# What is the missing force on this Free Body Diagram?

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• Newton's first law states that when viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force.
According to Newton’s first law, since the object is at rest, the net force must be zero. Choose up as positive. So down is negative.
Net force $= 0 = 12 N + 8 N - \overrightarrow{F}$
$\Rightarrow \overrightarrow{F} = 20 N$ downwards.
edited Aug 19, 2014