Explain in detail the functionality of a hair hygrometer and sling psychrometer in measuring relative humidity. Illustrate this with a diagram. What are the forces acting on a vertically moving parcel...

Explain in detail the functionality of a hair hygrometer and sling psychrometer in measuring relative humidity. Illustrate this with a diagram.

What are the forces acting on a vertically moving parcel of air? How are they affected by the density of the air parcel?