Question

Comparing Example 12.1 (Section 12.1) and Example 12.2 (Section 12.2), it seems that 700 N of air is exerting a downward force of on the floor. How is this possible?

Short answer

The floor would not collapse due to the presence of upward force exerted by the air pressure underneath the floor.

Step-by-step solution

Given Data

The force of the air is 700 N.

The downward force on the floor is.

Understanding the relation of pressure and force

In this problem, the concept of pressure and force is used. If the pressure is constant on the fluid then the resulting normal force can be calculation by using the relation,

F = PA

Comparing the examples to evaluate the downward force exerting on the floor

In the example 12.1, it is evaluated that the weight of the room full of air is equivalent to the weight of an average adult. As compared to air, water has more density because of which its mass or weight is higher. Also, the floor of an ordinary house will collapse due to the weight of a room full of water.

In the example 12.2, it is evaluated that the floor will not collapse due to the weight of the water unlike example 12.1 because an upward force of similar magnitude is exerted on the floor. The air present underneath the floor exerts this upward force. Also, if the thickness of the floor is neglected, the total force exerted by the air pressure will be equivalent to zero.