in mechanics and physics we are forever talking about friction and using it to solve problems. but what actually is friction? is it as simple as saying how rough a surface is? that doesn't sound adequate to me. if that were the case then i'd expect all materials to have the same coefficient of friction if they were as flat as a mirror for example. i have a feeling that it probably has something to do with interactions between electrons on the surfaces of the two materials in contact. please can somebody describe the actual reason we feel a friction force. thanks.