1. Is water necessary for industry? Explain.

2. What great property do liquids possess that solids do not? What use is made of water in industry?

3. A liquid is often used as a part of machinery. What property is utilized?

4. How can the pressure of a liquid on the surface be ascertained?

5. Will the perpendicular sides of a trough filled with liquid sustain the same pressure, whether the trough be narrow or wide?

6. Explain the principle of science underlying hydraulic machines.

7. Name some of the applications of hydraulic machines.

8. Why does deep sea diving often cause pain and bleeding in the ears and nose?

9. Explain the importance of a knowledge of the principle of specific gravity in the trades.

10. Explain how a modern warship floats although made entirely of steel, its walls being of steel plate from 6 to 18 in. thick.

11. What is the water-line of a boat?

12. A boat passes from fresh into salt water. Will the water-line rise or fall?

### Problems

1. What is the weight of a rectangular block of hardwood with the dimensions 8 ft. 4 in. X 7 ft. 6 in. X 3 ft. 3 in.? The specific gravity of wood is .7. The weight of a cubic foot of water is 62.5 lbs.

2. What is the weight of a cylindrical block of soft seasoned wood 8 in. in diameter and 4 ft. long? The specific gravity is .5. The weight of a cubic foot of water is 62.5 lbs.

3. What is the weight of salt water in a rectangular tank 5 ft. 2 in. X 4 ft. 7 in. X 3 ft. 5 in.? The specific gravity of salt water is 1.03 and the weight of a cubic foot of water is 62.5 lbs.

4. Express in pounds per square inch a "bend of 69 ft."

5. What is the pressure near the keel of a vessel drawing 18 ft. of water. (Salt water has specific gravity 1.03.)

6. A hole is cut in the bottom of a ship drawing 17 ft. of water. What force is necessary to hold a plank tightly against the hole?

7. It is desired to have a pressure of 60 lbs. at a hydrant. How high must the reservoir be above the main?

8. A rowboat weighs 230 lbs. How many cubic feet of water does it displace? A cubic foot of water weighs 62.5 lbs.

9. The cork of a life preserver weighs 19 lbs. What is the volume in cubic inches? The specific gravity of cork is 0.25.

10. Elevators are often run by water pressure obtained from the local water system. If the pressure on the main is 55 lbs. and the diameter of the plunger of an elevator is 11 in., how heavy a load can the elevator lift if the friction loss is 30%?

11. Soundings at sea are made by lowering a form of pressure gauge. If a pressure gauge reads 65 lbs., what is the depth? (Consider the density of sea water 1.026.)

12. What is the weight of a cylindrical piece of lead 4 ft. long with a diameter of 3 in.? The specific gravity of lead is 11.4 and the weight of a cubic foot of water is 62.5 lbs.

13. What is the weight of concentrated sulphuric acid (specific gravity 1.84) contained in a cylindrical jar 8 in. in diameter and 2 1/2 in. high? A cubic foot of water weighs 62.5 lbs.

14. Determine the weight of gasolene in a rectangular tank 3 ft. 7 in. X 2 ft. 2 in. X 1 ft. 8 in., if the specific gravity is .7 and a cubic foot of water is equal to 62.5 lbs.

15. The inside diameter of a lead pipe is 1 in. and the thickness of pipe is 1/4: in. How many pounds in a foot of pipe? The specific gravity of lead is 11.4 and a cubic foot of water weighs 62.5 lbs.

16. What are some of the principles of science underlying the hydraulic machine?

17. What are some of the uses of hydraulic machines?

18. (a) What is the weight of a cubic inch of water if a cubic foot weighs 62.5 lbs.

(b) How may the weight of a cubic inch of a substance be determined, if the specific gravity of the substance is known?

19. In making solder (composed of lead and tin), the tin melts first and then floats on top. Why?