Equilibrium of forces

📋 Teacher notes

• •Equilibrium means the resultant (net) force is zero — it does NOT mean the object is at rest. A common exam trap.
• •STATIC equilibrium: net force = 0 AND the object is at rest (stays at rest).
• •DYNAMIC equilibrium: net force = 0 but the object is already moving — it continues at constant velocity (Newton’s 1st law).
• •If the forces are unbalanced, the object accelerates — it does not matter whether it started at rest or already moving.
• •Real examples of dynamic equilibrium: a car at cruising speed (driving force = resistive forces), a skydiver at terminal velocity (weight = air resistance).