![]() (iv) The cloud particles fall down very slowly because of the viscosity of air and hence appear floating in the sky. The reason is again viscosity which is very small for air but comparatively much larger for water. (iii) We can walk fast in air, but not in water. As honey tends to flow down under gravity, the relative motion between its layers is opposed strongly. This is because honey is much more viscous than water. (ii) If we pour water and honey in separate funnels, water comes out readily from the hole in the funnel while honey takes enough time to do so. If we pour coaltar and water on a table, the coaltar will stop soon while the water will flow upto quite a large distance. have a larger viscosity than thinner ones like water. Thicker liquids like honey, coaltar, glycerine, etc. (i) A stirred liquid, when left, comes to rest on account of viscosity. The property of viscosity is seen in the following examples: The property of the liquid by virtue of which it opposes the relative motion between its adjacent layers is known as viscosity. In the absence of the external force, the viscous forces would soon bring the liquid to rest. If the flow of the liquid is to be maintained, an external force must be applied to overcome the dragging viscous forces. These forces are called ‘viscous forces’. This means that in between any two layers of the liquid, internal tangential forces act which try to destroy the relative motion between the layers. Similarly, each layer tends to increase the velocity of the layer below it. Thus each layer tends to decrease the velocity of the layer above it. The layer a tends to retard the layer b, while b tends to retard c. Their velocities are in the increasing order. Let us consider three parallel layers a, b and c. Thus there is a relative motion between adjacent layers of the liquid. In the figure, the lengths of the arrows represent the increasing velocity of the layers. The layer of the liquid which is in contact with the surface is at rest, while the velocity of other layers increases with distance from the fixed surface. Suppose a liquid is flowing in streamlined motion on a fixed horizontal surface AB. This force is called ‘internal frictional-force’. Similarly, when a layer of a liquid slides over another layer of the same liquid, a frictional-force acts between them which opposes the relative motion between the layers. This force opposes the relative motion of the bodies. ![]() When a solid body slides over another solid body, a frictional-force begins to acts between them.
0 Comments
Leave a Reply. |