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# Why does an object in uniform circular motion exhibits acceleration when its speed is constant?

Updated: 8/9/2023 Wiki User

9y ago

Acceleration is defined as the change in velocity divided by the time or

a = (vf - vi)/t

Velocity measures the speed and the direction of an object.

In uniform circular motion, the object has the same speed but it is always changing direction and so, by the definition of acceleration, the object is considered accelerating. If this acceleration doesn't exist, the object would move in a straight line according to Newton's laws of motion. Wiki User

12y ago   Wiki User

13y ago

Acceleration involves a change in velocity. In the case you mention, the speed doesn't change, but the velocity does. The term "velocity" includes the direction of the movement, and the direction does change.   Wiki User

10y ago

The reason is that acceleration is defined as the change in velocity per unit time. Velocity is a vector, it points in the direction of motion. Speed on the other hand is just the length of the velocity vector, which remains constant in circular motion (unless the strength of the centripetal force is allowed to vary).

Velocity is not constant, after all the direction of motion in circular motion constantly changes! Therefore there is an acceleration; the direction of the velocity changes (which is thus a change in velocity).   Wiki User

9y ago

Because "acceleration" doesn't mean 'speeding up'. It means any change in

the speed or direction of motion.

The only motion that's not accelerated is motion at a constant speed in a

straight line. If the speed is increasing, or the speed is decreasing, or the

direction is changing, that's acceleration.   Wiki User

14y ago

Velocity is a vector quantity, meaning it has a size and a direction.
The size is what we call "speed".
But a change in direction only is still a change in the velocity.
Any change in velocity ... even if only a change in direction ... is called "acceleration".   Earn +20 pts  