Up: Glassmaking
Gilbert: 22 of 65
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Experiment 13. Magic.
Place the pollywog in a bottle filled to
overflowing with water, insert the solid rubber stopper, and
press it down hard. Does the pollywog sink?
FIG. 26
ACROBATS
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Now release the stopper quickly. Does
the pollywog turn somersaults in a most magical manner (1, Fig.
26), and also rise?
Make one or two more pollywogs, place
them all in the bottle together (2, Fig. 26), and entertain your
friends with a pollywog circus.
The pollywog sinks when you press down on
the stopper because you compress the air in it and force water in
until it weighs more than the water it displaces.
The pollywog rises when
FIG. 27
DANCING POLLYWOGS
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you release the
stopper because the compressed air drives the water out until
the pollywog weights less than the water it displaces.
The pollywog turns a somersault because
the water rushes out sidewise in one direction and forces the
nozzle in the other direction.
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