FLUID FORCES. 



: To sum up : 



If the piston of a hydraulic press is to lift 

 a weight in some definite proportion to the 

 pressure applied at a force-pump handle, the 

 area of the lifting cylinder, multiplied by the 

 leverage, must have the same proportion to 

 the area of the force-pump barrel. 



2. Fluids defying Gravity. 



Let a tumbler be filled with water and 

 covered with a piece of light cardboard or 

 stiff paper. While the paper is held lightly in 

 position, let the tumbler be inverted, and the 

 support then withdrawn from the paper, as in 

 Fig. 21, A. It will remain in position, and 

 the water will not fall out of the tumbler 

 while the latter is held up without any support 

 underneath it. 



The explanation is that gases, like liquids, 

 are fluids, and transmit pressure equally in 

 all directions. The air, then, transmits in all 

 directions the pressure due to its own weight, 

 and it thus presses upwards beneath the under 

 surface of the card with a force of nearly 15 

 Ib. to the square inch, forcing the card against 

 the water. But the column of water on the 

 upper surface of the card, inside the tumbler, 

 if the tumbler be of ordinary height, weighs 

 only about 2 oz. to the square inch, so that 

 the air underneath presses the card upwards 



85 



