Moment of force or Torque | Physics class 10

Moment of Force – The physical quantity that produces the turning effect on the body about an axis is called the moment of force or torque.

Moment of force

Measurement of torque – The moment of torque is equal to the product of the magnitude of the force and the perpendicular distance of the line of action of a force from the axis of rotation.

Mathematical Expression:

Moment of force  = Force × perpendicular distance.

or, Moment of force =  F × OP

Unit of moment of force :

  • In SI unit, unit of moment of force is ‘Newton metre‘ (N m)
  • In CGS unit, unit of moment of force is ‘dyne cm‘.

Factors affecting the turning of a body :

(i) The magnitude of the applied force, and

(ii) the perpendicular distance of the line of the force from the pivoted point.

Types of moments

(i) Clockwise moment – If the effect on the body is to turn it anticlockwise, moment of force is called the anticlockwise moment.

(ii) Anticlockwise moment –  If the effect on the body is to turn it clockwise, moment of force is called the clockwise moment.

anticlockwise moment

* Note – the anticlockwise moment is taken as positive and the clockwise moment is taken as negative.

Some common examples of moment of force 

(i) turning of the steering wheel,

(ii) opening of the door,

(iii) using of a spanner to tighten or loosen a nut.

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