Newton's First Law
The principle that an object remains at rest or continues in uniform motion in a straight line unless acted upon by a net external force.
Governing formula
∑ F = 0 ⇒ v = constant
SI unit
N/A
In depth
Also known as the Law of Inertia, this law defines inertial reference frames - frames where non-accelerating motion requires no sustaining force.
Examples in the real world
A hockey puck gliding almost endlessly across smooth ice, or passengers lunging forward when a bus brakes suddenly.