In the SI system, the standard unit when indicating force is the:

The standard unit for measuring force in the SI (Système International d'Unités) system is the Newton. The Newton is defined as the amount of force required to accelerate a one-kilogram mass by one meter per second squared. This fundamental definition comes from Isaac Newton's second law of motion, which states that force equals mass times acceleration (F = ma).

The other options represent different physical quantities. Megajoules (MJ) are a unit of energy, not force. Kilogram-force (kg force) is an imperial unit that relates to weight rather than pure force, as it refers to the gravitational force exerted on a mass of one kilogram under standard gravity. Newton-meters (Nm) are a unit of torque, which is a measure of rotational force. These distinctions highlight why the Newton is the recognized and standard force unit within the SI system.