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Calculating moments

The moment of a force can be calculated using the formula $$$ \Tblue{\text{moment}} = \Tred{\text{force}} \times \Tgreen{\text{perpendicular distance to pivot}}$$$

The perpendicular distance is the length of a line drawn between the vector representing a force and the pivot, at right angles to the force.

The perpendicular distance is greatest if the force is at right angles to the object.

The SI unit of a moment is the newton metre and has the symbol $$\text{Nm}.$$

If you apply a $$\Tred{10\text{ N}}$$ force on a door at a point $$\Tgreen{0.5 \text{ m}}$$ away from the pivot, the moment is equal to $$\Tred{10\text{ N}} \times \Tgreen{0.5 \text{ m}} = \Tblue{5 \text{ Nm}}.$$

The force in the picture is not at right angles to the object. The perpendicular distance of $$0.2 \um$$ must be used to calculate the moment. Do not use $$0.3 \um.$$

The force on the beam is on the left hand side of the pivot. It causes a moment of $$3 \text{ Nm} \text{ anti-clockwise}.$$
The force on the beam is on the left hand side of the pivot. It causes a moment of $$3 \text{ Nm} \text{ anti-clockwise}.$$