Units for moment (moment of force) in the MKS gravitational system: What is the conventional unit for a moment in the MKS gravitational system?

Introduction / Context:
The unit of a moment (moment of force) depends on the force unit used. In the SI coherent system, moment is expressed in newton–metre (N·m). In the older MKS gravitational system commonly used in many basic mechanics texts, force was expressed in kilogram-force (kgf), leading to the moment unit kgf·m, often abbreviated as kgm.

Given Data / Assumptions:

• Gravitational MKS uses kilogram-force (kgf) as the force unit.
• Moment = Force * Distance (perpendicular).
• Distance measured in metres.

Concept / Approach:
Dimensionally, a moment is the product of a force and a length. Thus, in gravitational MKS: moment unit = kgf * m (written as kgm in many problems). In SI: 1 kgf ≈ 9.80665 N, so kgf·m can be converted to N·m when needed.

Step-by-Step Solution:

Verification / Alternative check:
In SI, replace kgf by newton: 1 kgf·m ≈ 9.80665 N·m. The structure “force × length” remains the same across systems.

Why Other Options Are Wrong:

• kg/m^2, kg/s^2, kg/s: not “force × length”.
• N·m^2: contains an extra metre; the standard SI unit is N·m.

Common Pitfalls:
Confusing mass with force; forgetting the “perpendicular distance” notion does not change the unit—still force times length.

Final Answer:
kgm