What is the unit of force in the SI system?

The unit of force in the SI system is the newton. The symbol for the newton is N. The newton is what is referred to as a derived unit. Derived units are composed of a combination of the SI fundamental units. There are seven fundamental SI units:

$\hspace{2em}$ metre (m) used for measuring length
$\hspace{2em}$ second (s) used for measuring time
$\hspace{2em}$ kilogram (kg) used for measuring mass
$\hspace{2em}$ kelvin (K) used for measuring temperature
$\hspace{2em}$ ampere (A) used for measuring electric current
$\hspace{2em}$ mol (mol) used for measuring quantities
$\hspace{2em}$ candela (cd) used for measuring luminous intensity

Using our known physics equations, we can determine how to express the newton in fundamental SI units. Starting with Newton’s First Law,

$\hspace{2em}\ F = ma$

We can substitute the units for the variables to get

$\hspace{2em}$ 1 N = (1 kg)(1 m s$^{-2}$)

Therefore the unit kg m s$^{-2}$ is equivalent to N