Although both torque and energy can be expressed in Newton-meters, torque is not **energy**. Torque is a vector.

### SI Units

The SI unit for torque is the Newton-meter.

### Imperial Units

In Imperial units, the foot-pound is used. What is meant by that is the force of Earth's gravity on a one-pound object.

### Measuring Torque

Measuring static torque in a linear system like a plane steadily rolling down a flat, frictionless runway is easy. Given the length of the radius, the torque can be found directly.

#### In a Rotating System

Now imagine taking off. The thrust of the engines directs the plane into the air. The takeoff point is the pivot.

There are several other factors, but we will ignore them for the present.

How hard the engine needs to push to keep the plane aloft depends on the distance from the pivot point.

In this case, we can pretend we have a Harrier Jump Jet and we are directing the thrust perpendicular to the runway.

The closer to that pivot point, the harder the engines have to work to thrust upwards. As you get farther away, the engines need not push as hard.

**In practice, measuring torque in a rotating system isn't easy.**

### Electronic Torque Sensors

Electronic torque sensors work by direct or indirect measurement.

Direct measurement uses a torque flange to measure strain within the metal of a drive shaft.

Indirect measurement determines torque through measurement of the motor power at the converter.