Mechanical Engineering - Hydraulics and Fluid Mechanics - Discussion

Viscosity/Dynamic viscosity of mercury is higher than water and Kinematic viscosity of water is higher than mercury.

Viscosity of mercury is lesser than that of water because shear stress developed in water is more than Mercury this is taken from the relation viscosity is directly proportional to the shear stress and inversely proportional to the velocity gradient.

Viscosity means Dynamic viscosity, according to which, Hg is more viscous than water, But when it comes to kinematic viscosity (viscosity/ density), Hg has less kinematic viscosity. In the asked question, it is given as viscosity, meant Dynamic viscosity for which, Hg is more viscous. Hence answer is wrong.

There are two types of viscosities they need to mention.

1. Kinematic viscosity.
2. Dynamic viscosity.

Kinematic viscosity of water is greater than kinematic viscosity of mercury.

Dynamic viscosity of mercury is greater than dynamic viscosity of water.

Kinematic viscosity of water is higher than that of mercury.
But dynamic is less than of mercury.
Because of the density of mercury is higher (13593) than of water (997).

Viscosity of water is less than that of mercury.

Viscosity of water is less than that of Mercury, while kinematic viscosity of water is greater than that of Hg. Because it is viscosity/density.

There are two types of viscosity one is kinematic viscosity and other one is dynamic viscosity.

Kinematic viscosity is the dynamic viscosity divided by his dense. And mercury has high denser than water. Therefore kinematic viscosity of mercury is less than water. That's why if you fall down mercury from glass it is speedy falls down than water.

In mercury, molecules are more cohesion than water molecules however water molecules have hydrogen bond while mercury have metallic bond. And metallic bond is strong than hydrogen bond. So mercury molecules resist force more than water molecules. That's why dynamic viscosity of mercury is greater than water.

Metallic bond is stronger than Hydrogen bond so mercury resist more force than water.

Hence mercury has more dynamic viscosity than water.

Kinematic viscosity of water is greater than mercury due to lower density but dynamic viscosity of water is lower than that of mercury.