# Centrifugal forces ' appear ' to act opposite to gravity . How is this possible?

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Posted today 31st March 2015

Through the General theory of Relativity ,produced by Einstein , we have learned that MASS produces a distortion in space in a proportion to that amount of mass involved.

As other fundamental forces have opposites . Eg

Electrical positive charge has negative charge as an opposite .

Magnetic fields appear to have North and South poles as opposites.

If Gravity is a fundamental attraction towards , caused by a certain type of distortion in space as Einstein indicated.

( A ). What is a possible opposite force or repulsion ?

( B ). How can these counter distortions be achieved ?

( C) . Can Centrifugal forces be utilised in this endeavour ?

Mike

Edited by Mike Smith Cosmos

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As every other force has opposites ( positive charge has negative charge as opposite . ) Magnetic fields can have North and South poles.

That is not every other force; it is one force (electromagnetism). That may be unique.

Edited by Strange
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That is not every other force; it is one force (electromagnetism). That may be unique.

Modified .

So if ,in the case of electricity we call the one force ' Electromagnetism ' , what do we call the forces like gravity ( gravitational attraction, centrifugal action, cosmological constant, Kashmir effect etc mechanical attraction, repulsion ) ?

Or are you saying , there is only one force. ' Electromagnetism ' and that is it !

Like ' Charge ' and it's effect, is all there is ? As regards to forces , that is ?

Mike

Edited by Mike Smith Cosmos
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There are four fundamental forces;

1)gravity

2)electromagnetism

3)strong

4)weak

All other forces are either residual effects of these, such as the residual strong nuclear force holding a nucleus together. Or they are fictitious forces that are due to our choice of coordinates, such as centrifugal force and the Coriolis force. You might even want to put gravity in the fictitious 'box' viz general relativity.

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Centrifugal and centripetal forces are not "kinds" of forces with their own mechanisms. They are labels we give to other forces under specific conditions. A centripetal force is one directed toward the center of a circle; that force must be due to one of the fundamental forces ajb has noted. In an orbit it's gravitational, in the case of a bucket on a rope it's the tension in the rope (which is ultimately electromagnetic).

Centrifugal and Coriolis forces are examples of pseudoforces that arise when we have a non-inertial coordinate system. Since there is acceleration (rotation), Newton's first law does not apply. We add in the pseudoforce to make the system look inertial. If you analyze the system from an inertial frame, the force is not there.

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There are four fundamental forces;1)gravity2)electromagnetism3)strong4)weakAll other forces are either residual effects of these, such as the residual strong nuclear force holding a nucleus together. Or they are fictitious forces that are due to our choice of coordinates, such as centrifugal force and the Coriolis force. You might even want to put gravity in the fictitious 'box' viz general relativity.

Do all these four types of forces have .. Attraction and repulsion namely both directions to the force ? Both towards and away from ? Or is it even possible for a force to be Uni-directional ? And How do we know that ? Or is the old adage " what goes up must come down ! ". Out of date ?

Mike

Centrifugal and centripetal forces are not "kinds" of forces with their own mechanisms. They are labels we give to other forces under specific conditions. A centripetal force is one directed toward the center of a circle; that force must be due to one of the fundamental forces ajb has noted. In an orbit it's gravitational, in the case of a bucket on a rope it's the tension in the rope (which is ultimately electromagnetic).

Centrifugal and Coriolis forces are examples of pseudoforces that arise when we have a non-inertial coordinate system. Since there is acceleration (rotation), Newton's first law does not apply. We add in the pseudoforce to make the system look inertial. If you analyze the system from an inertial frame, .. the force is not there....

.

. " the force is not there." You say !

Is the bit I have a problem with . Although I can probably not do the math you describe there with your. 'analyse the system from an inertial frame' bit . It puts me into a questioning mode ,when I remember all my experiences through my life where I have actually felt those centrifugal forces. A so called set of Observations .

Being the outside person on a skating chain going in a circle round an ice rink.

Being on a playground fast spinning roundabout, hanging on for dear life ,while being slung to the edge.

Feeling and seeing the water in the bucket above my head.

Throwing a discus.

Having to lean back while swinging a shot weight around me , on a rope.

Being driven round a tight bend , being pushed up against the passenger door.

I understand all the bit about , where you go if you let go, (strait forward) . But while I have not let go I " feel this force , pushing me or it , outward or upward .

The force does not feel fictitious , it feels very real . My senses tell me this to my very being !

As a motor cyclist I feel it daily , every corner I go round . So how can it be fictitious if I feel it so bad, and if I put a Newton meter there ,I am sure I could measure it . really measure the force ? It appears real . Measures real . How much more real must it be to be real .

Also there are all manner of devices that use these forces to extract material by filtration , spinning separators, centrifugal pumps, astronaut training rig , radioactivity refining centrifuges for nuclear power station fuels ,etc . How can these work if , centrifugal force is not real ?

Mike

Edited by Mike Smith Cosmos
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. " the force is not there." You say !

Is the bit I have a problem with . Although I can probably not do the math you describe there with your. 'analyse the system from an inertial frame' bit . It puts me into a questioning mode ,when I remember all my experiences through my life where I have actually felt those centrifugal forces.

Being the outside person on a skating chain going in a circle round an ice rink.

Being on a playground fast spinning roundabout, hanging on for dear life ,while being slung to the edge.

Feeling and seeing the water in the bucket above my head.

Throwing a discus.

Having to lean back while swinging a shot weight around me , on a rope.

Being driven round a tight bend , being pushed up against the passenger door.

I understand all the bit about , where you go if you let go, (strait forward) . But while I have not let go I " feel this force , pushing me or it , outward or upward .

The force does not feel fictitious , it feels very real . My senses tell me this to my very being !

As a motor cyclist I feel it daily , every corner I go round . So how can it be fictitious if I feel it so bad, and if I put a Newton meter there ,I am sure I could measure it . really measure the force ? It appears real . Measures real . How much more real must it be to be real .

Also there are all manner of devices that use these forces to extract material by filtration , spinning separators, centrifugal pumps, astronaut training rig , radioactivity refining centrifuges for nuclear power station fuels ,etc . How can these work if , centrifugal force is not real ?

The common theme is that you are moving in a circle somehow — that's an accelerated reference frame. If you do the analysis in an inertial frame, the forces are not there. What you (or the objects) experience is the tendency to go in a straight line, and you (or they) are feeling whatever force is creating the centripetal acceleration that's making you move in a circle. Naturally, you exert a force opposite of that.

Take going around a bend, and being pushed by the door. The door pushes on you. Your motion is determined by the forces exerted on you, not by you. So your motion is in a circle because the door is pushing you in. The force of you pushing out on the door is a result of Newton's third law, but that does not define your motion. There is no force acting ON you, pushing you out. The force acting ON you is pushing you in, keeping you from traveling a straight line.

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The common theme is that you are moving in a circle somehow that's an accelerated reference frame. If you do the analysis in an inertial frame, the forces are not there. What you (or the objects) experience is the tendency to go in a straight line, and you (or they) are feeling whatever force is creating the centripetal acceleration that's making you move in a circle. Naturally, you exert a force opposite of that.

Take going around a bend, and being pushed by the door. The door pushes on you. Your motion is determined by the forces exerted on you, not by you. So your motion is in a circle because the door is pushing you in. The force of you pushing out on the door is a result of Newton's third law, but that does not define your motion. There is no force acting ON you, pushing you out. The force acting ON you is pushing you in, keeping you from traveling a straight line.

Yes , I am sort of familiar with that explanation , but it feels so real , so ever so real , and it does get used ,in the examples I have quoted.

Quote

" I am sure I could measure it . really measure the force ? It appears real . Measures real . How much more real must it be to be real .

Also there are all manner of devices that use these forces to extract material by filtration , spinning separators, centrifugal pumps, astronaut training rig , radioactivity refining centrifuges for nuclear power station fuels ,etc . How can these work if , centrifugal force is not real ? "

Unquote

I need to go and think a bit !

Mike

Edited by Mike Smith Cosmos
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Do all these four types of forces have .. Attraction and repulsion namely both directions to the force ? Both towards and away from ? Or is it even possible for a force to be Uni-directional ? And How do we know that ? Or is the old adage " what goes up must come down ! ". Out of date ?

Gravity can be repulsive in very exotic situations, which we generally think are unphysical.

The strong force allows quarks and anti-quarks to be repelled, if they have the same colour charge. It is more complicated that in electromagnetic theory but you can discuss quark and anti-quark interactions to one-gluon exchange ('tree level') to get some insight.

The weak force is not seen as a 'binding force' in the same way as the other forces. I am not sure if one can really think in terms of attraction or repulsion here.

EDIT: Upon further thinking; As the weak force is mediated by spin 1 bosons it can be both attractive and repulsive. This will depend on the weak isospin spin or the weak hypercharge, I am not sure.

Edited by ajb
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Yes , I am sort of familiar with that explanation , but it feels so real , so ever so real , and it does get used ,in the examples I have quoted.

Quote

" I am sure I could measure it . really measure the force ? It appears real . Measures real . How much more real must it be to be real .

Think about this (or perhaps even do the experiment, if you need to). The bucket swinging in a circle, but put a spring scale at the end. Now think about the force a spring scale exerts — it's a restoring force. It does not push out, it pulls in. The bucket is being pulled in, it is not being pushed out, and you can measure the amount of force. But you do not measure anything pushing out.

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Gravity can be repulsive in very exotic situations, which we generally think are unphysical.The strong force allows quarks and anti-quarks to be repelled, if they have the same colour charge. It is more complicated that in electromagnetic theory but you can discuss quark and anti-quark interactions to one-gluon exchange ('tree level') to get some insight.The weak force is not seen as a 'binding force' in the same way as the other forces. I am not sure if one can really think in terms of attraction or repulsion here.

How do you guys get your head around all this stuff, I suppose you are happy seeing it in maths form , I need to visualise things going hither and thither , pushing and being shoved , pulled or whatever , and some of it is SO CONTORTED , I have to watch I do not go STARK STARING BONKERS and insane .

It's all gone black , I think I may have blown a fuse in my brain !

Oh no ! It was my I-pad just ran out of charge . Oops ! I need to recharge !

"" You can do this with quark anti quark scattering at tree level. You can extract a short distance potential.

For the singlet structure you get a -1/r potential. For the color octet you get a 1/r potential. ""Quote Ajb

Ahhhhhhhh! He ran screaming from the building and jumped in a duck pond !

Mike

Edited by Mike Smith Cosmos
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How do you guys get your head around all this stuff, I suppose you are happy seeing it in maths form , I need to visualise things going hither and thither , pushing and being shoved , pulled or whatever , and some of it is SO CONTORTED , I have to watch I do not go STARK STARING BONKERS and insane .

Such classical thinking will not help you with understanding the strong or weak forces. You need to calculate something and then maybe you can look at quasi-classical results to get a more 'mechanical picture'. You can do this with quark anti quark scattering at tree level. You can extract a short distance potential.

For the singlet structure you get a -1/r potential. For the color octet you get a 1/r potential.

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Such classical thinking will not help you with understanding the strong or weak forces. You need to calculate something and then maybe you can look at quasi-classical results to get a more 'mechanical picture'. You can do this with quark anti quark scattering at tree level. You can extract a short distance potential.For the singlet structure you get a -1/r potential. For the color octet you get a 1/r potential.

Can you explain that to me ?

Mike

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Can you explain that to me ?

Mike

!

Moderator Note

No - not here he cannot. Much as I would enjoy AJB's explanation, this a thread on centrifugal force not on QCD.

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Sorry imfamatal .

Also sorry you were right about need for two bodies , in centrifugal force , issue , for Newton's third law.

This does not remove the idea of two forces alone , one against the other , outside Newton's third law though , does it .

Like one team pulling on a rope ( tug of war ) that way , and another team pulling the other way .

If one dominates with its pull force ( they win ) . If they both are equal ( it is balanced and they stay still in a balanced condition. Or have I got that wrong too.

I know swansont says it's not true for all atomic orbits and lines but I saw an old text book , where centripetal was the attractive charge between electron and nucleus , and centrifugal was speed in orbit of the electron. Balanced into orbit. I know this is pre quantum . But it did give a right answer for some simple orbits .

Mike

Edited by Mike Smith Cosmos
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I know swansont says it's not true for all atomic orbits and lines but I saw an old text book , where centripetal was the attractive charge between electron and nucleus , and centrifugal was speed in orbit of the electron. Balanced into orbit. I know this is pre quantum . But it did give a right answer for some simple orbits .

You'll need to find the book to show this. The Bohr model only had one force in it: electrostatic. The orbit was circular, to the centripetal condition applied, other condition was that angular momentum was quantized. That's it.

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You'll need to find the book to show this. The Bohr model only had one force in it: electrostatic. The orbit was circular, to the centripetal condition applied, other condition was that angular momentum was quantized. That's it.

?

Here is a Wikipedia reference to it. but describing the Centrifugal force. .

http://www.3rd1000.com/chem101/chem104i.htm

Note the mention of his view of centrifugal force in this context .

Quote "

The Bohr model of an atom postulated a structure in which a single electron moved in a circular orbit around the central nucleus, much as a satellite orbits the earth or the planets orbit the sun. Satellites may circle the earth at any distance outside the atmosphere; their orbits may have any radius. As a satellite travels in its orbit there is a balance between the inward force of gravitation, mm'g/r2, and the outward or CENTRIFUGAL force of the moving satellite, mv2/r. In these equations m is the mass of the satellite, m' is the mass of the central earth, r is the radius of the orbit, and v is the velocity of the satellite in its orbit. The forces are equal in a stable orbit; mm'g/r2 = mv2/r gives by rearrangement v2r = m'g. Since the mass of the earth m'and the gravitational constant g are both constants, a satellite can assume an orbital radius if and only if it possesses the appropriate velocity. Acceleration of the satellite must therefore increase both its velocity and its orbital radius so it moves outward, while deceleration will move it inwards. Astronauts use this procedure, decelerating their capsules or shuttles by firing rockets to move inward until they reenter atmosphere.

" Unquote

[in the atomic orbit version , the inward force centripetal is electrostatic force between electron and nucleus , not gravity]

Mike

Edited by Mike Smith Cosmos
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Can you explain that to me ?

It would be a bit off topic as already noted, and I am not sure I could really teach you QCD. I am not really the person to ask for this. Anyway, your question was if the strong force can be attractive and repulsive. The answer is yes.

Maybe it is worth noting that 'mechanical forces' are residual effects of the electromagnetic force. The atoms in the material cannot actually come into contact as there is electrostatic repulsion between the electrons of the atoms. (This is a somewhat simplified story)

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It would be a bit off topic as already noted, and I am not sure I could really teach you QCD. I am not really the person to ask for this. Anyway, your question was if the strong force can be attractive and repulsive. The answer is yes.Maybe it is worth noting that 'mechanical forces' are residual effects of the electromagnetic force. The atoms in the material cannot actually come into contact as there is electrostatic repulsion between the electrons of the atoms. (This is a somewhat simplified story)

Strange was also indicating that " electromagnetic " might be ( All there is ) , is this a common belief ? There appears to be a focusing in on " electromagnetism " .

Swansont was saying that , electrostatics was the original centripetal force to do with early theories of atoms, ( which I sort of knew ) and I have just quoted from Wikipedia , that Bohr thought this was balanced with centrifugal force in the atom . ( post 17 on this thread ) . So maybe , just maybe I am in good company . ( I know that is no merit ,as he could have been my grandfather, that would still not make it right) ( he was not my grandfather ) .

Mike

Edited by Mike Smith Cosmos
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Strange was also indicating that " electromagnetic " might be ( All there is ) , is this a common belief ?

Not that all there is, most simple mechanical problems also take gravity (Newtonian) into account.

Another example to think about are objects at rest on inclined planes. The friction is a phenomenological force that is ultimately electrostatic in nature. Friction arises due to the interatomic and intermolecular forces between the surface of the object and the plane. This makes deriving friction from first principles impossible and so we model it phenomenologically understanding it is not a fundamental force.

Edited by ajb
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Not that all there is, most simple mechanical problems also take gravity (Newtonian) into account.Another example to think about are objects at rest on inclined planes. The friction is a phenomenological force that is ultimately electrostatic in nature. Friction arises due to the interatomic and intermolecular forces between the surface of the object and the plane. This makes deriving friction from first principles impossible and so we model it phenomenologically understanding it is not a fundamental force.

.

.

so we could be into just " Gravity and ElectroMagnetism " being . .ALL THERE IS ? As regards Forces .

Mike

Edited by Mike Smith Cosmos
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Swansont was saying that , electrostatics was the original centripetal force to do with early theories of atoms, ( which I sort of knew ) and I have just quoted from Wikipedia , that Bohr thought this was balanced with centrifugal force in the atom.

The Bohr model is very 'mechanical' and classical. In quantum mechanics the electron and proton are still bound by the Coulomb potential.

so we could be into just " Gravity and ElectroMagnetism " being . .ALL THERE IS ? As regards Forces .

No, you need to explain the nuclear force that binds nucleons in a nucleus. This led people to the strong force and quantum chromodynamics.

Then you have to explain beta decay. This led to the weak force.

Edited by ajb
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The Bohr model is very 'mechanical' and classical. In quantum mechanics the electron and proton are still bound by the Coulomb potential.No, you need to explain the nuclear force that binds nucleons in a nucleus. This led people to the strong force and quantum chromodynamics.Then you have to explain beta decay. This led to the weak force.

But surely the weak force is the " electroweak " force so it is already tied into ' electro '.

Is the strong force in quarks not related to charge ? I see in some tables of the standard model, there are + and - all over the place .

Can all this not be at the root of this centripetal - centrifugal dance , that Bohr suggested ,was going on in the atom. .?

I know the issues get complicated when more than one electron is present. But does the hydrogen atom not lead , in this analysis ?

Mike

Edited by Mike Smith Cosmos
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But surely the weak force is the " electroweak " force so it is already tied into ' electro '.

This depends on the energy scale we are talking about. For the discussion of atomic physics we can assume that the electroweak force is broken into the electromagnetic and weak force. We are no where near the elecroweak scale.

Is the strong force in quarks not related to charge ? I see in some tables of the standard model, there are + and - all over the place .

Not electric charge, but color charge.

Can all this not be at the root of this centripetal - centrifugal dance , that Bohr suggested ,was going on in the atom. .?

Electromagnetism is the root of all chemistry.

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Sorry imfamatal .

https://youtu.be/R7GeKLE0x3s?t=10m45s

Well not actually - but close

This does not remove the idea of two forces alone , one against the other , outside Newton's third law though , does it .

Like one team pulling on a rope ( tug of war ) that way , and another team pulling the other way .

If one dominates with its pull force ( they win ) . If they both are equal ( it is balanced and they stay still in a balanced condition. Or have I got that wrong too.

No - that's fine so far. But Newton's first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.

If centripetal (inwards radial) was balanced (ie by an outwards radial) then the object would continue in a straight line! The Centripetal force is calculated as that force needed to accelerate the mass inwards - ie to stop it continuing in a straight line.

The "balanced condition" is a straight line. An orbit is motion under acceleration - acceleration is an imbalance of forces.

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