Moments & Equilibrium — A/L Physics

What must I remember about Moments & Equilibrium?

• Moment (Torque) of a Force: Tendency of a force to produce rotation about a pivot; Moment τ = Force * Perpendicular distance from pivot to line of action (τ = F * d_perp).
• Couple: Two equal, opposite, and non-collinear parallel forces; Torque of a couple = One force * Perpendicular distance between lines of action (τ = F * d); independent of reference point.
• Conditions for Static Equilibrium: 1) Translational equilibrium: Resultant vector sum of forces must be zero (∑ Fx = 0, ∑ Fy = 0); 2) Rotational equilibrium: Resultant sum of moments about ANY arbitrary axis must be zero (∑ τ = 0).
• Center of Gravity (CG): The unique single point through which the resultant gravitational force (weight) of the entire body acts for all spatial orientations.

Test yourself (1 minute)

1. Three Non-Parallel Forces in Equilibrium

   The lines of action of three non-parallel forces in equilibrium MUST be concurrent (intersect at a single common point) and coplanar.

2. Center of Mass vs Center of Gravity

   Center of Mass (COM) depends purely on mass distribution; Center of Gravity (CG) coincides with COM only in a uniform gravitational field.

3. Stability of Equilibrium

   Stable (CG rises on small displacement), Unstable (CG falls), Neutral (CG height remains constant).

Practise Moments & Equilibrium questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 2: Mechanics

What should I study first?

What comes next?

Next in the syllabus

Where does Moments & Equilibrium fit in the syllabus?

Unit 2.3 · Year 1 · Term 1