If an object moves with constant speed in a circular path, its velocity is not constant ; only its speed (the magnitude of velocity) is constant.

Quick Scoop

  • Velocity is a vector, so it has both magnitude and direction.
  • In circular motion, the direction of motion keeps changing at every point along the circle.
  • Since direction changes continuously, the velocity changes continuously, even though the speed stays the same.
  • This also means the object has an acceleration toward the center of the circle (centripetal acceleration).

So we say:

  • Speed: constant
  • Velocity: changing (not constant, never zero)

A helpful way to picture it: imagine a car going around a roundabout at a steady speedometer reading; the arrow showing its velocity would keep rotating as the car turns, so the velocity keeps changing even though the number on the speedometer does not.

In exam language:
“If an object moves with constant speed in a circular path, its velocity is continuously changing because its direction changes at every point on the path.”

TL;DR:
Even with constant speed, circular motion means changing direction, so the velocity is not constant; only its magnitude is.

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