What is the unit of force in the SI system?

The unit of force in the SI system is the Newton (N). The Newton is defined as the force required to accelerate a one-kilogram mass by one meter per second squared. This relationship is summarized by Newton's second law of motion, which states that force equals mass times acceleration (F = ma). The Newton is a derived unit that measures how much force is applied to cause a change in motion, and its significance lies in its foundational role in physics, particularly in mechanics.

The other options represent different physical quantities: the pound is a unit of force used in the Imperial system, the joule is a unit of energy, and the pascal is a unit of pressure (which is force per unit area). Understanding the distinction between these units helps clarify the specific role each one plays in the study of physical phenomena.