A moment is a force applied about a distance. The moment $m$ of a force $F$ about a point with a perpendicular distance of $d$ can be resolved by the equation:

$$m = F \times d$$

The principle of moments

This is a fundamental law of physics that states that the sum of the moments going clockwise must equal the sum of the moments going anticlockwise. This can be represented by the equation:

$$m_1 = m_2 F_1 \times c_1 = F_2 \times c_2$$

Centre of mass

The centre of mass of an object is the point at which one of the forces has no turning effect. This can be calculated:

• Mathematically if you know the object is uniform and you know its dimensions.
• Scientifically by doing the plum line experiment with the object.