EXERCISE 52 



IS THE LATERAL PRESSURE IN WATER DIFFERENT FROM THE PRESSURE 



DOWNWARD OR UPWARD? 



Materials. Thin sheet rubber (dentist's rubber) ; a thistle tube ; rubber and glass tubing ; a 

 funnel ; a meter (or yard) stick. 



Directions. Fasten a thin sheet of rubber over the end of a thistle 

 tube or funnel. Prepare an indicator, which consists of a small glass 

 tube bent as shown and tied or wired to a meter (or yard) stick, the 

 tubing containing some ink or colored water. With a long rubber hose 

 connect the thistle tube with the indicator. Lower the thistle tube to a 

 certain marked depth with the rubber facing upward. Watch the change 

 in level of the liquid in the long arm of the indicator tube. What does 

 this change mean ? With the rubber face of the thistle tube at the 

 marked depth take the readings on the indicator. Change the position 

 of the thistle tube so that the rubber faces sidewise, with its center at 

 the same depth as before. Take readings again, and record. Place the 

 thistle tube with the rubber facing downward, its center at the same 

 depth, and again record the readings. What changes, if any, are noted 

 in the level of the liquid in these three different positions ? Upon what 

 does the pressure in water depend ? Would the readings be different if 

 you placed the funnel in a larger jar at the same depth ? Try it. 



Additional problems. Why is a dam built wider at the bottom than at the top ? 

 Does the size of a reservoir govern the pressure ? 



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