The spherical shape of the liquid drops is because of surface tension. The liquid tends to decrease the surface area, since the sphere has minimum surface area for particular volume of the liquid, thus liquid drops are spherical in shape.
Capillary action
If a capillary tube is dipped in a liquid like water which wets the glass, the liquid rises into a capillary tube to a certain height. This rise in glass tube is known as Capillary Action. This is because of surface tension, the inward pull acting on the surface molecules pushes the liquid into the capillary tube.
If liquid is such which does not wet the walls of glass like Mercury, then level of Mercury in capillary falls. This is due to the fact that in case of Mercury or such liquids cohesive forces are stronger than Adhesive forces.
Viscosity
It is well known that all liquids do not flow with the same speed. Some liquids like water, alcohol, ether etc. flow very rapidly while some liquids like glycerine, honey, castor oil etc. flow slowly .This indicates that every liquid has some internal resistance to flow.
This internal resistance to the flow possessed by a liquid is known as its Viscosity.
To understand the nature of internal resistance or friction existing within a liquid. It has been observed that liquid flows in layers. The layer which is in contact with the wall of tube through which it flows is almost stationary. As we move towards higher level, the speed increases. In other words, every layer offers some resistance or friction to the layers flowing over it. Thus viscosity may also be defined as,
“The force of friction or resistance offered by a layer of liquid to the other layer flowing over it.”
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