# Friction in a vacuum?

Discussion in 'Physics' started by tjohnson, Jan 29, 2015.

1. ### tjohnson Thread Starter Active Member

Dec 23, 2014
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I have wondered for a while whether or not friction exists in a vacuum. Obviously air resistance, one of the primary types of friction, would not exist, because there is no air in a vacuum. Although since it's impossible to create a 100% perfect vacuum, I suppose there would always be a slight amount of air resistance.

Thinking purely theoretically, if a perfect vacuum could be created, it would have no friction, and perhaps a perpetual motion machine could be operated within it. But even if so, it would be utterly useless as an energy source, because it would have to be connected to the outside world in order for energy to be transferred from it and thus would lose its vacuum properties.

My curiosity led me to do an Internet search about friction in a vacuum, which led me to http://www.newscientist.com/article/mg20927994.100-vacuum-has-friction-after-all.html. That webpage, as well as several others, mentioned two Spanish scientists who claim to have discovered that there is actually a small amount of friction that exists in a vacuum.

2. ### WBahn Moderator

Mar 31, 2012
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Doesn't matter whether there is friction or not -- as soon as you draw energy from it, you are drawing energy from it and its motion is no longer perpetual.

As for friction in a vacuum, the term "friction" encompasses a lot more than just air resistance. If friction didn't exist in a vacuum, then the astronauts would have had a very hard time walking on the moon, would they not? Or working on the outside of the ISS? Or countless other operations.

The nature of the friction between two surfaces is impacted by the presence or absence of an atmosphere, among other things.

tjohnson likes this.

Jan 18, 2008
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Dec 23, 2014
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5. ### WBahn Moderator

Mar 31, 2012
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I think your query is reasonable and within bounds (but, then again, I'm not a mod).

I think that discussions about what perpetual motion and over-unity machines are and what the limitations are on them is fine, as long as it doesn't stray into the claims of having one or how to make one (but, then again, I'm not a mod).

6. ### Wendy Moderator

Mar 24, 2008
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I don't think anyone has trouble discussing physics here.

Even orbits are not eternal. The moon drifts out about an inch a year due to the tides.

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7. ### studiot AAC Fanatic!

Nov 9, 2007
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I think that you need to distinguish between air resistance and the friction generated as the product of the coefficient of friction and a normal reaction force, which are entirely different effects.

Reading through this thread I assume you only mean the drag forces exerted by a fluid on a body moving through.

However other drag type effects can also exist in a vacuum.

Electrostatic, magnetic and gravitational forces can all extert drag on an object moving in a vacuum, thereby extracting energy from it.

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8. ### wayneh Expert

Sep 9, 2010
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And even empty space is not entirely empty. An object moving through space will experience drag due to all those fields and due to an occasional impact with stray atoms, and even with solar winds.

That said, a spinning wheel in space would spin a very long time, appearing nearly "perpetual" to an impatient observer.

9. ### BR-549 Distinguished Member

Sep 22, 2013
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It will depend on how you define friction.

Particles...have been spinning since the beginning.

However....when particles combine and form matter.......then gravity takes effect.

Gravity is the only thing that is changing. It is slowly decaying.

This is the cause of entropy.

So all matter will expand and slow down.

But not because of friction......because of gravity.

10. ### #12 Expert

Nov 30, 2010
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Air is only one cause of friction. All the other causes exist* in a vacuum. *(I would say, "unchanged" but somebody would surely think of an exception.)

Getting energy into and out of a vacuum chamber is relatively easy. Electrically, you can use glass as a melt-able insulator around metal rods. Mechanically, they are called, "shaft seals". These work because Earth only has 14.7 P.S.I. trying to get into the vacuum chamber and a tiny layer of oil will finish perfecting the seal. Thermally is another matter. A vacuum is a pretty good thermal insulator, but increases conduction of electrons, as in radio vacuum tubes. Still, getting an electron stream in or out of a vacuum chamber without a metallic conductor exceeds my imagination. If the vacuum chamber is made of clear glass, light will go in and out easily.

11. ### Rolland B. Heiss Member

Feb 4, 2015
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That's interesting to me! How do the tides so far away cause an object, in this case the moon, to drift a whole inch when the moon happens to be over 200,000 miles away depending upon the season?

12. ### WBahn Moderator

Mar 31, 2012
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If the moon can affect the tides, then the tides can affect the moon (equal and opposite, remember?). Gravity works both ways -- and at unlimited distances. The sun affects Pluto and Pluto affects the sun. Distant galaxies affect us and we affect them.

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13. ### Rolland B. Heiss Member

Feb 4, 2015
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True. Seems so simple and yet I can't help wondering if there is something humankind has been missing in relation to all of this which is yet to be discovered and understood. After all, according to Michio Kaku we are a mere type 0 civilization close to attaining type 1.

14. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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Really? I for one would like to see proof of this. Preferably, rigorous.

15. ### nsaspook AAC Fanatic!

Aug 27, 2009
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I would take what Dr. Kaku says with a grain of salt.

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16. ### Rolland B. Heiss Member

Feb 4, 2015
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Hehehe... yeah, sometimes I wonder about him. However, what could one accomplish with a grain of sodium chloride and a few other things coupled with ideas apart from making a simple battery in a minute and a half?

17. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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...a lime, and a shot of tequila.

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19. ### nsaspook AAC Fanatic!

Aug 27, 2009
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Dr. Kookoo just doesn't know when to stop his mouth.
You should never be so open-minded that your brain falls out.
http://scienceblogs.com/principles/2010/06/23/the-physics-of-the-imbecile/

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