Relativity is generally invoked in lofty thought experiments often involving fast-moving spacecraft, but new work shows that it also applies to the everyday automobile.

Cars are started using lead–acid batteries, which generate energy using electrochemical reactions between lead compounds and sulphuric acid. Rajeev Ahuja of Uppsala University in Sweden and his colleagues modelled the reactions and found that as electrons move at high speed around a lead nucleus, their energy levels change owing to relativity. The authors conclude that the change accounts for 1.7–1.8 volts of a standard 2.13-volt lead–acid cell.

Phys. Rev. Lett. 106, 018301 (2011)