88 Domestic Science 



a diagrammatic representation of which is shown in 

 Fig. 26. A and B are watertight pistons of different 

 diameters which slide freely in the tubes G and D. 

 The entire space between the under surfaces of the two 

 pistons is filled with water. The weights of the ,two 

 pistons are so arranged that, when no extra load is 

 placed on either piston, the lower surfaces of the pistons 

 are at the same level. If now a weight of 1 Ib. be 

 placed on the top of A, this will cause increased down- 

 ward pressure on the water-surface in contact with it, 

 and, unless a corresponding increase in the upward 

 pressure of the fluid on A is effected, it is found that 

 the piston A will move downwards and B will move 

 upwards. That is to say, a downward pressure below 

 A has been converted into an upward pressure on B. t 

 Weights may now be placed on top of B in order to 

 balance the upward pressure on it. It will be noted, 

 however, that a weight of 1 Ib. is not sufficient to 

 effect a balance, but that a considerably greater weight 

 must be used in order to bring the apparatus to rest. 

 Thus, suppose that the area of the lower surface of A 

 is 10 sq. cm., while that of B is 2000 sq. cm., it is found 

 that a weight of 200 Ibs. must be placed on B to equalise 

 the pressure of 1 Ib. on A. 



Exercise for Student. 



Using the definition of pressure given previously, try to explain 

 why the weight on B must be 200 Ib. 



52. We will next attempt some experiments in 

 which the effect of the upthrust on solid bodies denser 

 than water, when they are immersed in that liquid, is 

 considered. 



EXPERIMENT 28. Obtain two bodies of equal 

 volume, made of different materials, e.g. two cylinders 



