2. 1© Manhattan Press (H.K.) Ltd. Torque Couple Couple 1.4 Moment of a force

3. 2 © Manhattan Press (H.K.) Ltd. Torque 1.4 Moment of a force (SB p. 62) Torque ( or moment of a force) = F x r Object pivoted at O and free to rotate about O Force (F) acts on it, it rotates Torque (or moment of a force) – turning effect of a force perpendicular distance Unit – N m

4. 3 © Manhattan Press (H.K.) Ltd. Torque 1.4 Moment of a force (SB p. 62) Rotate anti-clockwise – assumed as positive Rotate clockwise – negative Torque (magnitude, direction) - vector

5. 4 © Manhattan Press (H.K.) Ltd. Torque 1.4 Moment of a force (SB p. 62) Daily examples:

6. 5 © Manhattan Press (H.K.) Ltd. Couple 1.4 Moment of a force (SB p. 63) A couple consists of two forces of the same magnitude but acting in opposite directions and not along the same line. Go to Common Error

7. 6 © Manhattan Press (H.K.) Ltd. Couple 1.4 Moment of a force (SB p. 63) Sum of moments about O = F ×OB + F ×OA = F ×(OB + OA) = F ×AB

8. 7 © Manhattan Press (H.K.) Ltd. Couple 1.4 Moment of a force (SB p. 63) Note: A couple has no resultant force. It only produces a turning effect. Torque of a couple = One of the forces × Perpendicular distance between the two forces = F ×AB Go to More to Know 8 More to Know 8

9. 8 © Manhattan Press (H.K.) Ltd. End

10. 9 © Manhattan Press (H.K.) Ltd. A couple is not an action and reaction pair as the two forces of couple act on the same object. Return to Text 1.4 Moment of a force (SB p. 63)

11. 10 © Manhattan Press (H.K.) Ltd. In daily life, your hands on a steering wheel can provide a couple to turn the wheel. Torque = F × d Return to Text 1.4 Moment of a force (SB p. 63)