In the S.I. system, the correct unit for moment (torque) is the newton–metre. Choose the proper expression for moment and avoid mass–length units which are not S.I. for torque.

Introduction:
Moment (torque) quantifies the rotational effect of a force about a pivot. It is central to statics, machine design, and structural analysis. Using the correct S.I. unit prevents dimensional errors when applying equilibrium equations or sizing components like shafts and bolts.

Given Data / Assumptions:

• Force is measured in newtons (N).
• Lever arm (perpendicular distance) is measured in metres (m).
• Moment is defined as force * perpendicular distance.

Concept / Approach:

By definition, moment M = F * d. In S.I., F is in N and d is in m, so M is in Nm. Units like kgm correspond to mass–length, not force–length, and therefore are not correct for torque.

Step-by-Step Solution:

Verification / Alternative check:

Dimensionally, N = kgm/s^2, so Nm = kgm^2/s^2, which is consistent for torque. Pressure (Pa), energy-time (Js), or power (W) do not match this dimension for pure torque.

Why Other Options Are Wrong:

• kgm: Missing acceleration; not force–length.
• Pa: Unit of pressure (N/m^2).
• Js: Action or angular momentum-like dimension; not torque.
• W: Power (J/s), not torque.

Common Pitfalls:

• Using kgm out of habit from weight-based systems (kgfm); correct S.I. uses Nm.
• Confusing torque (Nm) with energy (also Nm numerically) but representing different physical quantities.

Final Answer:

Nm