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Offline Bass

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Does centrifugal force actually exist?
« on: 09/08/2005 17:38:30 »
Does centrifugal force actually exist- that is, is there actually a force that pushes objects away from a center of rotation?  There are times I can feel as though I'm being pushed away from a center of rotation- but are these "inertial" forces in my frame of reference?
And if it does exist, does that mean that centripetal forces also exist?  Or are centripetal forces actually other forces (gravity, reaction forces, etc.)?

Prediction is difficult, especially the future.  -Niels Bohr


 

Offline ukmicky

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Re: Does centrifugal force actually exist?
« Reply #1 on: 09/08/2005 21:04:54 »
The force youíre talking about is the Coriolis force and yes its effects are real.
The Coriolis force is the main problem that we would face if we tried to
build a spaceship using a centrifuge  as a way to produce artificial gravity.
If the spinning section of your ship was too small your astronauts would all get dizzy unless they all walked in the direction of spin.
also try sitting a roundabout thatís spinning fast and see how hard it is to control any part of your body.

The human brain can however adapt to the Coriolis force quite quickly providing its effects are keep to a minimum. But this would mean the rpm of any spinning habitat is kept below 3 rpm.  I read somewhere that this would mean that in order to obtain a 1G loading on the human body the radius of any habitat would have to be between 750 to 1000 meters.  (Thatís big) and totally beyond what we could put in space at present


Off the subject slightly I cant see why NASA cant use electro magnets and tight fitting clothes stitched with metallic strands as a form of artificial gravity.
A 1G force should be easy to achieve using electro magnets, as the electromagnetic force is a much stronger force compared to gravity
The power required to operate such a system of electro magnets wouldnít be enormous and they would also only need to be active when someone is in the vicinity of each magnetic plate, and computers can be shielded quite easily
NASA are also looking at a magnetic shielding system for protection against solar radiation it would shield the crew compartments like the earths magnetosphere


And a magnet force penetrating the human body can also be highly beneficial. It cuts pain, aids new cell growth, strengthens bones, the list goes on and on..  It would actually a good thing to use just for the health benefits on a space ship
As it would help combat many of the health problems arising through long duration spaceflight.




« Last Edit: 10/08/2005 02:29:20 by ukmicky »
 

Offline simeonie

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Re: Does centrifugal force actually exist?
« Reply #2 on: 09/08/2005 21:16:50 »
There was this ride at the fair I went to and there was this massive kind of circle thingy with a cage around it.

You just had to stand up in it and the ride went nearly right up on it's side and everything while spinning. You weren't strapped in or anything. Is this a result of centrifugal force?

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Offline Ultima

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Re: Does centrifugal force actually exist?
« Reply #3 on: 09/08/2005 21:21:24 »
Simeonie yup that's caused by what's commonly referred to as "centrifugal force"... however centrifugal force doesn't exist!

My physics teacher would bitch slap me in the face if he heard me say centrifugal :P force, it's centripetal force. I learnt the hard way :) from a scary welshman, you dont have to:

http://hyperphysics.phy-astr.gsu.edu/hbase/cf.html

Centripetal force is what keeps things in orbit too, you learn all that in ALevel Physics.. not sure what the American equivalent is.

wOw the world spins?
« Last Edit: 10/08/2005 22:54:00 by Ultima »
 

Offline ukmicky

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Re: Does centrifugal force actually exist?
« Reply #4 on: 09/08/2005 21:42:21 »
Ultima
My English teacher and physics teacher would of both bitch slapped me if I had spelt
centrifugal as  centrafeugal

Handy that editing feature:)
« Last Edit: 09/08/2005 21:43:37 by ukmicky »
 

Offline gsmollin

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Re: Does centrifugal force actually exist?
« Reply #5 on: 09/08/2005 21:44:17 »
Yea, I jumped to the bottom here to say that, and found Ultima beat me. However, I don't think my old freshman physics teacher was the bitch-slappin' type...

What we call "uniform circular motion" in the Newtonian physics book applies an acceleration to a particle that always points to the center of the circle, and always orthogonal to the tangent velocity vector. The acceleration is central-seeking or centripetal. The acceleration is produced by a centripetal force, f=ma.

Centrifugal force is a reaction force that we feel as we are the object being accelerated towards the center of a circle, or radius, such as in a turn. We feel every part of our body being pressed towards the seat of the carnival ride, for instance. We then say we have felt the centrifugal force, but it is only a reaction to the centripetal force that is causing the acceleration.
 

Offline Bass

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Re: Does centrifugal force actually exist?
« Reply #6 on: 09/08/2005 23:55:27 »
Since I study rocks and know just enough physics to be dangerous- I'm still trying to figure this out.  Is there a separate centripetal force?  It seems that in orbitting celestial bodies it is actually gravity, or the tension in a string when whirling a rock about your head, or the reaction force of the road against your tires as you squeal around a turn?
Is centrifugal force really a measure of the change in inertia?  When I whirl a rock around my head and let go, it travels at a tangent to it's circular motion (perpendicular to the radius at the point it is let go).  If centrifugal force actually exists, shouldn't it travel directly away from the center of rotation?

Prediction is difficult, especially the future.  -Niels Bohr
 

Offline simeonie

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Re: Does centrifugal force actually exist?
« Reply #7 on: 10/08/2005 11:49:49 »
Is G-Force similar to 'centrifugal' force. Although apparently centrifugal force doesn't exist..... so why make it up? I am a little confused :S

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Offline gsmollin

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Re: Does centrifugal force actually exist?
« Reply #8 on: 10/08/2005 21:01:40 »
quote:
Originally posted by Bass

Since I study rocks and know just enough physics to be dangerous- I'm still trying to figure this out.  Is there a separate centripetal force?  It seems that in orbitting celestial bodies it is actually gravity, or the tension in a string when whirling a rock about your head, or the reaction force of the road against your tires as you squeal around a turn?
Is centrifugal force really a measure of the change in inertia?  When I whirl a rock around my head and let go, it travels at a tangent to it's circular motion (perpendicular to the radius at the point it is let go).  If centrifugal force actually exists, shouldn't it travel directly away from the center of rotation?

Prediction is difficult, especially the future.  -Niels Bohr



The centripetal force is the force accelerating the rock towards you, in the center who are whirling it about you. This force has a magnitude equal to the tension in the string, and a rotating direction that always points at you in the center. Centrifugal force is the reaction force that you feel on the other end of the string, which seems to be pulling the rock away from you. If you let go of the string, the rock flies off in a straight line, since the centripetal force is now zero.
« Last Edit: 10/08/2005 21:04:40 by gsmollin »
 

Offline Bass

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Re: Does centrifugal force actually exist?
« Reply #9 on: 10/08/2005 21:52:59 »
quote:
Originally posted by gsmollin

The centripetal force is the force accelerating the rock towards you, in the center who are whirling it about you. This force has a magnitude equal to the tension in the string, and a rotating direction that always points at you in the center. Centrifugal force is the reaction force that you feel on the other end of the string, which seems to be pulling the rock away from you. If you let go of the string, the rock flies off in a straight line, since the centripetal force is now zero.



Does that mean that the centripetal force acts on the rock (since it is accelerating toward the center), while the centrifugal force acts on me?  Or does centrifugal force act on the rock also?

Prediction is difficult, especially the future.  -Niels Bohr
 

Offline neilep

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Re: Does centrifugal force actually exist?
« Reply #10 on: 10/08/2005 22:52:44 »
What is the force that made my eggs go over the side of the bowl as I was whisking them too hard ?

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Offline Ultima

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Re: Does centrifugal force actually exist?
« Reply #11 on: 10/08/2005 22:53:27 »
If there was only a force acting on the rock towards the centre it wouldn't stay in a circle, it would just accelerate inwards.

wOw the world spins?
 

Offline neilep

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Re: Does centrifugal force actually exist?
« Reply #12 on: 10/08/2005 22:54:26 »
quote:
Originally posted by Ultima

If there was only a force acting on the rock towards the centre it wouldn't stay in a circle, it would just accelerate inwards.

wOw the world spins?



YEs...but what about my eggs ?

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Offline Ultima

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Re: Does centrifugal force actually exist?
« Reply #13 on: 10/08/2005 22:58:51 »
ukmicky the reason to want artificial gravity (through circular motion) in space isn't just for convenience it's for other health reasons. For long periods with zero gravity you get calcification of the heart because of absorption of bone. Using magnets wouldnít help any of these health issues. Since the magnets don't act on the tissue. Plus when did magnetism have all of these health benefits??? They would need to be fairly strong magnets to act through air at the height of a person. Which means they would likely need a core of some sort which is going to be heavy, and so costly to put into space.

:D The only reason I made the point about centripetal force is because any decent links about it are going to be titled centripetal not centrifugal! If my Physics teacher gets to berate someone for saying centrifugal I should be able to! I spelt it wrong because Iíve never written it down before ;)

wOw the world spins?
« Last Edit: 10/08/2005 23:12:41 by Ultima »
 

Offline neilep

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Re: Does centrifugal force actually exist?
« Reply #14 on: 10/08/2005 23:13:13 »
...well scramble my friggin eggs then  !!..you can't have any of my omelette !!...nyahh nyahh !!

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Offline Ultima

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Re: Does centrifugal force actually exist?
« Reply #15 on: 10/08/2005 23:18:54 »
The reaction against the side of the bowl is what is keeping the eggs in a circular motion. And you are applying a force outwards on the egg with the whisk, so when the bowl isn't there you get egg on your face! :D

I like my eggs.. hatched!

wOw the world spins?
« Last Edit: 10/08/2005 23:19:31 by Ultima »
 

Offline neilep

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Re: Does centrifugal force actually exist?
« Reply #16 on: 10/08/2005 23:21:51 »
quote:
Originally posted by Ultima

The reaction against the side of the bowl is what is keeping the eggs in a circular motion. And you are applying a force outwards on the egg with the whisk, so when the bowl isn't there you get egg on your face! :D

I like my eggs.. hatched!

wOw the world spins?



Thanks Matt !..it's ready...I'll keep it warm for you.:)

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Offline gsmollin

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Re: Does centrifugal force actually exist?
« Reply #17 on: 11/08/2005 02:14:13 »
quote:
Originally posted by Ultima

If there was only a force acting on the rock towards the centre it wouldn't stay in a circle, it would just accelerate inwards.

wOw the world spins?



Yo, Ultima, the rock IS accelerating inward. But since the acceleration vector is always in a direction perpendicular to the velocity vector, all it does is change the direction of the velocity vector from a straight line to uniform circular motion. Also, the work is zero. I'm gonna tell your physics teacher to bitch-slap you anyway.

"F = ma, E = mc^2, and you can't push a string."
 

Offline ukmicky

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Re: Does centrifugal force actually exist?
« Reply #18 on: 11/08/2005 03:11:25 »
originally posted by Ultima
ukmicky the reason to want artificial gravity (through circular motion) in space isn't just for convenience it's for other health reasons. For long periods with zero gravity you get calcification of the heart because of absorption of bone. Using magnets wouldnít help any of these health issues. Since the magnets don't act on the tissue. Plus when did magnetism have all of these health benefits??? They would need to be fairly strong magnets to act through air at the height of a person. Which means they would likely need a core of some sort which is going to be heavy, and so costly to put into space.

 The only reason I made the point about centripetal force is because any decent links about it are going to be titled centripetal not centrifugal! If my Physics teacher gets to berate someone for saying centrifugal I should be able to! I spelt it wrong because Iíve never written it down before

------------------------------------
If the electro magnets were placed in the floors and the spacesuit was made with metallic rings or plates sewn in, in order for the person to stand up and counteract the magnetic force pulling them to the floor they would have to use their bones muscles, wouldnt that give the same effect as gravity on bones etc.

Yes it would be heavy and expensive but not as heavy and expensive as a giant centrifuge, and it would only be needed in some areas of the ship like the living quarters.

In my job I regularly have to visit a company that sells magnetic healing aids. Itís a proper company selling world wide. A lot of their trade is through referrals from the UK and US medical professions. I have no reason not to believe their claims.
I go by what they tell me. But I will check it out incase what they tell me is a load of baloney.

 It didnít matter that you spelt it wrong. But for some reason I just had to point it out:).

« Last Edit: 11/08/2005 04:27:05 by ukmicky »
 

Offline gsmollin

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Re: Does centrifugal force actually exist?
« Reply #19 on: 11/08/2005 10:49:54 »
What is the name of this company? I used to work for a company making magnetic healing aids. To be precise, they were electro-magnetic healing aids, not magnetic jewelry. I thought the work was promising, but the company went bankrupt after problems selling thir heart pacer. That aside, I always wondered if anybody else was working on EM healing devices.

"F = ma, E = mc^2, and you can't push a string."
 

Offline Ultima

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Re: Does centrifugal force actually exist?
« Reply #20 on: 11/08/2005 14:37:58 »
The force wouldn't be applied directly on the bone though. So when you are asleep or relaxing there would be no force applied? It would only have an effect on muscles that would be used to move around... what about all the other muscles you have internally! The force isn't being applied directly on the tissue is it. If you used circular motion to apply a force on the body it applies to the actual tissue not just some suit. I don't see how magnetism would aid in healing at all??? What is the magnetic field interacting with inside your body, possibly for problems with nerves etc. I could see how it might work..?

wOw the world spins?
 

Offline gsmollin

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Re: Does centrifugal force actually exist?
« Reply #21 on: 11/08/2005 16:11:47 »
The device I am referring to used a pulsed magnetic field to induce eddy currents in the body tissues. The currents were larger in the vicinity of a broken bone than in healthy tissue. The electric current flowing across the broken bone sped up the healing process. In geriatric patients, the results were rather impressive, with bones healing in a few weeks that had not healed in a few years.

"F = ma, E = mc^2, and you can't push a string."
 

Offline ukmicky

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Re: Does centrifugal force actually exist?
« Reply #22 on: 12/08/2005 03:03:11 »
gsmollin
The company is called dulwich health and are based in  london se19 near crystal palace. They don't manufacture what they sell, they are just a source for people needing advice and products to do with  complementary and alternative Therapies.
I used to think anything to do with alternative medicine  was a big con, then i saw there office walls which are covered with hundreds of letters from people thanking them.
 
« Last Edit: 13/08/2005 01:10:29 by ukmicky »
 

lyner

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Re: Does centrifugal force actually exist?
« Reply #23 on: 25/12/2006 00:01:52 »

Centrifugal force is quite a valid concept.
Newton's Third law of motion says that for every action there is an equal and opposite reaction.
To move in a curve, you need a force towards the centre. This is a Centripetal force but there must be an equal and opposite force (say on the string of a conker as you swing it) which is directed away from the centre - a centrifugal force. BUT, as soon as you cut the string to remove the centripetal force, the centrifugal, reaction force will disappear. This is similar to the force upwards on your backside as you are sitting in the chair. The force disappears as soon as you get up - it can't throw you up into the air.

If you are ON a spinning object (a spinning frame of reference) you will experience two forces. The centrifugal force will 'feel' as if it is throwing you outwards and if you drop an object it will appear  TO YOU to go outwards. A stationary observer will see this object leave your spinning frame on a tangent. It is not thrown out- it will keep moving in the direction in which it was moving when you let it go (in that observers frame). But to you, it has been thrown out and will travel in a curve!
Coriolis force is a wierd one; it is only experienced if you try to move and   you will be 'thrown sideways' as you move towards or away from the axis of rotation. As you move away from the centre your tangential speed is less than that of the place you are moving to (it is moving with the same angular velocity as you but its radius is greater). You will have the impression of being pushed to one side as you move towards the place you want to go to. This is why, when air flows from high pressure areas to low pressure areas, on the Earth's surface, it goes in circles to cause hurricains, depressions and tornadoes.
Sit on a child's playground roundabout or spin on an office chair to experience both forces - it is the Coriolis force that is the really disturbing one.
I have a feeling that Physics teachers ban the concept of centrifugal force because they don't feel confident to give (or improve on) the above explanation.
'Real' physicists are quite happy with it.
 

lyner

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Re: Does centrifugal force actually exist?
« Reply #24 on: 25/12/2006 00:10:47 »
'Artificial gravity' using magnets on your shoes wouldn't help your muscles keep in shape. You would just have to pull your feet away from the floor to walk, rather than support the weight of your body on your leg / spinal muscles. We  'just' have to wait for a propulsion method that produces almost g acceleration for weeks on end! We could then travel within the solar system, at least, in comfort. Not sure about the energy source for this.
 

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Re: Does centrifugal force actually exist?
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