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# Viscous Force or Viscosity

Each liquid moves with a different speed. Water flows faster than other liquids. Coconut oil flows with a moderate speed.

Viscous Force or Viscosity

Activity 8

Take a small quantity of different kinds of liquid like coconut oil, honey, water and ghee etc. , Place one drop of each liquid on a separate glass plate. Now gently raise one end of the glass plate, so as to allow the liquid to slide down the smooth surface of the plate. Observe the speed of each liquid.

Aim : To understand about the frictional force between the layers of liquid in motion.

Materials required : Different kinds of liquid (coconut oil, honey, water, ghee), glass plates - 4 nos.

Procedure :

(i) Take a small quantity of different kinds of liquid like coconut oil, honey, water  and ghee etc., in a cup.

(ii) Place one drop of each liquid on a separate glass plate.

(iii) Next, gently raise one end of the glass plate, one by one, so as to allow the liquid to slide down the smooth surface of the plate.

(iv) Observe the speed of each liquid.

Observation : Each liquid moves with a different speed. Water flows faster than other liquids. Coconut oil flows with a moderate speed. Ghee flows very slowly.

Inference : Between the layers of each liquid, in motion, there is a frictional force parallel to the layers of the liquid. This frictional force opposes the motion of the liquid layers while they are in motion.

Each liquid moves with a different speed. Water flows faster than other liquids. Coconut oil flows with a moderate speed. Ghee flows very slowly. Between the layers of the liquid, which is in motion, there is a frictional force parallel to the layers of the liquid. This frictional force opposes the motion of the liquid layers while they are in motion.

The frictional force acting between the successive layers of the liquid which acts in order to oppose the relative motion of the layer is known as viscous force. Such a property of a liquid is called viscosity. Viscous force is measured by the unit called poise in CGS system and kgm–1s–1 or Nsm–2 in SI system.

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