The gravitational force between two masses is modeled using the following function:

$F_g(r)=G\frac{m_1{m}_2}{r^2}$

where $F_g=$ gravitational force $($Newtons$)$

$G=6\mathrm{.}673{10}^{-11}\frac{(N)*m^2}{k{g}^2}$

$m_1=$ mass number $1(kilograms)$

$m_2=$ mass number $2(kilograms)$

$r=$ distance between centers $of$ masses $(meters)$

Which type of mathematical model is used here to describe the gravitational force?

Linear model

Nonlinear model

Exponential model

Trigonometric model