In the technical specifications of engines and structures equipped with engines, the mysterious nm indicator constantly appears as a unit of torque. If everything is clear with horsepower even at an intuitive level, a horse is a horse, then some difficulties may arise here.
Archimedean lever
The well-known scientist Archimedes once said the famous phrase: "Give me a lever and I will move the Earth." We can say that it was this phrase that served as the beginning of the birth of the torque unit indicator. As you know, the planet Earth is somewhat heavy so that a person, even such a respected and famous one as Archimedes, could turn it over. The key is the use of leverage, which allows you to increase the force of impact on the object by orders of magnitude. A lever is virtually any object that can freely rotate around a fulcrum. If the fulcrum is exactly in the middle of the lever, when applying the same force from each end of the lever, the whole structure will standin place. The situation will change only when the fulcrum shifts to one of the sides. This is best seen in the picture below.
It spins
As you can see, the lever rotates around the fulcrum, making an incomplete revolution. The ratio of the force applied to the long arm of the lever and the force received on the short arm forms the basis of the torque units. The ratio is very simple: the efforts multiplied by the length of the corresponding lever arm must be equal. The law of conservation of energy always works. This principle of operation can be extended to a pair of gears of different diameters, and in general to any aggregates of mechanisms of different diameters interacting by means of rotation, which, in fact, are the arms of conditional levers.
Torque
Now you can take the rotating motor shaft. The radius of the motor shaft is a conditional lever, and when it rotates, a force arises that is directed perpendicular to the axis of rotation. This is shown schematically in the following figure.
Here R is the radius of the shaft, and F is the vector of the force generated during the rotation of the shaft. As with a conventional lever, their product (RF) will be the moment of force, or torque. Since, in accordance with the international system of units, force is measured in newtons, and distance is measured in meters, the unit of torque is the newton meter, or abbreviated as nm.
However, there are other designations. Sometimes to measureforces are used not by newtons, but by kilograms (kgf), then this value can be converted into “classics” using a coefficient. 1 kgf per meter is equal to 9.81 nm. In countries that do not use the metric system, the pound-feet is used as the unit of measure for motor torque. Sounds odd, but still. 1 lb ft is equal to 1.36 nm. There is a relationship between power, speed and torque generated. She is very simple. Power is equal to the product of the frequency of revolutions and torque, divided by a factor. The coefficient depends on the units of torque and other specified values.
If we are talking about horsepower, kgf per meter and revolutions per minute, this coefficient is 716.2, for nm and kilowatts - 9549. The corresponding calculators are available in the public domain. Specifications usually indicate torque measured directly on the motor shaft.
