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).he joule (/ˈdʒuːl/), symbol J, is a derived unit of energy in the International System of Units.