Question

A gale is in a house. The force on the roof due to the gale is:
A. Directed downward
B. Zero
C. Directed upward
D. Information insufficient

Answer 1

The above-given statement is one of the applications of Bernoulli's theorem. It states that the sum of pressure energy, kinetic energy and potential energy per unit mass is always constant for an ideal fluid that is incompressible and non-viscous.

Complete step by step answer:
A gale is an extreme wind. During the gale, the velocity of air just above the roof is large. So according to Bernoulli's theorem, the pressure just above the roof is less than the pressure below the roof. Due to this pressure difference, an upward force acts on the roof, which is blown off without damaging other parts of the house. Due to Bernoulli's principle, the pressure above the upper surface decreases and the pressure below the lower surface increases. This pressure difference helps in lifting the roof of houses.

Therefore, the correct option is (C).

Note: Bernoulli's theorem is based on the law of conservation of energy. It states that the energy must be conserved and can be converted from one form to another. Significant applications of Bernoulli's theorem include venturimeter, an atomizer (or sprays), spinning of a ball, etc. Consider the case of a spray. The pressure inside it decreased as the air already rushed out as we pressed the bottle. To balance the decreased pressure energy, the level of the liquid rises in the can and it comes out along with the air in an attempt to balance the gravitational energy part.