TheoremProved

Newton's first law (inertia)

Statement

An object remains at rest or in uniform straight-line motion unless acted on by a force, or as long as the net force acting on it is zero.

Why is it true?

This is the operational definition of an 'inertial reference frame' and refutes the ancient idea that a force is needed to sustain motion.

Toggle forces acting on the body and watch its trajectory: with zero net force it keeps uniform straight-line motion (or stays at rest).

Stated by

Topics that use this theorem

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Step-by-step proofs

No step-by-step proof yet for this theorem.

References