Motion that repeat itself is called periodic motion. A projectile motion, since it doesn't repeat, is not periodic. The motion of a swinging ball is an example of circular motion. Let's analyze the circular motion.

Consider a planet around the Sun.

When there is no external force, an object will travel in a straight line (Newton's First Law of Motion). In order for an object to travel in a circle, there has to be a force that makes it travel in a circle.

When the centripetal force is too strong, the ball will accelerate toward the center of the circle. When the centripetal force is too weak, the ball will get out of the orbit. An object will maintain a circular motion only when the centripetal force is well balanced.

These formulas can be used to calculate the centripetal force:

Where:

Too complicated? Let's see a concrete example.

You are rotating with Earth, so you are experiencing a circular motion.

Say you have a mass of 50 kg. We know the radius of the circle (6,378,000 m = radius of Earth) and its period (24 hours = 86400 seconds). From this information, you can calculate velocity, acceleration, and centripetal force acting on you.

m/s = 1670 km/h.

To calculate acceleration, use the formula .

m/s².