To find this quantity on a loop of wire,  start with the product of current times vector area, and cross that with the external magnetic field.  
A converter named for this concept is in cars with automatic transmissions instead of a clutch,   allowing drivers to use the brakes without harming the car. To find this quantity on a loop of wire,  start with the product of current times vector area, and cross that with the external magnetic field.   Work can be found by integrating this quantity with respect to angle, and this quantity is equal to  the time derivative of angular momentum. Name this quantity equal to both moment of inertia times  angular acceleration and to position vector cross force, the rotational analogue of force.
A converter named for this concept is in cars with automatic transmissions instead of a clutch,   allowing drivers to use the brakes without harming the car.
torque