TRAVEL ON WATER 



307 



When it is to 'be submerged, water is pumped into 

 tanks, thus adding weight to the boat. Submerging 

 is aided by means of fins which can be tilted in such 

 a manner as to throw the front end down. When the 

 boat is to be brought to the surface compressed air is 

 forced into the tanks and the water is forced out. This 

 makes the boat a floating body, and it rises under the 

 influence of the buoyant force of the surrounding 

 water. The rising of the boat to the surface is also 

 aided by so tilting the fins that the front end of the 

 boat is thrown upward. When a submarine is on the 

 surface it is propelled by Diesel engines and when 



International Newsreel 



FIG. 513. THE U. S. NAVAL SUBMARINE NdUtUuS 



submerged it is propelled by motors run from storage 

 batteries. 



Exercise. Infer a reason why the submarine uses elec- 

 tric motors rather than its Diesel engines for power when 

 it is submerged. 



REFERENCES FOR FURTHER STUDY 

 Texts 



Caldwell and Curtis, Science for Today, Chap. 28 

 Clement, Collister, and Thurston, Our Surroundings, Chap. 



20 (part) 

 Hunter and Whitman, Science in Our World of Progress, 



Unit 9 

 Lake, Harley, and Welton, Exploring the World of Science, 



Chap. 25 (part) 

 Pieper and Beauchamp, Everyday Problems in Science, Unit 



17 

 Van Buskirk and Smith, The Science of Everyday Life, Chap. 



20 



Webb and Beauchamp, Science by Observation and Experi- 

 ment, Unit 3 

 Wood and Carpenter, Our Environment: How We Use and 



Control It, Topic 11 B 



Special references 



Bachman, Great Inventors and Their Inventions 

 Campion's Pictured Encyclopedia 

 Chatterton, The Romance of the Ship 



Collins and Collins, Boys' Book of Submarines 

 Miller, Canoeing, Sailing, and Motor Boating 

 Bishop, The Story of the Submarine 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1 . Something of the development of water transporta- 

 tion. 



2. An understanding of the principle of Archimedes. 



3. An understanding of the principle of stability and 

 the factors which control it. 



4. An understanding of how modern ships secure their 

 power. 



5. A knowledge of the importance of the gyro com- 

 pass to modern water transportation. 



6. An understanding of how the submarine applies 

 the principle of Archimedes. 



TEST OF MASTERY OF THE TOPIC 



In your notebook complete the statements, answer the 

 questions and comply with the instructions. 



1. The lifting force of water is called 



2. Floating bodies appear to lose their weight when 



placed in water. 



3. and are used to furnish power for modern 



ships. 



4. Explain what is meant by center of gravity. 



5. When submerged in water sinking bodies appear to 

 lose weight equal to the . of _^ displaced. 



6. Stability means when referring to a ship. 



7. The stability of a boat in water depends largely upon 

 the of the center of gravity. 



8. The gyroscope is used on ships to prevent . 



9. The use of the gyroscope for this purpose depends 



upon its tendency to any change of of its axis 



of spin. 



10. When a submarine is under water it is driven by 



run from large . 



11. The of the submarine aid in rising and sub- 

 merging. 



12. discovered the principle of buoyancy. 



13. Ships are driven through the water by means of . 



propellers. 



14. Ships are steered by means of 



15. Write a paragraph setting forth the important stages 

 in the development of water transportation. 



16. Sinking and floating bodies are buoyed up by a force 

 equal to the weight of . 



17. developed the first steamship. 



18. Write a paragraph on the advantages and disadvan- 

 tages of waterways as means of transportation. 



19. Passenger ships are built high out of the water and 

 slim, while freighters are built close to the water and broad. 

 Explain. 



20. The compass may be used to point direction be- 

 cause the is a large and has of force about 



it. 



21. The magnetic compass does not point true north be- 

 cause the poles of the are not at the poles. 



