Here's why:

* Moment of a force is the tendency of a force to rotate an object around an axis. It's calculated by multiplying the force by the perpendicular distance from the axis of rotation to the line of action of the force.

* Force is measured in Newtons (N).

* Distance is measured in meters (m).

Therefore, the unit of moment of force is the product of these two units: Newton-meter (Nm).