CENTRIFUGAL FORCE.
That power which drives a revolving body from a centre, and it may be
illustrated by turning a closed parasol, or umbrella, rapidly round on
its centre, the stick being the axis--the ribs fly out, and if there is
much friction in the parts, the illustration is more certain by
attaching a bullet to the end of each rib, as shown in our drawing.
[Illustration: Fig. 21.]
[Illustration: Fig. 22.]
The same fact may be illustrated by a square mahogany rod, say one inch
square and three feet long, with two flaps eighteen inches in length,
hanging by hinges, and parallel to the sides of the centre rod, which
immediately fly out on the rotation of the long centre piece.
The toy called the centrifugal railway is also a very pretty
illustration of the same fact. A glass of water, or a coin, may be
placed in the little carriage, and although it must be twice hanging
perpendicular in a line with the earth, the carriage does not tumble
away from its appointed track, and the centrifugal force binds it firmly
to the interior of the circle round which it revolves.
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[Illustration: Fig. 23.]
Another striking and very simple illustration is to suspend a
hemispherical cup by three cords, and having twisted them, by turning
round the cup, it may be filled with water, and directly the hand is
withdrawn, the torsion of the cord causes the cup to rotate, and the
water describes a circle on the floor, flying off at a tangent from the
cup, as may be noticed in the accompanying cut.
[Illustration: Fig. 24.]
A hoop when trundled would tumble on its side if the force of
gravitation was not overcome by the centrifugal force which imparts to
it a motion in the direction of a tangent (_tango_, to touch) to a
circle. The same principle applies to the spinning-top--this toy cannot
be made to stand upon its point until set in rapid motion.
Returning again to the subject of gravitation, we may now consider it in
relation to other and more magnificent examples which we discover by
studying the science of astronomy.
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