Chapter U3, Problem 1STP

Interpretation Introduction

Interpretation:

The option which has only units of pressure needs to be identified.

Concept introduction:

Pressure (P) is the force (F) exerted per units area (A) of a surface i.e.

$\text{Pressure (P) = }\frac{\text{Force (F)}}{\text{Area (A)}}\text{ -----(1)}$

The units of pressure are derived from the units of force and area.

Answer to Problem 1STP

(A) atm, lb/in² and in Hg

Explanation of Solution

Based on equation (1):

$\text{P = }\frac{\text{F}}{\text{A}}$

One of the units of force (F) is pounds (lb)

Area (A) can be expressed in square inches i.e. in²

Hence:

$\text{P = }\frac{\text{F}}{\text{A}}={\text{'lb/in}}^2\text{'}$

The net pressure experienced at every point on the earth's surface is expressed in terms of atmospheric pressure i.e. in units of 'atm'

Atmospheric pressure is usually measured using mercury (Hg) barometers which contains a Hg column of nearly 30 in height. Hence, the pressure can also be expressed in terms of inches of Hg i.e. 'in Hg'.

Conclusion

Therefore, the units of pressure are: atm, lb/in² and in Hg.