Physics [2 Mark Question Answer]

Examples of couple action in daily life:
(i) Opening and closing the cap of a bottle
(ii) Turning a key in a lock

Conditions for equilibrium:
(a) Vector sum of forces acting on the body should be zero.
(b) Algebraic sum of moments acting on the body should be zero.

A body is said to be in equilibrium under the action of a number of forces, if the forces are not able to produce any change in the state of rest or of uniform motion or uniform rotation.
Equilibrium is a state of zero acceleration.

This is so because near the free end, the distance of the point of application of force from the axis of rotation becomes maximum, so the torque (= Force x perpendicular distance of the pivot from the force) is very large and hence it is easier to open the door.

Moment of force, torqu, τ = 4Nm
Apllied force, F = 10N
Distance from pivot, d =?
τ = F x d
⇒ d = τ / F = 4 / 10 = 0.4m

Given, applied force, F = 20N
Distance From the pivot , d = 40cm = 0.4m
Torque = F x d = 20 x 0.4 = 8 Nm

The turning effect of a couple is called the moment of couple and is calculated by the product of either of the forces and the perpendicular distance between them. Its SI unit is Nm.