**Circular Motion Facts**

Uniform circular motion occurs when anything moves consistently along a circular path. This motion involves a constant acceleration inward toward the center of the circle—this is called centripetal acceleration. So-called centrifugal force is an illusion and therefore has no effect on circular motion. To calculate circular acceleration, divide the square of the moving object’s velocity by the length of the circle’s radius. Circular motion is all around us, from spinning wheels on a car to the movement of the planets. Understanding circular motion and the acceleration involved is key to understanding the physics of the universe.

**Fun Facts**

- While the acceleration of an object in circular motion is toward the center, the object’s velocity is always tangential to the circle.
- Because this velocity is tangential, if a spinning object (like a shot put) is suddenly released from the constraints of circular motion it will continue to travel on that tangent path rather than in a circle.
- “Centrifugal force” does not exist at all, but objects do experience a centrifugal reaction within their reference frame.
- Even though a rotating body may have a constant speed, its velocity is always changing direction and therefore it has an acceleration.
- The smaller the radius of the circle, the more force required to achieve circular motion.
- Similarly, an object with larger mass requires more force to accelerate into circular motion.
- Non-uniform circular motion involves a changing speed and is more complicated to calculate and explain.

**Vocabulary**

- Velocity: The speed of an object with a set direction.
- Acceleration: The rate at which an object’s velocity is changing.
- Tangential: A direction at the edge of a circle which is perpendicular to the radius.

**Questions and Answers**

Question: What kind of force needs to be applied to an object in order to cause it to move in a circular path?

Answer: Centripetal force.

__Learn more__ about circular motion.