90 FIRST YEAR COURSE IN GENERAL SCIENCE 



100 Ib. 



square centimeters, the total upward effect will be a pressure 

 of 900 X 100 grams. 



97. Buoyancy in Liquids. Careful study of the dia- 

 gram (Fig. 38) will show that the horizontal pressures on 

 opposite sides of the submerged block are equal, but 



are acting in opposite directions, 

 1 Ib, so that the block will not tend to 

 move in either direction sidewise. 

 But as the upward pressure upon 

 the bottom of the block is greater 

 than the downward pressure on 

 the top, the block will be buoyed 

 up in the liquid by a force equal 

 to the difference between the up- 

 ward and downward pressures. 

 This is the reason that a body 

 seems to lose weight in water; 

 part of its weight is supported 

 by upward pressure of the 

 liquid. 



98. Capillarity. If water is 

 put into a glass, it is seen to rise 

 a little higher where it touches the 

 glass than elsewhere at the sur- 

 face. If a glass tube is placed 

 upright in water, the water stands 

 higher in the tube than around it. 

 This rise of liquids in tubes, or on 

 the side of a solid placed in the 

 liquid, is called capillarity. It is 

 due to the attraction of the solid 

 for the liquid. 



Capillarity can be shown with all liquids which wet - 

 that is, adhere to a solid. Mercury does not adhere to glass; 

 it will roll off from clean glass and leave no trace. Mercury 



FIG. 40. TRANSMISSION OF 

 PRESSURE 



1. The area of the piston 

 p is 1 sq. in.; what is the 

 pressure exerted upon the sur- 

 face of the water beneath? 

 2. This pressure is transmitted 

 in every direction: what is 

 the pressure in the horizontal 

 tube? 3. In what direction is 

 pressure exerted in the large 

 cylinder? 4. What is the 

 pressure upon each square 

 inch of P? 5. From the 

 weights indicated here, what 

 must be the area of P? 6. If 

 more weights were placed 

 upon p, and it went down 1 

 in., would Prise 1 in.? Why? 



