What is Centrifugal Force?

Ken Black

Centrifugal force is the force which describes the outward pressure that is exhibited around an object rotating around a central point. Its definition is based on a Latin phrase which means "fleeing the center," an accurate description based on what is being observed. There are some physicists who claim that true centrifugal forces do not exist, that an object's reaction to such a force can be explained by other means.

Scientist placing a test tube in a centrifuge.
Scientist placing a test tube in a centrifuge.

One possible explanation for centrifugal force rests in Newton's law of inertia. This law states that an object in a uniform motion tends to stay in that same motion unless there is pressure exerted by an outside force. For example, a ball being twirled around on a string would tend to go in a straight line if not for the string and the force the string puts on the ball. Therefore, the ball, instead of going in a straight line, goes in a circular motion around the center of the pivot.

A lab centrifuge spins blood samples to separate the solids from the liquids, which makes it better for detecting certain conditions.
A lab centrifuge spins blood samples to separate the solids from the liquids, which makes it better for detecting certain conditions.

This explanation, why easily understandable, does not explain all aspects of centrifugal force. For example, why does the force still exist when there is no string? In such cases, there is likely still going to be an outside force exhibiting pressure on the object, keeping it from going in a straight line. This is likely to include a cylinder.

Though the concept is not readily understood, the benefits of what many people refer to as centrifugal force are used for the benefit of mankind. For example, centrifugal force is what dries clothes in a dryer. Along with the heat that is used, the dryer also spins the clothes, much like a washing machine does, to get the majority of water out of them before the dryer finishes the job.

The medical community often uses a device specifically for creating a centrifugal force -- something commonly called a centrifuge. This spins blood samples to separate the solids from the liquids, which makes it better for detecting certain conditions. With the blood spinning, the heavier portions tend to settle toward the bottom of the vial.

In the end, centrifugal force may yet be explained away. However, the nice thing about the phenomenon is that it is not necessary to fully understand it in order to take advantage of it. The effects are clear and the benefits derived from the force are numerous.

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Discussion Comments


There is untold confusion regarding centrifugal force, yet the concept is very simple. If you swing a ball on a piece of string the ball "exerts" a centrifugal force on you hand, your hand, in its turn, exerts a centripetal force on the ball. You can see from this the ball is "exerting" a centrifugal force, it is not subject to such a force.

If a rotating mass was subject to both centripetal force and a centrifugal force, which many sources claim, these forces would cancel each other out, thus nothing would rotate. --Frank S.


Do you know that Newton proved himself wrong using his so called laws? What was said about this? If you did not know this I suggest you do a bit of research.

If there is no such thing as centrifugal force, explain this: A slowly spinning disc has a bar attached via a hinge, attached to the bar is a weight. The bar and weight are trailing the disc, If the disc suddenly spins faster the bar with the weight will no longer be dragged behind but will move in the direction the disc is moving overcoming drag and aligning as far from the center as possible.


The centripetal force acting on us (on the surface of the earth) is the gravitational force. The Earth pulls us down due to gravity, the reaction to this centripetal force is (by Newton's third) we pull the Earth up. I weigh 200 lbs., consequently, the Earth weighs 200 pounds relative to me.

This is why persons at or near the equator weigh less than they would near the poles. They weigh less because they have a high linear velocity because they are traveling a greater distance in a 24 hour period.


I am sure anon103738 knows that gravity holds us on this earth. But you yourself stated that we would all float into space with no gravity, so are you saying that the earth doesn't spin fast enough to throw us off?

Correct me if I am wrong, but as I understand centripetal force, it stops things escaping when spinning fast enough to overcome gravity. What is the equal and opposite force to centripetal force? science is only dumbed down because we teach lots of theories that become its now thought. The open mind will solve problems.


Anon30877 is correct.

Yes, you can use it to explain to kids in Grade 4, but we expect when they get to high school and university they can understand moving frames of reference, which is the only place where centrifugal forces exist.

anon103738: The earth does need centripetal force. That force is caused by gravity. Else, we'd all float into space. And no "so called experts" ever said that it would go straight out.

A dryer bleeds the water out of clothes not because of centrifugal forces, but because the dryer itself holds the clothes in (centripetal force) but the moisture in the clothes are not held back by anything, hence they flow out.

I think we should just stop lying to kids and just explain. If you keep dumbing science down we'll never have advancements.


So you're going to call it (a lack of centripetal force) are you, anon 30877? That's clever. Kids won't get confused at all. Did you know that the earth doesn't need centripetal force as it doesn't spin fast enough in relation to its diameter?. You got it at 1000mph is not fast enough because it only does one revolution in 24 hours, and you need revolutions per minute to get the centrifugal force effect.

Even then, a small diameter object (spinning) may need many r.p.m to create centrifugal force. Just think how fast the earth would be moving if did one r.p.m. it would be doing 1,440,000 m.p.h. I guess you would need that centripetal force then.

Stop quoting old clever people and become one yourself. We need to move on. When the so called experts say the object should go straight out if there is such a thing as centrifugal force, they seem to forget that it is being driven by the g: string in a direction as well as held back. So when you let go of the the string the object carries on in the direction it was driven at the same time it is moving away from the center in relation to where it would be on its circular path. Don't forget the air would slow it down because it's not being driven anymore.

So I suppose the "some physicists" could be wrong! what's your theory?


well, yeah, anon30877. The lack of centripetal force combined with the object's momentum which at any given moment is tangent to the circle.


The "some physicists" are right. There is no such thing as centrifugal force. What it actually is is a lack of centripetal force and can also be explained by Newton's first law.

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