A liquid kept in a bucket is stirred for few seconds and then kept at rest. The liquid comes in rest after some time due to-

CONCEPT:

• Viscous force (F): When a layer of fluid slips or tends to slip on adjacent layers in contact, the two layers exert tangential force on each other which tries to oppose the relative motion between them.
  • The property of a fluid due to which it opposes the relative motion between its different layers is called viscosity (or fluid friction or internal friction) and the force between the layers opposing the relative motion is called viscous force.
• The force acting between the different layers of a fluid is given by:

\(F = - \eta A\frac{{dv}}{{dx}}\)

Where η = coefficient of viscosity, A = area of the plane and dv/dx = velocity gradient.

• A negative sign is employed because viscous force acts in a direction opposite to the flow of liquid.

EXPLANATION:

• When a liquid kept in a bucket is stirred for a few seconds and then kept at rest, then the liquid comes to rest after some time due to viscosity because different layers of liquid in a bucket oppose the relative motion. Therefore option 2 is correct.