Key words: Centrifugal Force, physics, Newton, Law of Inertia, velocity, centripetal, Ron Kurtus, School for Champions. Copyright © Restrictions
Centrifugal Force Caused by Inertia
by Ron Kurtus (revised 1 September 2014)
When you swing an object around on a string or rope, you will feel a force pulling the object outward. This is called the centrifugal force and is caused by the inertia of the object, where it seeks to follow a straight-line path. It is called a resistive force or an inertial force.
Objects will move on a curved path if a centripetal force is applied to the object at an angle to the straight-line motion. The centrifugal force acts in the opposite direction of the centripetal force and is equal in magnitude. Although some sources call centrifugal force a virtual or false force, it certainly seems real to the person holding the rope.
There are various examples of the centrifugal force, which use the same equation as for centripetal force.
Questions you may have include:
- What causes centrifugal forces?
- What are some examples of centrifugal force?
- What is centripetal force equation?
This lesson will answer those questions. Useful tool: Units Conversion
Centrifugal force is resistive
When an object is following a curved path due to a centripetal force, it exhibits an equal force in the opposite direction.
Newton's Third Law or Action-Reaction Law states that for every applied force, there is an equal and opposite force. In other words, when you apply a force on a rope in swinging an object around you, you will feel an equal and opposite force pulling the object away from you. This is the centrifugal force.
Note: Many Physics sources say that centrifugal force is a fictitious or pseudo (false) force. This is contrary to the fact the you can feel the force.
Also, they seem to have forgotten Newton's Third Law. If they would have applied the Law, they would have seen that the centrifugal force is equal and opposite the centripetal force.
Centrifugal force is a resistive or inertial force in that it resists changing the direction or velocity of the object.
Examples of centrifugal force
There are various examples of applications of centrifugal inertial force.
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
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 carnival 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.
Equation for centrifugal force
The equation for the centrifugal force is the same as that for the centripetal force causing an object to follow a curved path is:
F = mv2/r
- F is the force pulling object away from center
- m is the mass of the object
- v is the straight line velocity of the object
- r is the radius of curvature cause by the 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.
A centrifugal force is the outward inertial force on an object moving along a curved path. 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
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)
Questions and comments
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Centrifugal Force Caused by Inertia