Monday, June 2, 2008

Friction - Devil or God!?

Everywhere you see, one is attempting to reduce Friction. E.g. the lubricating oils in ball bearings, door hinges. However, have you thought about what would happen if there was no Friction!
Without Friction, you can't even walk on the floor! That's what happens, in rain, if the floor is slippery, you tend to fall down. Why, because the Friction has got reduced. Its a strange thing that the force of Friction, which opposes every motion, is actually supporting the entire mechanism of motion!
Let's say you want to walk. Now suppose you were in Space, then unless someone gave you a push, you wouldn't move from where you are! So when you walk, what you do is you push back on the ground. The only way you can push something is when you have some grip over it. That's Friction. Without Friction, when you attempt to walk, you will actually roll over and fall!
When a wheel moves on the floor, three things can happen: It can slide like a sledge- this happens when your wheels are break locked and there is no rotation of wheel, or It can rotate without any translation, as it happens when a wheel is stuck in a ditch of mud, and any amount of acceleration only gives it rotation, no translation. Third thing which is expected, normal behaviour, is rotation and translation. This can happen only when there is adequate Friction.
What is Friction. On a microscopic level, the smooth looking surface is not a regular plane. There are hills and valleys at atomic level. Whenever two surfaces meet, they form temporary contacts, and molecules of one surface invade in hills and valleys of other surface. They interlock and push each other. So if a top surface is moving forward on a bottom surface, the bottom surface pushes the top one back, and the top surface pulls the bottom one forward.
This is easily seen in case of liquids. The analog of Friction is Viscocity. An Oil is more viscous than water and Honey is more viscous than Oil. In a mixer, when the blade rotates, it carries along with it the layer of liquid next to it, and that layer drags the next layer with it and so on, the subsequent liquids are set in motion. Had there been no Viscocity, you wouldn't be able to stir your coffee!


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