The dual use of the imperial and metric systems is more complicated than simply converting inches to centimeters or pounds to kilograms. It affects many scientific calculations that involve forces and distances. The newton meter and foot-pound are the metric and imperial measures for torque, which measures the way in which a force turns an object around an axis.
Definitions of Terms
A newton meter is the torque produced by a force of one newton being applied to a one meter-long moment arm, which is most easily envisioned as a spoke coming out of a central hub, such as the connection to a seat on a playground carousel. A foot-pound is the torque produced by a one-pound force being applied to a one-foot long moment arm. A one-pound force is equivalent to the gravitational force the Earth pulls on an object weighing one pound that is on the Earth's surface; a newton is the same thing but with an object weighing around 102 grams.
Conversions of Units
The conversion rate between newton meter and foot-pound is a combination of the ratios of feet to meters and pounds to newtons. The result is that one newton meter equals 0.738 foot-pounds. Stated the other way, one foot-pound equals 1.356 newton meters.
Both the terms "newton meter" and "foot-pound" can refer to energy rather than torque. To avoid such confusion, scientists following the SI system only use "newton meter" to refer to torque and instead use "joules" for energy. Some people use "pound-foot" when referring to torque and "foot-pound" when referring to energy, but this usage isn't universal.
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