From Mechanics

Newton's First Law

A particle will move with a constant velocity or remain at rest if the resultant force on the particle is zero.

Equilibrium

If the resultant force on a particle is zero, then the forces acting on the particle are said to be in equilibrium.

The Universal Law of Gravitation

\displaystyle F=\frac{Gm_{1}m_{2}}{d^{2}}

\displaystyle G=6.67\times 10^{-11}\text{ kg}^{\text{-1}}\text{m}^{\text{3}}\text{s}^{\text{-2}}

Gravity on Earth

The force of gravity is often called the weight.

\displaystyle \begin{align} & F=mg \\ & g=9.8\text{ ms}^{\text{-2}} \\ \end{align}

Data

Radius of Earth is \displaystyle \text{6}.\text{37}\times \text{1}0^{\text{6}}\text{ } metres

Mass of Earth is \displaystyle \text{5}.\text{98}\times \text{1}0^{\text{24}}\text{ } kg