How calculate torque?

Rotational force is usually spoken of as torque. Torque is a term we use to talk about a force that acts on a body to change its rate of rotation. It is the rotational equivalent of force in a linear motion system. A torque can arise from a single offset-applied force (using "inertial force" or "central bearing / pin force" to generate the balanced couple), from multiple applied forces, or when analyzing structures... from the slices of the structure outside the area of consideration. Roughly, it is a "force times a closest distance", even if that distance is to a point not on the structure under consideration. See the below link for formalism. In general, a torque does not produce linear displacement of the thing that is being "torqued", but nets to zero displacement over some length or some time. Technically, torque is the turning effect of a couple while moment of a force is the turning effect due to a single force but they are often interchanged. Torque is a type of force that causes an object to rotate.