# If the centrifual force does not exist then why?

1. Jul 29, 2010

### zeromodz

If the centrifugal force does not exist, then why in space where there is little friction do spinning objects tend to flatten out. Like Jupiter's rings for instance, they are sooo thin. What makes them so thin. The only thing I can think of is the centrifugal force flattening it out.

Centrifugal force = mrw^2

2. Jul 29, 2010

### brainstorm

Generally, I think what you are calling "centrifugal force" is explained as momentum/velocity in the opposite direction as a centripetal force due to motion.

I'm not sure why the rings of a planet flatten out but might it have to do with the gravitational field of the planet rotating along the planet's axis? Are there any planets with rings that aren't perpendicular to the axis of rotation?

It's a good question. I hope someone has an answer for it.

3. Jul 29, 2010

### mikelepore

When they say that the so-called centrifugal force is fictitious, they don't mean that it doesn't exist -- they mean that "force" isn't the correct word to describe the effect. There is no external agency pulling on the object in the outward direction by applying a force to it. The tendency of mass to move in a straight line is producing the effect.

4. Jul 29, 2010

### novop

You're referring to the centripetal force, not the centrifugal force, and it is very real. What happens when you go around a curve in your car? You feel a force pulling you to the outside of the curve. That's exactly why planets are fatter around their belt and why rings form.

5. Jul 29, 2010

### K^2

Words "fictitious force" mean that it is a real force, but it only manifests in certain coordinate systems. More specifically, accelerated ones.

If you go to coordinate system which rotates with object in question, you have to add centrifugal force to account for dynamics.

If you are in an inertial coordinate system, there is no need for centrifugal force to describe what's going on. If you account for all the forces acting on particles forming the rings, you will get the correct dynamics without including centrifugal force into consideration.

6. Jul 29, 2010

### rcgldr

There's also the laymans (non-physicsist) version of the term centrifugal force, which refers to the reaction force due to centripetal force. The issue physicists have is using the term centrifugal force to describe the reaction force (which is a real force). As long as it's qualified as a "reactive centrifugal force" then there should be no confusion. Wiki article:

http://en.wikipedia.org/wiki/Reactive_centrifugal_force

7. Jul 29, 2010

### brainstorm

What is the problem with recognizing two distinct physical tendencies here: 1) centripetal forces such as gravity, which attract matter toward a center; and 2) Inertia, by which objects in motion tend to move in a straight line except when acted upon by another force. Objects revolving around an axis have inertia that causes them to tend to remain in (linear) motion tangential to the path of their orbit. Yet they are centripetally forced toward the center by whatever binds them to it, whether gravity or a rope or the resistance of joints to let go of their sockets.