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My teacher said that if surface is smooth coefficient of friction is low but if it gets very very smooth coefficient of friction starts increasing

I didn't get why?

Utkarsh futous
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  • Two very smooth surfaces may try and actually join together if they are the right material. See http://physics.stackexchange.com/questions/15876/why-making-a-surface-super-smooth-increases-the-coefficient-of-friction?rq=1 http://physics.stackexchange.com/questions/11543/what-happens-when-two-smooth-surfaces-touch and probably some others in the related secti0n. – JMac Mar 30 '17 at 13:16

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It depends on the type of friction too. Rolling friction vs sliding, static vs kinetic friction. Static friction has been attributed to an actual sharing of electrons between the materials even if they are not conductive. The smoother the surface the more electrons can come in contact and interact with other atoms between the materials.

There is also the vacuum effect, if the two surfaces are very smooth then when they come in contact the air can be pushed leaving you with a vacuum or very low pressure between when you try to remove the 2 parts.

There are some very informative videos on this concept of very smooth contact between steel gauge blocks. Read the section in the wikipedia link below on wringing gauge blocks and search for some videos.

https://en.wikipedia.org/wiki/Gauge_block

Drew K

Gwydionforge
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