Explanation:

Irrotational motion is a type of fluid motion in which the fluid particles move in a manner that the circulation around any path is zero. The following points explain the characteristics of an irrotational motion:

Fluid element does not undergo any shear:

- In an irrotational motion, the fluid particles move in a manner that they do not undergo any shear.
- Shear is a type of deformation in which the adjacent layers of fluid particles move parallel to each other at different velocities.
- As there is no shear in irrotational motion, the fluid particles move in a manner that their velocities vary only in magnitude and not in direction.

Fluid particles do not undergo a circular motion:

- In irrotational motion, the fluid particles move in a manner that they do not undergo a circular motion.
- Circular motion is a type of motion in which the fluid particles move along a circular path.
- As there is no circular motion in irrotational motion, the fluid particles move in a manner that their velocities vary only in magnitude and not in direction.

Circulation around any path is zero:

- The most important characteristic of irrotational motion is that the circulation around any path is zero.
- Circulation is a measure of the rotation of fluid particles around a closed path.
- In irrotational motion, the fluid particles move in a manner that their velocities vary only in magnitude and not in direction. As a result, the circulation around any path is zero.

Viscosity may not be zero:

- Viscosity is a measure of the resistance of a fluid to flow.
- The viscosity of a fluid may or may not be zero in irrotational motion.
- However, the irrotational motion assumes that the fluid is inviscid, which means that the fluid has zero viscosity.

Conclusion:

Irrotational motion is a type of fluid motion in which the fluid particles move in a manner that the circulation around any path is zero. The fluid elements do not undergo any shear, and the fluid particles do not undergo a circular motion. The viscosity of a fluid may or may not be zero in irrotational motion.