# Force system

Notations and units:

$F$ = Force

Units of the notations are in SI units.

1) Resultant of coplanar and concurrent force system

$R = \sqrt{(\sum F_{x})^{2}+(\sum F_{y})^{2}}$

The angle of resultant from positive x component

$\theta = \tan^{-1}\left ( \frac{\sum F_{y}}{\sum F_{x}} \right )$

2) Resultant of two coplanar and concurrent forces P and Q

$R = \sqrt{P^{2}+Q^{2}+2PQ\cos\theta}$

Angle between resultant and positive x component

$\alpha = \tan^{-1}\left (\frac{Q\sin\theta}{P+Q\cos\theta}\right )$