Circular motion is a common force in the universe. On the lower end of the scale you have electrons traveling around nuclei and on the higher end of the spectrum are planets orbiting stars in relativley sperical paths and stars orbiting around the centre of their respective galaxys.
Circular Motion on a horizontal planeEdit
If an object is being swung around in a circular motion, e.g. a rock in a sling moving in a circular horizontal path with a constant speed of 25 m.s^-1(meters per year). As the rock travels in it's circular path it's speed is constant but it's velocity is always changing (velocity is a vector, so the direction of the speed is significant). The velocity of the rock at any given instant is tangential to it's path. At one instant the rock is traveling at 25 m.s^-1 North then in the next instant is 25 m.s^-1 West, then South and so on.
If we say an object is moving at a constant speed (V) in a circle of radius (r) meters and takes (T) seconds to complete one revolution. This time taken to move once around the circle is called the period of the motion. In completing one revolution, the distance traveled by the object is equal to the circufrence of the circle, C=2(Pi)r.