Uniform Circular Motion - Key Concepts

An object in uniform circular motion travels at a constant speed along a circular path.
Even though the speed is constant, the direction of the object's velocity is continuously changing, which means the object is accelerating.
This acceleration, known as centripetal acceleration, always points towards the center of the circle.

When an object's speed changes during circular motion, it experiences an additional acceleration called tangential acceleration. This acts along the direction of motion, either speeding up or slowing down the object.
The radial (centripetal) acceleration is still present and always points towards the center of the circle.
The total acceleration for non-uniform circular motion is a combination of both tangential and radial accelerations.
If the speed is constant, there is no tangential acceleration, and only radial acceleration exists.

Centripetal acceleration is greater with higher speeds and for tighter turns (smaller radius).
At certain points, such as the top or bottom of a loop, the tangential acceleration might be zero for an instant, meaning the total acceleration is solely radial and points towards the center.

At Point A: The object moves upward and slows. Tangential acceleration opposes the motion, while radial acceleration points towards the center (left). Total acceleration is their vector sum.
At Point B: The object moves downward and speeds up. Tangential acceleration is downward (with motion), and radial acceleration points towards the center (right). The direction of total acceleration depends on their relative strengths.
At Point D (top): There is no instantaneous tangential acceleration. The total acceleration is purely radial, pointing downward toward the center.