Home » Handbook of O Level Physics » UNIT 5: TURNING EFFECT OF FORCES


  • Moment of a force: It is the product of force and the perpendicular distance (between the line of action of the force and the pivot).

Moment of a force = F x d

  • Moments can be clockwise or anticlockwise.

  • The Principle of Moments: For a body in equilibrium, the sum of clockwise moments is equal to the sum of anticlockwise moments.

    • Example:

  • Centre of mass: It is the point through which the whole weight of an object seems to act for any orientation of the object.

    • Centre of mass of an object (such as ring) can lie outside the object.

    • Experiment to determine centre of mass of a plane lamina

      • The marking points are:

        • set metal swinging (to ensure minimal friction at pivot)

        • allow to come to rest

        • use of plumb line from hole

        • mark line along plumb line (on metal)

        • hang from another hole

        • hang from 3 rd hole

        • point of intersection of lines is centre of mass

  • Stability: It is the ability of an object to regain its original position after it has been tilted slightly.

    • Stability can be improved by

      • lowering the centre of mass

      • increasing the broadness of base

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