# Thread: Friction

1. What actually is the scientific fact on which friction depends.

eg:- If a marble is slid over a surface it travels a large area where as if a wooden roll is slid it travels a less area. Similar is the case with sand and soil.

2.

3. Structure and resitance.

Try goolging it.

4. NO don't try googling it - YOU try googling it!

If you are going to suggest a 'google' at least spell it properly, give the poor sod a chance!

Or you could just think about it on a micro-scale

And if that does not work take your dad's 4*4 out and push it along a flat highway = then do it over bumbpy ground - imagine this at a near molecular level and you have friction.

IN simple terms the rougher the surface(s) the more the little bumps crash into each other - glass has a very smooth surface bricks are rougher. - when it comes to lubrication - the oil is like tiny 'balls' which allow the surfaces to 'roll' past each other.

5. As I read once in a Physics book that friction in caused by the attraction force between the atoms of the bodies.

But in fact I did not get why this attraction happens only between (((some bodies))), what is special about them????

6. Casmir effect ? (Initially)

But eventually no. As you put two pieces of whatever together there will be a slight repulsion between electrons. Good job really, as matter is mainly insubstatial if this were not the case we could probably walk through walls.

7. ok whatever there are many factors and even many aspects ro look at.
I would try it to find it in more detail somewhere.
Thanks

8. There are simply two ways to look at it, I have given you the classical view explained in fairly simple terms - others appear to have tried to take it to the level of 'quantum physics' - if it is the later answer I would urge you to probe further.

9. I have studied in kinetics that when some work is done on any body it gains potential energy which is then converted into kinetic energy and when whole of p.e. is converted into k.e. it comes to astop due to friction.
If this friction be not there then due to inertia of motion it would go on moving.

And i wanted it's explanation down at the molecular level and might be quantam physics. So it would be great for me if you give some details about it.
Thanks

10. Ehh quantum physics isn't to be taken lightly...

Read it up and let the brain-pain ensue haha

Well it is confusing for me at least because it just all sounds dumb because I can't comprehend the maths behind it.

11. Well i like to read science in detail. Nothing is like trying. Don't give up any time.

12. Actually it is this way-a movng. body has KE.
friction as u know opposes motion.
so in order to overcome friction body uses its energy.i mean it loses some energy to overcome friction force.
due to this its energy decresses.slowly and slowlyit loses all its KE and then it stops
so if there is no friction or any other opposing force body goes on moving

13. Originally Posted by bittu
Actually it is this way-a movng. body has KE.
friction as u know opposes motion.
so in order to overcome friction body uses its energy.i mean it loses some energy to overcome friction force.
due to this its energy decresses.slowly and slowlyit loses all its KE and then it stops
so if there is no friction or any other opposing force body goes on moving
Yes we know all that but I think the original poster was referring to the mechanism of what causes friction. In short, it is the electroweak force.

14. I have never read anything describing friction so I am making my own theory... on all surfaces, they have ridges and depressions. I think that when you rub two things together, the ridges start tearing at each other. its like mountains at a molecular scale. if a mountain flipped onto another mountain and shifted back and forth, with enough force, they would start to cut into each other and shear. this is what I think happens. if this is an unclear explanation, please tell me.

15. If you look back to my first post in this thread you will see you and I are in broad agreement. Friction is resistance to rolling motion, whether by a rough surface, or other forces, stiction is the tendency of an obect to stay where it is - if you like initial friction.

16. Originally Posted by chamilton333
I have never read anything describing friction so I am making my own theory... on all surfaces, they have ridges and depressions. I think that when you rub two things together, the ridges start tearing at each other. its like mountains at a molecular scale. if a mountain flipped onto another mountain and shifted back and forth, with enough force, they would start to cut into each other and shear. this is what I think happens. if this is an unclear explanation, please tell me.
do u mean like if gears were laid out flat and they put enough lateral force on each other they would shear, and this happens with little groups of atoms?

17. Originally Posted by Menos
do u mean like if gears were laid out flat and they put enough lateral force on each other they would shear, and this happens with little groups of atoms?
yes, except that the atom's rising and falling are irregular as opposed to the regulated elevation of gears.

18. When you force two pieces of sandpaper past each other, some grains are broken and some are worn down, the physical energy is converted to heat, at an atomic level.

19. Originally Posted by Megabrain
the physical energy is converted to heat, at an atomic level.
do you agree that this is the result of the atomic bonds being broken and releasing energy in the form of heat

P.S.-- my new avatar is morton the apple being poked with a peice of silverware

20. I think if anything is 'split' it will be molecules rather than atoms.

21. Originally Posted by Megabrain
I think if anything is 'split' it will be molecules rather than atoms.
either way, it is true that the heat is a result of broken bonds, right?

22. Originally Posted by Menos
Originally Posted by Megabrain
I think if anything is 'split' it will be molecules rather than atoms.
either way, it is true that the heat is a result of broken bonds, right?
No.

Electrons repel each other. When you are rubbing two piesces of material together, as they are rough at the molecular level, some electrons of one piece come closer to the electrons on the other piece, what happens next is that the electrons repel each other. When more force is applied and the two pieces are forced closer together, the repulsion between electrons causes them to jump orbits that are further away from each other. In order to move from an energetic orbit to a lower, less energetic orbit they must loose energy; which they do in the form of a photon; which has infra-red frequency. (Heat)

23. Leo,

Could you provide a source for that?

24. Well are we not distracting from the main topic.
Think there is sand and marble. a piece rolls on sand and retards early whereas on marble it is very late.
I want to what qualities of marble and sand makes them so causing less and more friction.

25. Ah, that's easy!

The sand is 'loose grained' as the ball rolls it displaces some sand either by compressing it or moving it aside, the energy to move each grain is subracted from the kinetic energy of the ball , each time the ball moves a grain of sand it loses some energy, just like a billiard ball striking another the energy is divided between the two.

When the ball is rolled on marble the the marble does not move aside, most of the friction is the ball pushing air out of the way, which again loses energy, this is rolling friction which is different to sliding friction.

26. Thanks it's a nice and easy explantion to understand but do you mean porosity level by loosed grains.

27. porosity is merely the amount of space between the grains, if the sand is packed togetherand 'hard' there will be less rolling friction, if the sand is very porous then more of it will fall into the spaces as it ball rolls ofer it, the more this happens the quiker the ball loses energy.

28. Originally Posted by leohopkins

Electrons repel each other. When you are rubbing two piesces of material together, as they are rough at the molecular level, some electrons of one piece come closer to the electrons on the other piece, what happens next is that the electrons repel each other. When more force is applied and the two pieces are forced closer together, the repulsion between electrons causes them to jump orbits that are further away from each other. In order to move from an energetic orbit to a lower, less energetic orbit they must loose energy; which they do in the form of a photon; which has infra-red frequency. (Heat)
surely that would result in reduced friction? if the electrons are reppelling each other then one result would be a small repulsion force like this <- -> and one of the objects would effectively be floating on the other (if it was light enough

29. Originally Posted by Megabrain
Leo,

Could you provide a source for that?
Other than I cannot think of any other explanation as to why friction would cause heat. Heat is only carried by the infra-red photons. And some mechanism must be involved in the creation of such photons. My theory seems the most reasonable. Unless anyone has a better idea ?

30. I didn't think you could... :wink:

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