8bf0eb34_PMM_physics__About_friction__Type
[...and something about it] Whenever a sledge is pulled over the ground or a sliding bearing in machinery is applied, two material surfaces rub on each other. As surfaces are not perfectly smooth, the work needed to overcome the friction is transformed into heat, which can be very high, e.g. when metal tools are ground on a stone. This type of friction can be reduced, but not eliminated by applying a suitable type of oil or grease to the sliding surfaces. Air cushions or the repelling effect of magnets can also reduce sliding friction. But keep in mind that in all these cases, one type of frictional behaviour is replaced by another type which also must be taken into account. [Type] 
sliding friction
s l i d i n g f r i c t i o n
r o l l i n g f r i c t i o n
e l a s t i c d e f o r m a t i o n
p l a s t i c / i n e l a s t i c d e f o r m a t i o n
l i q u i d f r i c t i o n
e l e c t r o m a g n e t i c f r i c t i o n
t i d a l f r i c t i o n
s o u n d
PMM physics. About friction
Type