The Absolute Unit of Force
المؤلف:
ESSENTIALS OF PHYSICS
المصدر:
GEORGE A. HOADLEY
الجزء والصفحة:
p-47
2025-10-23
25
in the C. G. S. system, is the dyne. This is the force that, acting upon 1 g. of mass, will give to it an acceleration of 1 cm. per second per second.
Since the dyne is a very small unit, it is sometimes convenient to use, instead, the megadyne, equal to 1,000,000 dynes.
In the F. P. S. system, the absolute unit of force is the poundal, which is the force that by pushing against 1 lb. of matter will give to it an acceleration of 1 ft. per second per second.
The formula F = Ma refers to absolute units; it means
•For instance, to measure a force that gives to a mass of 6 g. an acceleration of 5 cm. per second per second, we write F = Ma = 6× 5 = 30 dynes.
Again, to determine the weight of a 1-pound mass at New York, or the force by which a mass of 1 pound is pulled downward by gravity there, we observe that a freely falling body at New York has an acceleration of 980.2 cm. or 32.16 ft. per second per second.
Hence in this case F = 1 × 32.16 = 32.16 poundals.
Since the dyne gives to one gram of matter an acceleration of 1 cm. per second per second and gravity acting on this same gram gives it an acceleration of 980.2 cm., the weight of 1 gram = 980.2 dynes. The force of gravity varies a little at different points on the earth's surface. But if we let g represent the acceleration due to gravity, and W the weight expressed in absolute units of force, the formula will hold true for any place whatever.
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