Basic Math Operations - Mathematics and Statistics for the Environment - page 67

r = 10 ft

H = 25 ft

FIGURE 2.9

Circular or cylindrical water tank.

2.12 FORCE, PRESSURE, AND HEAD CALCULATIONS
Before we review calculations involving force, pressure, and head, we must first define these terms:

• Force— The push exerted by water on any confined surface. Force can be expressed in
pounds, tons, grams, or kilograms.
• Pressure— The force per unit area. The most common way of expressing pressure is in
pounds per square inch (psi).
• Head— The vertical distance or height of water above a reference point. Head is usually
expressed in feet. In the case of water, head and pressure are related.

2.12.1 F orCe and p ressure
Figure 2.10 helps to illustrate these terms. A cubical container measuring 1 foot on each side can
hold 1 cubic foot of water. A basic fact of science states that 1 cubic foot of water weights 62.4 lb
and contains 7.48 gal. The force acting on the bottom of the container is 62.4 lb/ft 2 . The area of the
bottom in square inches is

1 ft 2 = 12 in. × 12 in. = 144 in. 2

62.4 lb
of
water

1 ft

1 ft

1 ft

FIGURE 2.10 One cubic foot of water weighs 62.4 lb.