# When does water decrease or increase friction?

Water often acts as a lubricant e.g. a wet floor or road, but sometimes the reverse happens e.g. putting on wet clothes. I understand that surface tension is involved e.g. microscope slides sticking together, but are there other factors?

What determines which effect dominates?

• I don't know that this is well understood. There is a discussion in Blau, Friction science and technology, p. 195. As an example, friction of nylon on steel is reduced by wetting from $\mu_s=.35$ to .22, but for nylon on nylon wetting raises $\mu_s$ from .41 to .51. Data quoted by Blau from Bartenev and Lavrentev, Friction and wear of polymers, Elsevier, 1981. This kind of thing is infamously hard to measure reproducibly. You have to prepare and clean the surfaces. Wearing in matters, and the behavior as a function of wearing-in time can be complicated.
– user4552
Sep 9 '19 at 14:06