Chemical Engineering - Fluid Mechanics - Discussion

Because the surface tension is force/length.

Hello Sachin !

surface tension of any fluid particle acts radially over the tangential components so that the fluid particles try to obtain a minimal surface area. In this stake the mercury droplet gets spherical and thus have minimum contact just at only one point on the glass

It should be force of adhesion, because force of adhesion works between two different surfaces.

The reason we consider the surface area of the entire mass of mercury, including the part of the surface that is in contact with the glass, is because mercury does not adhere at all to glass. So the surface tension of the mercury acts over its entire surface area, including where it is in contact with the glass. If instead of glass, the tube were made out of copper, the situation would be very different.

The reason should be the force of cohesion. It is because adhesion is the property by which things gets wet after having a contact with the liquid while surface tension makes the surface intact. Cohesion is the force responsible for surface tension and therefore it restricts the liquid from adhering with the other surfaces. Cohesion is the force among the molecules of the same matter.

It is the cohesion force that predominates in mercury and hence the molecules of mercury tend to remain together as cohesion is attractive force between like particles. Hence the glass surface doesn't get wet.

Mercury does not wet glass - the cohesive forces within the drops are stronger than the adhesive forces between the drops and glass. When liquid mercury is confined in a tube, its surface (meniscus) has a convex shape because the cohesive forces in liquid mercury tend to draw it into a drop.

Surface tension is also important at the interface between a liquid, a gas, and a solid. For example, a meniscus occurs when the surface of a liquid touches a solid wall, as most readily noticed when a capillary tube is placed in a liquid. Consider a glass capillary tube inserted into a liquid, such as water. The water will rise up the tube to a height, h, because surface tension pulls the surface of the water towards the glass, as shown. The meniscus is the curved surface at the top of the water column.

The contact angle is defined as the angle between the liquid and solid surface, as shown in the sketch. Contact angle depends on both the liquid and the solid. If theta is less than 90°, the liquid is said to "wet" the solid. However, if theta is greater than 90°, the liquid is repelled by the solid, and tries not to "wet" it. For example, water wets glass, but not wax. Mercury does not wet glass.

Water wets glass Mercury does not wet glass.

Hello friends.

According to me it should be surface tension because surface tension is also cause of force of adhesion.

Dear friends,

A/c to me, surface tension is responsible for this case. Cohesion b/w molecules of mercury is greater than adhesion b/w mercury and glass and theta is equal to 128 degree.