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Questions and Answers for the Certified Horologist

From American Horologist magazine, April, 1936

Questions and Answers for the Certified Horologist

Question No. 1 - Define the terms-acceleration, absolute unit of force, moment of force, center of oscillation, coefficient of expansion, harmonic motion.

Answer - Acceleration is the rate of change of velocity of a moving body, i.e., if the motion of a body is increasing, "acceleration"-the velocity gained per second.

Absolute Unit of Force - That force which, acting on a mass of 1-lb. for one second, gives to that mass a velocity of one-foot-per-second.

Moment - of a force is the tendency of that force to produce rotation, it equals the force times its "leverage." 

Center of Oscillation - That point in a pendulum where, if all its mass were collected, its time of vibration would be unaltered.

Coefficient of Expansion - A number representing the change per unit in the dimensions of a body submitted to the unit change of temperature; or, more directly, the increase per unit in the length of a body when the temperature is raised one degree.

Harmonic Motion is a periodic to and from motion such as that taken by the prongs of a tuning fork, or the motion of a very long pendulum describing very small arcs; the condition of "pure harmonic motion" being that the time occupied shall be independent of any variation in the extent of the path described, i.e., "isochronous motion." 

Note - If a ball were set rolling at a uniform rate in a plane circle, on saying a horizontal table, and its motion observed from a very long distance with one's eye on the same level, it would appear to move, not in a circle, but in a straight line from left to right and from right to left; its velocity as it approaches the center, where it would be at a maximum, and decreasing as it receded from the center, till it reached the extent of its apparent path, where its apparent motion would be 0. 

The motion that such a body would appear to take would be a "pure harmonic motion."

Question No. 2 - A weight of 100 lbs. 
drives a clock and falls through a distance of 60 feet in 8 days. What is the "force" exerted by the weight? Does it sensibly vary during the fall? To what is its force due? What is the energy stored up in the weight when wound to the top? How many foot-pounds of "work" does it do in one day?

Answer - The force exerted by the weight would be 100 lbs.

No. It would not sensibly vary.

The force is due to the "attraction of gravity." 

Its energy = 100 X 60 = 6,000 footpounds.

Work per day = 6000 / 8 =750 foot lbs.

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