Using Moments with Equilibrium (Edexcel A Level Maths): Revision Note

Using Moments - Equilibrium

What happens with moments if a rigid body is in equilibrium?

• If a rigid body is in equilibrium then:

  • The resultant force is 0 N

  • The resultant moment about any point is 0 N m

• The sum of the magnitudes of the clockwise moments equals the sum of the magnitudes of the anti-clockwise moments

How do I solve problems involving moments and equilibrium?

• Step 1: Identify all forces and perpendicular distances from the pivot

• Step 2: Use the fact that the resultant force is 0 N to form an equation

• Step 3: Use the fact that the resultant moment about any point is 0 N m to form equations

  • If there is an unknown force you can choose a pivot that is on the line of action of that force – this will mean that the moment of that force is 0 N m

• Step 4: Solve the equations