Poundal
Encyclopedia : P : PO : POU : Poundal
The poundal is a non-SI unit of force. It is a part of the absolute foot-pound-second system of units, a coherent subsystem of English units introduced in 1879, and one of several specialized subsystems of mechanical units used as aids in calculations. It is defined as 1 lb·ft·s-2, or in words, as the force necessary to accelerate a pound of mass at 1 foot per second, per second.
English units require either re-scaling of either force or mass to eliminate a numerical proportionality constant in the equation [F = ma]. The poundal represents one choice, which is to rescale units of force. Since a pound of force accelerates a pound of mass at about 32 ft/s² (the acceleration of gravity = g), the smaller unit of force represented by the poundal is chosen as that force which accelerates a 1-pound mass at 1 foot per second^2. The poundal is only about 1/32 of a pound of force.
The poundal-force, pound-mass system is contrasted with an alternate system in which pounds are used as force, and instead, the mass unit is rescaled by a factor of 32. If force is given in pounds rather than poundals, then an acceleration of one foot per second^2 is induced in a mass of about 32 pounds mass, for each applied pound of force. The mass unit of about 32 mass-pounds (32.2 to three digits) in this alternate system, is called a slug.
Note that slugs and poundals are never used in the same system, since each exists to solve the same problem, so that both should not be used together.
1 pdl = 0.138 254 954 376 newton (N) exactly
| Newton (SI unit) | Dyne | Kilogram-force (Kilopond) | Pound-force | Poundal | |
| 1 N | = 1 kg·m/s² | = 105 dyn | ≈ 0.10197 kp | ≈ 0.22481 lbf | ≈ 7.2330 pdl |
| 1 dyn | = 10−5 N | = 1 g·cm/s² | f | ||
| 1 kp | = 9.80665 N | = 980665 dyn | Acceleration due to gravity>gn·(1 kg) | ≈ 2.2046 lbf | ≈ 70.932 pdl |
| 1 lbf | ≈ 4.448222 N | ≈ 444822 dyn | ≈ 0.45359 kp | gn·(1 Pound (mass)>lb) | ≈ 32.174 pdl |
| 1 pdl | ≈ 0.138255 N | ≈ 13825 dyn | ≈ 0.014098 kp | ≈ 0.031081 lbf | ft/s² |
| The value of gn as used in the official definition of the kilogram-force is used here for all gravitational units. | |||||
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