Newton's Laws of Motion

First Law — Law of Inertia

An object at rest remains at rest, and an object in motion continues in motion at constant velocity, unless acted upon by a net external force.

$$\vec{p} = m\vec{v} = \text{const} \quad \text{when} \quad \vec{F}_{\text{net}} = 0$$

Second Law

The net force on an object equals the rate of change of its momentum:

$$\vec{F} = m\vec{a}$$

For variable mass systems (e.g. rockets), the full form is $\vec{F} = \frac{d(m\vec{v})}{dt}$.

Third Law

For every action there is an equal and opposite reaction:

$$\vec{F}_{AB} = -\vec{F}_{BA}$$

See also: article-general-relativity for the relativistic extension.

The Newtonian causal chain is visualised in object-newtonian-flow.

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