Convert poundal to pound-force

Engineers working in feet and pounds need a mass unit and a force unit that fit Newton's law without a factor of g. The slug is the mass that one pound-force accelerates at 1 ft/s², 32.174 lb or 14.59 kg, and is used with the pound-force in US aerospace and mechanics. The poundal goes the other way: it is the force that accelerates one pound at 1 ft/s², 0.1383 N, and is now rarely met outside old textbooks.

Scales are marked in kilograms, but the kilogram measures mass, and weight is the force gravity exerts on that mass. The kilopond (kp, also written kgf) is the weight of one kilogram under standard gravity, 9.80665 N; it was a legal unit in Germany until 1978 and survives in older manuals. The pound-force (lbf) is the same idea for the pound, 4.448 N, and is still the everyday force unit in US engineering. The newton is the SI unit: a 100 g apple weighs about 1 N.

A newton is roughly the weight of an apple, of 102 g to be exact. Before the SI, force was measured in kilograms-force or kiloponds (kp), the weight of a kilogram, 9.81 N; old German torque figures in 'mkp' and towing limits in kp come from that era, and the pound-force (4.45 N) plays the same role in the US. The decanewton, 10 N, is popular in France, Italy and on lashing straps and slings precisely because it is almost a kilogram-force (1.02 kp), so 'LC 2500 daN' on a strap means about 2.5 tonnes. Climbing gear is rated in kilonewtons: a 22 kN karabiner holds about 2.2 t.