Figure 1.5 shows a container of liquid with a movable piston supporting a load. Compute the magnitude of the pressure in the liquid under the piston if the total weight of the piston and the load is 800 N and the area of the piston is 3000 mm2.

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Accepted Answer

It is reasonable to assume that the entire surface of the fluid under the piston is sharing in the task of supporting the load. The second of Pascal’s laws states that the fluid pressure acts perpendicular to the piston. Then, using Eq. (1–3) , we have

[latex]P= \frac{F}{A} = \frac{800N}{3000mm^2} = 0.27{N}/{mm^2}[/latex]

The standard unit of pressure in the SI system is the[latex]{N}/{m^2}[/latex] ,called the pascal (Pa) in honor of Blaise Pascal. The conversion can be made by using the factor [latex]10^3mm= 1m.[/latex]We have

[latex]P= \frac{0.27N}{mm^2} imes \frac{\left(10^3 mm ight)^2 }{m^2} = 0.27 imes 10^6 {N}/{m^2}= 0.27MPa[/latex]

Note that the pressure in [latex]{N}/{mm^2}[/latex] is numerically equal to pressure in MPa. It is not unusual to encounter pressure in the range of several megapascals (MPa) or several hundred kilopascals (kPa).

Pressure in the U.S. Customary System is illustrated in the following example problem.

Question 1.2: Figure 1.5 shows a container of liquid with a movable piston...

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