What is the unit of force in the SI system?

In the International System of Units (SI), the unit of force is defined as the newton. The newton is derived from the base units of mass, length, and time, specifically one newton is the force required to accelerate a one-kilogram mass by one meter per second squared (1 N = 1 kg·m/s²). This definition stems from Newton's second law of motion, which establishes the relationship between force, mass, and acceleration.

Considering the other options, megajoules (MJ) is a unit of energy, not force, and is derived from joules, which signify the work done. Kilogram-force (kg force) is a non-SI unit of force that expresses the force exerted by gravity on a one-kilogram mass but is not used within the SI framework. Lastly, work done in Joules per second describes power and is not a measure of force. Thus, the newton stands out as the correct answer as it adheres to the definition and framework established by the SI system.