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Explanation of Centrifugal Force is Not Real by Ron Kurtus - Succeed in Understanding Physics. Key words: physical science, inertial, fictitious, pseudo, Law of Inertia, velocity, centripetal, School for Champions. Copyright © Restrictions

Centrifugal Force is Not Real

by Ron Kurtus (revised 16 March 2010)

A centrifugal force is the outward inertial force on an object moving along a curved path. It is not a real force but rather a fictitious or pseudo (false) force caused by inertia on the object. It is also sometimes called the centrifugal effect.

Objects will move on a curved path if a centripetal force, perpendicular to the direction of motion, is applied to the object. The centrifugal force acts in the opposite direction of the centripetal force. They are equal in the amount of force experienced, but the centripetal force is a real force caused by an agent acting on the object, while the centrifugal force is not a real force.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion



Centrifugal is an inertial force

The Law of Inertia or First Law of Motion states that a moving object tends to follow a straight line unless acted upon by some sideways force. That force must be a real force, meaning that it is a push or pull coming from some agent acting on the object.

If that push or pull occurs over a period of time and comes from a center point, the object will follow a curved path. This force is called the centripetal force.

However, inertia "wants" the object to follow a straight line and applies an inertia force on the object, called the centrifugal force. This force is also called a fictitious or pseudo (false) force, since it is not real or created directly from some agent acting on the object. It is also called the centrifugal effect to distinguish it from a force.

Note: One cute way to remember the difference between centripetal and centrifugal is to note that centrifugal is the "f-word" and is thus not a real force.

Examples of centrifugal force

There are various examples of applications of centrifugal inertial force.

Spinning disk

If you place an object on a disk and start it spinning, the friction holding the object on the disk is the centripetal force causing the object to move in a curved path.

Once the disk spins fast enough, the centrifugal inertial force can become greater than the centripetal friction force holding the object in place. The object will then fly off in a straight line.

Ball flies off spinning disk in straight line due to centrifugal force overcoming friction

Ball flies off spinning disk in straight line
due to centrifugal force overcoming friction

Round-Up ride

A related example is the amusement park ride, Round-Up, which consists of a circular platform that has a vertical cage-like wall around the edge.

Centrifugal force holds people on walls in Round Up ride

Centrifugal force holds people on walls in Round Up ride

When the platform spins at a high enough rate, the centrifugal inertial force pushes the riders against the wall, holding them in place as the platform changes directions.

Although the riders feel a force pushing them against the wall, there is no real force or agent that is doing the pushing. It is simply an effect of inertia.

Water stays in swinging bucket

There is also a trick where you take a pail half-full of water and swing it on a rope in a vertical circle, such that the water stays in the bucket, even when directly above you by centrifugal force.

In these examples, you or some object is made to move in a curved path, working against the Law of Inertia.

Amount of centrifugal inertial force

The equation for the centripetal force that causes an object to follow a curved path is:

F = mv2/r

where

This is also the amount of the outward force or centrifugal force caused by inertia on the object.

Centrifugal force is in the opposite direction of centripetal force

Centrifugal force is in the opposite direction
of centripetal force

Thus, if the centripetal force causing an object to go in a circular path is 25 newtons, the centrifugal force felt will be 25 newtons.

Summary

A centrifugal force is the outward inertial force on an object moving along a curved path. It is not a real force but rather a fictitious or pseudo (false) force caused by inertia on the object. Objects move on a curved path if a centripetal force is applied to the object, and centrifugal force acts in the opposite direction of the centripetal force.

The equation for the centrifugal inertial force, as a function of mass, velocity and radius is:

F = mv2/r.


Work beyond your abilities


Resources and references

Ron Kurtus' Credentials

Websites

Physics Resources

Books

Forces In Nature by Liz Sonneborn Rosen; Publishing Group (2004) $25.25 - Understanding gravitational, electrical and magnetic force

The Science of Forces by Steve Parker; Heinemann (2005) $29.29 - Projects with experiments with forces and machines

Glencoe Science: Motion, Forces, and Energy, by McGraw-Hill; Glencoe/McGraw-Hill (2001) $19.32 - Student edition (Hardcover)

Top-rated books on Physics of Force


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