Convert poundal to megadyne

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.

The centimetre-gram-second system preceded the SI and its units linger in physics: the dyne is the force that accelerates one gram at 1 cm/s² (10⁻⁵ N), and the erg the work of one dyne over one centimetre (10⁻⁷ J), about the energy of a mosquito's wing beat. Astrophysics still writes luminosities in erg/s (the Sun: 3.8 × 10³³ erg/s), and surface tension is often quoted in dyn/cm, which equals mN/m.

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.