Friction, tribology, and the complex art and science of lubrication
Back when whale oil was mainly used as a fuel to burn in lanterns and streetlights, an enterprising man named William F. Nye found a new way to sell whale oil to a rapidly changing world: as a lubricant for all the new fangled machines. Nye specialized in specialization- selling different oils for watches, sewing machines, bicycles. Lubrication has had a largely invisible role in the design of the modern world, but its importance cannot be overstated.