$$\text{Moment} = \text{force}\times\text{perpendicular distance from the pivot} \quad (\text{N m})$$ Principle of moments: at equilibrium $$\text{sum of clockwise moments} = \text{sum of anticlockwise moments}$$ $$F_1 d_1 = F_2 d_2$$

• For a body in equilibrium: total upward force $=$ total downward force.
• For a uniform rod, the weight acts at its midpoint (the centre of gravity).
• Couple: moment $= F \times$ (perpendicular distance between the two forces).