The joule (/ˈdʒuːl/), symbol J, is a derived unit of energy in the International System of Units. It is equal to the energy transferred (or work done) to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N·m).ne joule can also be defined as: 1  The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one 'coulomb volt (C·V). 2  This relationship can be used to define the volt.