Circular motion is the movement of an object along the circumference of a circle or a circular path. We can see this in many everyday examples like the Earth orbiting the Sun, a car turning around a curve, or a ball swinging on a string. In this animation, we see an object moving in a perfect circle, with its velocity always pointing tangent to the circular path.
There are two main types of circular motion. Uniform circular motion occurs when an object moves at constant speed around a circle, with only the direction of velocity changing. Non-uniform circular motion happens when both the speed and direction change as the object moves around the circle. Notice how the velocity vectors have different lengths in non-uniform motion, indicating changing speed.
Several key quantities describe circular motion. The radius is the distance from the center to the moving object. The period is the time needed for one complete revolution around the circle. Frequency is how many revolutions occur per unit time. Speed is the distance traveled per unit time along the circular path. These quantities are all related through mathematical formulas.
For an object to move in a circle, it needs a centripetal force that always points toward the center of the circle. This force is what keeps the object from flying off in a straight line. The centripetal force is given by the formula F equals m v squared over r, where m is mass, v is speed, and r is radius. Examples include the tension in a string for a ball on a rope, gravitational force for planetary orbits, or friction for a car turning.
To summarize what we have learned about circular motion: It is the movement of an object along a circular path. It can be uniform with constant speed or non-uniform with changing speed. Key quantities include radius, period, frequency, and speed. Centripetal force directed toward the center is always required. Circular motion is found everywhere in our universe, from electrons orbiting atoms to planets orbiting stars.