For example : A body moving with constant speed in a circular motion do not have constant (or uniform) velocity because the velocity changes its direction continuously.

As a bucket of water is tied to a string and spun in a circle, the tension force acting upon the bucket provides the centripetal force required for circular motion. As the moon orbits the Earth, the force of gravity acting upon the moon provides the centripetal force required for circular motion.

The direction changes due to the centripetal acceleration which is radially inward. Thus, the net acceleration in the case of uniform circular motion is perpendicular to the velocity. (a) The acceleration of the particle is zero. (b) The rate of change of speed equals the magnitude of the rate of change of velocity.

It is useful to think of the motion as starting from rest at the maximum position and accelerating downward along the curve. The tangential acceleration is greatest when position is maximum and zero at the low point.

The tangential component is the part of the acceleration that is tangential to the curve and the normal component is the part of the acceleration that is normal (or orthogonal) to the curve.

An object can move in a circle and not have any tangential acceleration. No tangential acceleration simply means the angular acceleration of the object is zero and the object is moving with a constant angular velocity.

What is the difference between constant speed and variable speed? Constant speed does not change and variable does change. Roller coasters, bikes, and cars are objects that travel at variable speeds.