constantvelocity

Constant velocity refers to a motion state where an object's velocity vector does not change with time. This means both its speed (the magnitude) and its direction remain constant. In an inertial reference frame, constant velocity implies zero acceleration, so there is no net external force acting on the object according to Newton's first and second laws. The path is a straight line at a constant rate of motion.

Constant velocity is distinct from constant speed. An object can move at a constant speed while its direction changes, resulting in a nonzero velocity vector (for example, uniform circular motion).

Velocity is a vector quantity and depends on the observer's frame of reference; constant velocity is defined relative to a chosen inertial frame. If another observer is accelerating, their measurement of the same motion may not be constant, although acceleration remains invariant under Galilean transformation, but the frame-dependent interpretation matters.

Common examples include a car cruising in a straight line at a steady 60 miles per hour or a spacecraft coasting through space with no thrust. In contrast, planets in orbit generally do not have constant velocity because gravity continuously changes direction and speed during their orbit.

Conclusion: constant velocity is a useful idealization for describing straight-line, unaccelerated motion and forms the basis for many introductory analyses in classical mechanics.