Can Centripetal Force create Gravity?

Click For Summary

Discussion Overview

The discussion centers around the concept of whether centripetal force can create effects similar to gravity, particularly in a spinning framework containing fluids or gases. Participants explore the implications of spinning systems, artificial gravity in spacecraft, and the behavior of gases under different forces.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that a spinning framework could theoretically create conditions where a mass of liquid remains at the center, depending on the relationship between the densities of the gas and liquid involved.
  • Others argue that a spinning fluid would naturally tend to move outward, as seen in centrifuge operations, and question the assumption that gas would travel toward the center.
  • A participant suggests that the concept of artificial gravity in spacecraft relies on spinning to simulate gravitational effects, but acknowledges that this is not equivalent to real gravity due to the presence of Coriolis forces.
  • There is a discussion about the role of gravity as a centripetal force, with some participants asserting that gravity is what keeps celestial bodies together, while others challenge the distinction between centripetal and gravitational forces.
  • Questions arise regarding whether gas molecules can be bound by centripetal force and how gravity influences them differently, with references to the behavior of gases in a hypothetical rotating box with holes.
  • Some participants clarify that centripetal force is not a physical force in itself but rather a kinematical concept, emphasizing the importance of real forces such as electrostatic repulsion in the context of gas behavior.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the behavior of gases and liquids in spinning systems, with no consensus reached on the relationship between centripetal force and gravitational effects.

Contextual Notes

Participants note limitations in understanding the behavior of gases under centripetal force, including the significance of molecular interactions and the conditions that must be met for different forces to act effectively.

oragami
Messages
4
Reaction score
0
What I'm trying to get at is this, can a spinning framework of rings build enough centripetal force to keep a mass of liquid at the centre of the frame work? And if so what would be the relationship and conditions that would have to be met?
Really need help:|
 
Astronomy news on Phys.org
A spinning fluid would tend to go the outside, not toward the center. That is the principal of the centrifuge.
 
well thank you mathman
 
but i ment if the sphere was spinning and like a gas was in it, if most of the gas would travel towards the centre. Please advice
 
Is that the whole notion behind artificial gravity in a spacecraft ? A spinning spacecraft can reproduce the effects of gravity if I am not mistaken?
 
Last edited:
oragami said:
but i ment if the sphere was spinning and like a gas was in it, if most of the gas would travel towards the centre. Please advice

The gas will not go to the center. Why do you think it would?
 
oragami said:
but i ment if the sphere was spinning and like a gas was in it, if most of the gas would travel towards the centre. Please advice
NO, it wouldn't. It would travel toward the circumference. That was mathman's point.
 
math_04 said:
Is that the whole notion behind artificial gravity in a spacecraft ? A spinning spacecraft can reproduce the effects of gravity if I am not mistaken?
People walking on the inside wall of the spinning spacecraft (heads pointed toward the axis of rotation) would feel a force pushing them against the space craft. Than can "simulate" gravity but will not be exactly the same. For example, in all but an immense space craft, coriolis forces would be evident.
 
A spinning fluid mass would resemble a galaxy in deep space. Gravity limits the effects of centripetal force.
 
  • #10
Chronos said:
A spinning fluid mass would resemble a galaxy in deep space. Gravity limits the effects of centripetal force.

I have no idea what you are trying to say? In a galaxy gravity is what provides the centripedal force that keeps it together??
 
  • #11
Wallace said:
I have no idea what you are trying to say? In a galaxy gravity is what provides the centripedal force that keeps it together??
In a galaxy the centripetal force is gravity.
 
  • #12
Yes, that's what I said? At least that was what I intended to say...
 
  • #13
oragami said:
What I'm trying to get at is this, can a spinning framework of rings build enough centripetal force to keep a mass of liquid at the centre of the frame work? And if so what would be the relationship and conditions that would have to be met?
Really need help:|

Yes...Theoreticaly this is possible. For simplisity sake take for example a ring and contain within it two elements... one a gas and other liquid. Let the gas be significantly "heavier" than the fluid. When spinning centripetal force would pull the heavy gas to the outside and leave the fluid (lightier) in the center...Is this even what you are asking?
 
Last edited:
  • #14
However, I don't know of any Gas heavier than liquid... so in accuality I don't think so
 
  • #15
So is the difference in behavior mainly due to the atomic freedom that exists in gasses

Does this amount to saying that randomly circulating gas molecules cannot be bound by the centripetal force?

How does gravity keep them together, is gravity stronger than centripetal force?
 
  • #16
raknath said:
Does this amount to saying that randomly circulating gas molecules cannot be ?bound? by the centripetal force?

How does gravity keep ?them? together, is gravity stronger than centripetal force?

Can you please explain in more depth what you are saying? What centripetal force are you referring to??
 
  • #17
raknath said:
So is the difference in behavior mainly due to the atomic freedom that exists in gasses

Does this amount to saying that randomly circulating gas molecules cannot be bound by the centripetal force?

How does gravity keep them together, is gravity stronger than centripetal force?
Several levels of issues here:

1) One is called 'miscibility' see: http://en.wikipedia.org/wiki/Miscibility

2) Whether 'randomly circulating gas molecules' are 'bound' depends on their energy and strength of the forces involved.

3) In this particular case, the substances appear to be already contained -- according to the original question. So this should not be an issue.

4) Actually, in the case as presented -- a gas -- the presence of gravity or centripetal or any force is really unimportant. The gas is going to fill the volume.

5) A liquid would only maintain being a liquid in the presence of additional gas (of some kind) filling any extra volume (or vaporize to expand to fill the volume)

6) If the containing object (spaceship) is spinning, the denser material will settle against the outer 'walls'.
 
Last edited:
  • #18
Consider a box with some gas and a lot of holes(very hypothetically)

Let us say i send the box into revolutions, now by what we have seen the gas would escape out of the holes, as the box rotates?

Now however if the gas is gravitationally bound like it is for say jupiter, the gas does not escape, i mean why is this any different? Does this mean that gravity influences gas molecules differently than it is affected by centripetal force?
 
  • #19
raknath said:
Consider a box with some gas and a lot of holes(very hypothetically)

Let us say i send the box into revolutions, now by what we have seen the gas would escape out of the holes, as the box rotates?

Now however if the gas is gravitationally bound like it is for say jupiter, the gas does not escape, i mean why is this any different? Does this mean that gravity influences gas molecules differently than it is affected by centripetal force?

A centripetal force is one that acts toward the center, so gravity is a centripetal force.

In your spinning box, the centripetal force is supplied by the walls of the box pushing inward on the gas preventing the molecules from following a straight line path as would be natural to them. When you put holes in the box, you have areas where there is no centripetal force to contain the gas and it escapes.
 
  • #20
Janus said:
A centripetal force is one that acts toward the center, so gravity is a centripetal force.
Better: Gravity is a central force. Centripetal force is a kinematical rather than dynamical concept. This page, http://encyclopedia.stateuniversity.com/pages/3970/centripetal-force.html explains central versus centripetal versus centrifugal forces in a nice, simple manner.

raknath said:
Now however if the gas is gravitationally bound like it is for say jupiter, the gas does not escape, i mean why is this any different? Does this mean that gravity influences gas molecules differently than it is affected by centripetal force?
What centripetal force? You are acting as if centripetal force is something real in and of itself. It isn't. The real (i.e., physical) force in your rotating box is the electrostatic repulsion between the surface of the box and the gas molecules that hit it. The mass of the gas itself is insignificant. The real force in the case of Jupiter is the mass of all the stuff that comprises Jupiter. Compare this to the gas in a box situation. The gravitational force exerted by the gas on a gas particle near the surface of the box (or anywhere inside the box) is immeasurably small.
 
Last edited by a moderator:
  • #21
Janus said:
When you put holes in the box, you have areas where there is no centripetal force to contain the gas and it escapes.

Why so?

The holes are covered with air which in turn would be atttracted towards the center so there should be a force the air exerts towards the center, won't it?

However the reaction force of th gas still wins, how?
 
  • #22
D H said:
What centripetal force? You are acting as if centripetal force is something real in and of itself. It isn't. The real (i.e., physical) force in your rotating box is the electrostatic repulsion between the surface of the box and the gas molecules that hit it. The mass of the gas itself is insignificant. The real force in the case of Jupiter is the mass of all the stuff that comprises Jupiter. Compare this to the gas in a box situation. The gravitational force exerted by the gas on a gas particle near the surface of the box (or anywhere inside the box) is immeasurably small.

No i am a little confused, Are you saying that the sum total of the force exerted by all the particles of the gas is too less to actually get affected by the centripetal force or is it that each molecule is actually never effect and it is the sum effect that we see manifesting. So every molecule is free to do as it pleases?
 
Last edited:
  • #23
raknath said:
Why so?

The holes are covered with air which in turn would be atttracted towards the center so there should be a force the air exerts towards the center, won't it?

However the reaction force of th gas still wins, how?

What force? Draw a free body diagram.

You are acting as if centripetal force is a real force. It isn't. Centripetal force is a kinematic force -- it is just a label we slap on the kinematics when the acceleration is, for whatever reason, observed to be directed toward some center.

Suppose this box (without holes) and the gas inside initially are non-rotating. Now start the box rotating. Aerodynamic drag will make the layer of the gas near the surface of the box more-or-less move with the box. This is called the "no-slip condition". A video: .

If you have a fan to keep you cool in the summer, look at the blades. They're probably a bit dirty. They are dirtiest exactly where you wouldn't expect it: Right where the air flow is greatest. That's the no-slip condition at work. Any dust that happens to hit the blade might well stick to the blade due to adhesion. It is adhesion between the air molecules and the fan blade that is responsible for this boundary layer effect. Because the boundary layer is pretty much at rest with respect to the blades, the motion of the blade through the air will not blow the dust off. Because the air flow constantly refreshes the boundary layer, there is an influx of new dust particles that can stick to the blade.

Back to the box that is just starting to rotate. Away from the gas/box boundary the gas is still not rotating. There is a wind inside the box. This wind transfers momentum from the boundary layer to the non-rotating gas. Eventually the entire contents of the box will be rotating (and the wind will vanish).

The only forces acting on a parcel of air in this box are gravity and the electrostatic force. The adhesion that is responsible for the no-slip condition is an electrostatic effect. The viscosity of the gas that creates the wind that in turn makes the entire box rotate is also an electrostatic effect.
 
Last edited by a moderator:
  • #24
Ok i guess i was a little vague before. I was thinking of the magnetic levitation effect and was wondering if it was possible to achieve on an object at the centre of a series of rotating frame works?

JCOX said:
Yes...Theoreticaly this is possible. For simplisity sake take for example a ring and contain within it two elements... one a gas and other liquid. Let the gas be significantly "heavier" than the fluid. When spinning centripetal force would pull the heavy gas to the outside and leave the fluid (lightier) in the center...Is this even what you are asking?

So yes only that I'm considering one element either liquid of solid
 
  • #25
Thanks DH that helps :)
 

Similar threads

High School Trying to understand orbiting objects in space
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad Origin of Centripetal force when the net force toward the center is 0?
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad Why can centripetal force balance out gravity?
  • · Replies 23 ·
Replies
23
Views
3K
Washing machine - centripetal force
  • · Replies 25 ·
Replies
25
Views
6K
Undergrad Where is the centripetal force acting on mass M?
  • · Replies 21 ·
Replies
21
Views
3K
High School Confusion while trying to build intuition of centripetal force
  • · Replies 15 ·
Replies
15
Views
4K
Undergrad How do we provide centripetal force in this situation?
  • · Replies 16 ·
Replies
16
Views
3K
Undergrad Remark on centrifugal force in Heino Falcke's black hole book
  • · Replies 22 ·
Replies
22
Views
3K
Undergrad Gravity inside an exponential mass disk
  • · Replies 16 ·
Replies
16
Views
2K
Undergrad Effects of gravity on planetary core structure
  • · Replies 9 ·
Replies
9
Views
3K