15. Find the force on the bottom of a water tank 14 ft. in diameter when the water is 15 ft. deep, when full of water.
16. Find the force on one side of a cistern 8 ft. deep and 10 ft. square, when full of water.
17. Find the force on a vertical dam 300 ft. long and 10 ft. high, when full of water.
18. Find the pressure at the bottom of the dam in question 17.
19. Why are dams made thicker at the bottom than at the top?
20. A ship draws 26 ft. of water, i.e., its keel is 26 ft. under water. What is the liquid force against a square foot surface of the keel? Find the pressure on the bottom.
(2) Transmission of Liquid Pressure
40. Pascal's Principle.—Liquids exert pressure not only due to their own weight, but when confined, may be made to transmit pressure to considerable distances. This is a matter of common knowledge wherever a system of waterworks with connections to houses is found, as in cities. The transmission of liquid pressure has a number of important applications. The principle underlying each of these was first discovered by Pascal, a French scientist of the seventeenth century. Pascal's Principle, as it is called, may be illustrated as follows:
Suppose a vessel of the shape shown in Fig. 18, the upper part of which we may assume has an area of 1 sq. cm., is filled with water up to the level AB. A pressure will be exerted upon each square centimeter of area depending upon the depth. Suppose that the height of AB above CD is 10 cm., then the force upon 1 sq. cm. of CD is 10 g., or if the area of CD is 16 sq. cm., it receives a force of 160 g.
