Nm}.$$

The distance between the second weight and the pivot must be equal to $$\displaystyle \frac{48\text{ Nm}}{240 \text{ N}} = 0.2 \text{ m}.$$

The clockwise moments equal the anti-clockwise moments. The system is in equilibrium.
The clockwise moments equal the anti-clockwise moments. The system is in equilibrium.