What is the primary cause of rolling resistance?

[kamaljeet_pec]

In solids there are crests and troughs. In highly polished surfaces there are molecular forces. But what creates friction during rolling where there is only line contact (in case of cylinder) or point contact (inn case of a ring)?

I read somewhere that when an object is rolling it forms a hump in front of it on the surface on which it is rolling. Thats what opposes it and hence is a cause of friction. I don't really buy that.

Please help me understand.

 

[chrisbaird]

When an object is rolling and not slipping, the point of contact is static, therefore the friction is static friction. It is the same thing that keeps a block of wood from sliding down a rubber ramp. Static friction is due to surface roughness as well as an electromagnetic attraction of the molecules in both surfaces when close together because of slight induced charge dipoles (the Van der Waals force). Geckos can stick to sheer vertical surfaces because their fingers have pads that optimize the Van der Waals force.

 

[rcgldr]

I read somewhere that when an object is rolling it forms a hump in front of it on the surface on which it is rolling. Thats what opposes it and hence is a cause of friction. I don't really buy that.

The opposition to rolling is called rolling resistance. From a wiki article:

The primary cause of rolling resistance is hysteresis

http://en.wikipedia.org/wiki/Rolling_resistance