Calculating pressure

Custom Search

Pressure

Basic Machines

Measuring fluid pressure

CALCULATING PRESSURE

To calculate pressure, divide the force by the area on which you apply force. Use the following formula:

To understand this idea, follow this problem. A fresh water holding tank aboard a ship is 10 feet long, 6 feet wide, and 4 feet deep. Therefore, it holds 10 x 6 x 4, or 240, cubic feet of water. Each cubic foot of water weighs about 62.5 pounds. The total force outside the tanks bottom is equal to the weight of the water: 240 x 62.5, or 15,000 pounds. What is the pressure on the bottom of the tank? Since the weight is even on the bottom, you apply the formula and substitute the proper F and A. In this case, F= 15,000 pounds; the area of the bottom in square inches is 10 x 6 x 144, since 144 square inches = 1 square foot.

Now work out the idea in reverse. You live at the bottom of the great sea of air that surrounds the earth. Because the air has weightgravity pulls on the air toothe air exerts a force on every object that it surrounds. Near sea level that force on an area of 1 square inch is roughly 15 pounds. Thus, the air-pressure at sea level is about 15 psi. The pressure gets less and less as you go up to higher altitudes.

With your finger, mark out an area of 1 square foot on your chest. What is the total force pushing on your chest? Again use the formula . Now substitute P and 144 square inches for A. Then, F = 144 x 15, or 2,160 pounds. The force on your chest is 2,160 pounds per square foot-more than a ton pushing against an area of 1 square foot. If no air were inside your chest to push outward with the same pressure, youd be flatter than a brides biscuit.