The principle of superposition

What happens when several forces act upon an object? In this case, the action of all the forces acting on a system can be replaced with a single force that produces the same results – this force is called the net force.

The net force is equal to the vector sum of all the forces acting on the object:
\[\mathbf{F}_{\mathrm{net}} = \sum{\mathbf{F}}\]

Newton's second law extended for several forces:

\[\sum{\mathbf{F}} = m \mathbf{a}\]

A useful corollary of this observation is that any force can be replaced by the action of two forces provided their vector sum is equal to the original force.

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