# Centrifugal Force vs. Centripetal Force

Centrifugal and Centripetal forces may both be called a force, but one of them is really not a force at all. There is a relationship between the two forces, however. Centrifugal results from inertia, the tendency of an object to resist any change in its state of motion or when it is at rest, though it is technically not a force. Centrifugal describes an object as it flies outward along a curved path, away from the center of the curve. Often times it is called an "apparent force", mainly because it feels like a force.

On the other hand, centripetal force is a true force that will offset the centrifugal "force" stopping the motion of the object from its flying outward, keeping it in motion instead at a consistent speed along the curved or circular path. Centripetal is the force that prevents the moon from floating out of the Earth's orbit.

Centrifugal force was defined in 1659 by Christiaan Hygens, and Isaac Newton defined centripetal force 25 years later in 1684.

A major difference between centrifugal and centripetal force is the direction of each. Centrifugal takes place along the radius of the circle from the center out towards the object. For centripetal, it is the opposite, taking place also along the radius of the circle, but from the object in towards the center. Basically, both are defined by their frame of reference, centrifugal from the center towards the outside, centripetal from the outside towards the inside or center.

A couple examples of each type of force may help one see the difference between the two. A centrifugal force example is the mud flying off of a spinning tire, or children being pushed out on a merry-go-round. The force the children feel is centrifugal force pushing them outward.

A common example for centripetal force is the moon or a manmade satellite orbiting the Earth. The force comes from gravity, and is the same force allowing the planets to orbit the Sun. If an object was being swung around on a rope the centripetal force is the tension in the rope. For a spinning object, the force is provided by internal stress. A car moving along an arc, such as on a racetrack, the centripetal force comes from the friction between the tires on the car and the road. A loop traveled on by a roller coaster is another example of centripetal force.

The formula for centrifugal and centripetal force is the same: F = mac = mv2/r. ac is the centripetal acceleration, m is the mass of the object, moving at velocity (v) along a path with radius of curvature (r).

Understanding and applying centrifugal and centripetal force is useful to many problems in society. One example is related to the design of roads to prevent skidding, and to improve traction on curves and access ramps of highways. The forces also were invaluable for the invention of the centrifuge. The centrifuge is used to separate particles suspended in fluid by spinning the test tubes at high speeds.

Finally, some day centrifugal force may provide artificial gravity for space stations and space ships.

In summary, centrifugal force is more of an apparent force and is not a real force, though it is directly related to centripetal force, which is a real force. The major difference between the two is their direction, which is also related to the frame of reference for each force. An example for centripetal force is gravity which allows the moon to stay in its orbit. There are several examples for centrifugal force, including the force felt by children on a merry-go-round as it spins.