Answer::
Literally, force means the push or pull of a body. By pulling or pushing a body, the overall pressure of the body will be increased; if the body is in motion, it's direction might be changed; in fact, force can cause the body to change its shape from one form to another.
So, at this point we can define force as an interaction that (1) alters the state of rest or uniform motion of a body (2) alters the direction or shape of an body. (3) causes a body to accelerate.
Force is a vector quantity; meaning that it has magnitude and direction.
Force is measured by multiplying the mass of the object by its accelerate;
Mathematically, Force (F) = Mass (m) * Acceleration (a)
F = m * a
F = ma
Mass is measured in kilogram (kg) and acceleration is measured in metre per square second (m/s²)
We use the above to derive the unit of force
F = kg * m/s²
F = kgm/s² --- this is equivalent to 1 Newton (N)
So, force is measured in kgm/s² or more appropriately, Newton
The SI units of force is Newton (N)
Example:
The force that cause a body of mass 5kg to move at an acceleration of 6m/s² is
Force = mass * acceleration
Where mass = 5kg
Acceleration = 6m/s²
Force = 5kg * 6m/s²
Force = 30kgm/s²
Force = 30N