Fluid Pressure 



87 



pressure on the bottom ; and the difference between 

 them is equal to the weight of the water displaced. 



Exercise for Student. 



Show that the last statement is true in the case of a cube 

 displacing 1000 c.c. whose top surface is 10 cm. below the surface 

 of the water. Calculate first the weight of water supported by the 

 top surface; then, from (a) above, deduce the upward pressure on 

 the bottom surface. 



51. A further and very important point concerning 

 the nature of fluid pressure is that it is exerted equally 

 in all directions. It is not an easy matter to arrange 



A 



Fig. 26. 



a simple experiment whereby this equality of pressure 

 may be shown by actual measurement, but reference 

 may be made to well-known facts in support of this 

 idea. Thus we know that, if a rubber ball be squeezed 

 between the thumb and forefinger, the tvhole of the 

 exterior surface of the ball becomes harder to the touch. 

 Compressing the ball at two points has decreased 

 the volume, and hence increased the pressure, of the 

 air within the ball. The new pressure, instead of being 

 exerted only at the points of squeezing, is distributed 

 evenly over the entire surface of the ball. An applica- 

 tion of this principle is afforded by the hydraulic press, 



