Torque measures the amount of force that is applied to a rotating shaft; it is the force that causes the shaft to rotate. It is measured in foot-pounds (ft-lb) or Newton-meters (N-m). One foot-pound is equivalent to the force required to lift a one-pound weight one foot off the ground.
The relationship between horsepower and torque is:
```
Horsepower = (Torque × RPM) / 5252
```
where:
* Horsepower is measured in horsepower (hp)
* Torque is measured in foot-pounds (ft-lb)
* RPM is the rotational speed of the shaft in revolutions per minute (rpm)
So, if you know the torque and RPM of a shaft, you can calculate the horsepower.
Example:
A shaft is rotating at 1,000 rpm and has a torque of 100 ft-lb. What is the horsepower of the shaft?
```
Horsepower = (100 ft-lb × 1,000 rpm) / 5252
= 19.04 hp
```
So, the shaft is producing 19.04 horsepower.
In general, a high-horsepower engine is needed for tasks that require a lot of power to be produced quickly, such as accelerating a car. A high-torque engine is needed for tasks that require a lot of force to be applied over a long period of time, such as pulling a heavy load.