iven velocity in a circle of a given
diameter?

_A._--Yes. If the velocity in feet per second be divided by 4.01, the
square of the quotient will be four times the height in feet from which a
body must have fallen to have acquired that velocity. Divide this quadruple
height by the diameter of the circle, and the quotient is the centrifugal
force in terms of the weight of the body, so that, multiplying the quotient
by the actual weight of the body, we have the centrifugal force in pounds
or tons. Another rule is to multiply the square of the number of
revolutions per minute by the diameter of the circle in feet, and to divide
the product by 5,870. The quotient is the centrifugal force in terms of the
weight of the body.

27. _Q._--How do you find the velocity of the body when its centrifugal
force and the diameter of the circle in which it moves are given?

_A._--Multiply the centrifugal force in terms of the weight of the body by
the diameter of the circle in feet, and multiply the square root of the
product by 4.01; the result will be the velocity of the body in feet per
second.

28. _Q._--Will you illustrate this by finding the velocity at which the
cast iron rim of a fly-wheel 10 feet in diameter would burst asunder by its
centrifugal force?

_A._--If we take the tensile strength of cast iron at 15,000 lbs. per
square inch, a fly-wheel rim of one square inch of sectional area would
sustain 30,000 lbs. If we suppose one half of the rim to be so fixed to the
shaft as to be incapable of detachment, then the centrifugal force of the
other half of the rim at the moment of rupture must be equal to 30,000 lbs.
Now 30,000 lbs. divided by 49.48 (the weight of the half rim) is equal to
606.3, which is the centrifugal force in terms of the weight. Then by the
rule given in the last answer 606.3 x 10 = 6063, the square root of which
is 78 nearly, and 78 x 4.01 = 312.78, the velocity of the rim in feet per
second at the moment of rupture.

29. _Q._--What is the greatest velocity at which it is safe to drive a cast
iron fly-wheel?

_A._--If we take 2,000 lbs. as the utmost strain per square inch to which
cast iron can be permanently subjected with safety; then, by a similar
process to that just explained, we have 4,000 lbs./49.48 = 80.8 which
multiplied by 10 = 808, the square root of which is 28.4, and 28.4 x 4.01 =
113.884, the velocity of the rim in feet per second, which may be
considered as the highest consistent with