PRESSURE IN LIQUIDS 31 



of books you can raise up from the rim of the pan. To what is 

 the pressure due? 



Fig. 16 shows how this principle is used in the 

 hydraulic press. The piston p is small and the cylinder 

 c is many times larger ; if p is pushed downward, water 

 in the pipe transmits its pressure to the lower end of <?, 

 and c is pushed upward with as much greater force than 

 is used at p as the lower surface of c is greater than 

 that of p. Very powerful presses and hydraulic jacks 

 are made in this manner. 



QUESTIONS 



1. What substances are called fluids? Why? What force 

 causes fluids to flow ? Does the same force act upon the particles 

 of solid bodies? Why do they nof flow? 



2. Explain how pressure in liquids is caused. At the same 

 depth in a liquid what is true of pressures in different directions ? 



3. Upon what does the greatness of liquid pressure depend? 

 State the law or principle in regard to this. 



4. What is true of the surface of a liquid at rest ? Explain 

 why this is so. Did you ever see a liquid surface which was not 

 level? What made it so? Was it at rest? 



5. Explain the method of supplying cities with water. Could 

 the reservoir be lower than the city ? How high will water rise 

 in the pipes ? Why does it not rise as high as the surface in the 

 reservoir ? 



6. Show the cause of buoyancy in liquids. Does it act upon 

 all bodies, heavy and light? State anything of this sort that 

 you have experienced. 



7. Give the general law for buoyant force. State the Law of 

 Floating Bodies. Why do steel vessels float? 



8. How is the specific gravity of a liquid most easily found? 

 Cream is made of oily particles. Why does it rise to the top of 

 milk? Why does it not rise more rapidly? 



