“The no-slip condition makes trouble—if subtle trouble—in our everyday lives. One swipe of a dishcloth works as well as lot of flowing hot water. The dishcloth contacts the dish, sweeping away surface mess; the flowing water doesn’t make such effective contact. Hot water works better than cold, not just because more substances dissolve in hot water, but because hot water has a much lower viscosity; that means more fluid moves close to the dish. Dust accumulates on the surfaces of fan blades; the low flow right near a blade’s surface isn’t enough to dislodge it.”