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An object travels in uniform circular motion, so its speed never changes. Why does it still have an acceleration?
AAcceleration also occurs whenever the direction of velocity changes
BAcceleration only exists when speed itself is changing
CUniform circular motion has zero acceleration by definition
DThe object accelerates only at the very start of the motion
Answer & Solution
Correct answer: A. Acceleration also occurs whenever the direction of velocity changes
1. Acceleration is defined as a change in velocity, and velocity changes if either its magnitude or its direction changes.
2. In uniform circular motion the speed, which is the magnitude of velocity, stays constant, but the direction of velocity changes constantly as the object turns.
3. That continuous change in direction is itself a change in velocity, so an acceleration is present even though speed never changes.
4. Saying uniform circular motion has zero acceleration, or that acceleration only comes from a changing speed, ignores the direction part of velocity entirely.
_Source: OpenStax College Physics (CC BY 4.0), Ch 6 "Uniform Circular Motion and Gravitation", section 6.2 Centripetal Acceleration_
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