Bukhovtsev-et-al-Problems-in-Elementary-Physics

78
PROBLEMS
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Fig. 135 Fig. 136
be done to bring it to the surface. Therefore, each molecule of
the surface layer has excess potential energy equal to this work.
The average force that acts on any molecule from the side of
all the others, however, is always equal to zero if the liquid is
in equilibrium. This is why the work done to move the liquid
from a depth to the surface should also be zero. What is the
origin, in this case, of the surface energy?
358. One end of a glass capillary tube with a radius r = 0.05 cm
is immersed into water to a depth of h:=. 2 ern. What pressure
is required to blow an air bubble out of the lower end of
the tube?
359. A glass capillary tube with an internal diameter of 0.5 mm
is immersed into water. The top end of the tube projects by
2 em above the surface of the water. What is the shape of
the meniscus?
360. Water rises to a height h in a capillary tube lowered
vertically into water to a depth I (Fig. 135). The lower end
of the tube is closed, the tube is then taken out of the water
and opened again. Determine the length of the water column
remaining in the tube.
361. Two capillary tubes of the same cross section are lowered
into a vessel with water (Fig. 136). The water in the straight