Joules

Joules are the SI unit for energy. They were named after James Prescott Joule for his work on thermal energy and use the capital letter J. One joule represents one kg·m²/s². The formulae for different types of energy include different variables, however, they can all result in energy being measured in joules (kg·m²/s²).

For example, the formula for potential energy is E_P = m g h and this results in joules by the following logic:

E_P = mass x gravity x height

E_P = 10 kg x 9.8 m/s² x 20 m (SI units)

E_P = 1960 kg m^s/s²

E_P = 1960 J

Another example, the formula for kinetic energy is E_K = 1/2 m v² and this results in joules by the following logic:

E_K = 1/2 x mass x velocity²

E_K = 1/2 x 300 kg x (40 m/s)² (SI units)

E_K = 1/2 x 300 kg x (40 m/s)²

E_K = 240 000 kg m^s/s²

E_K = 240 000 J