68 ELEMENTS OF LABORATORY WORK 



stress (or force), we must pay regard both to the rate of change 

 of speed and also to the quantity of matter in which it is 

 produced. 



Additional Exercises and Questions. 



1. Why does water remain in a pipette when the upper end is closed ? 



2. Draw a diagram to explain how the reading of a barometer will 

 be affected by a divergence of the instrument from the perpendicular. 



3. Observe the level of the liquid in the various 

 branches of the vessel shown in fig. 21. How do your 

 observations explain the relation of pressure to dis- 

 tance from surface ? 



4. What would be the pressure on that is, what 

 would be the quantity of matter supported by a sheet 

 of 1 square centimetre area placed at a depth of 1 



Fig. 21. metre in water ? What is the pressure when it is 



placed in mercury ? Why does the sheet not move 

 downwards under this pressure, and how is that quantity of matter 

 supported ? It is assumed that the liquid is over 1 metre in depth. 



5. Explain why a body immersed in a liquid is partially or com- 

 pletely supported by the liquid. To what extent is the body supported, 

 and why does it depend on the volume ? 



6. When a solid floats on a liquid, what will determine how much is 

 submerged below the surface of the liquid ? 



7. Observe and explain what takes place when a liquid (water, for 

 example) in a beaker, and a solid with a piece of silk attached, are 

 weighed when lying side by side in the pan of a balance ; and also when 

 the solid is suspended by the silk from the hook at the end of the beam 

 and immersed in the water. Also observe and explain what takes place 

 when a beaker of water is weighed, and then a solid hanging from an 

 independent support is placed in the liquid. Prove that what the water 

 appears to gain in this case is exactly the same as the object appears to 

 lose if it is made to hang from the beam, while the water is supported 

 independently, as in determining density. 



8. Fill with water a tube which has been closed at one end, and is 

 about a metre long, place the thumb over the end, and remove the thumb 

 when the open end is underneath the surface of water in another vessel. 

 Observe that the water remains in the tube when it is placed upright. 

 Fill a similar tube with mercury and invert it over mercury, and observe 

 that the whole column of mercury in the tube is not supported but 

 sinks to a certain level. Observe also what occurs when the tube is not 

 completely filled with the water or mercury, and likewise the alteration 



