What's the unit of force in the SI system?

The unit of force in the SI system is the Newton (N).

In the International System of Units (SI), the standard unit of force is the Newton, symbolised as 'N'. This unit is named after Sir Isaac Newton, the eminent physicist who made significant contributions to the field of physics, particularly in the area of classical mechanics.

The Newton is defined as the force required to accelerate a one-kilogram mass by one metre per second squared. This is derived from Newton's second law of motion, which states that the force acting on an object is equal to the mass of the object multiplied by its acceleration. In mathematical terms, this is expressed as F = ma, where F is the force, m is the mass, and a is the acceleration.

To give you a practical understanding, one Newton is approximately the force of Earth's gravity on a small apple. This means that if you were to hold an apple in your hand, the force you would feel pulling it downwards is roughly one Newton.

In physics, force is a fundamental concept that describes the push or pull on an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. This force can cause an object with mass to change its velocity, which includes to begin moving from a state of rest, i.e., to accelerate.

In summary, the Newton is the SI unit of force. It is a derived unit, defined in terms of the kilogram (the SI unit of mass), the metre (the SI unit of length), and the second (the SI unit of time). Understanding the Newton and how it is derived is fundamental to the study of physics, particularly when analysing the forces acting on an object and the resulting motion of that object.