Where there is high-speed rotation in the engine, e.g. with a plain bearing, the high speed draws a thick layer of oil between the two surfaces, like a wedge. Here, this oil supports and carries the load of these surfaces. As soon as the spinning stops, however, either due to the slowing down or stopping of the engine, this wedged oil gives way. Where no rotation occurs in an engine, oil cannot form this thick wedged layer to protect metal surfaces. Here, oil provides a thin protective film and often relies on anti-wear agents, detergents, and anti-oxidant chemicals to help protect from metal-to-metal contact.