6. What is the liquid force on one side of a liter cube full of water? Full of alcohol? Full of mercury? What force is pressing on the bottom in each case? 7. What depth of water will produce a pressure of 1 g. per square centimeter? 10 g. per square centimeter? 1000 g. per square centimeter? 8. What depth of water will produce a pressure of 1 lb. per square inch? 10 lbs. per square inch? 100 lbs. per square inch? 9. What will be the force against a vertical dam-breast 30 meters long, the depth of the water being 10 meters? 10. A trap door with an area of 100 sq. dcm. is set in the bottom of a tank containing water 5 meters deep. What force does the water exert against the trap door? 11. What is the force on the bottom of a conical tank, filled with water, the bottom of which is 3 meters in diameter, the depth 1.5 meters? 12. If alcohol, density 0.8 were used in problem 11, what would be the force? What would be the depth of alcohol to have the same force on the bottom as in problem 11? 13. What is the pressure in pounds per square inch at a depth of 1 mile in sea water, density 1.026 grams per cc.? 14. Find the force on the sides and bottom of a rectangular cistern filled with water, 20 ft. long, 10 ft. wide, and 10 ft. deep? 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. [Illustration: FIG. 18.--The force increases with the depth.]