Given that, Work = Force × Displacement, the unit of force in SI system is newton (N), while the unit of displacement is metre (m). Hence, the unit of force is newton-metre, also called joule. If a force of 1 newton displaces an object through 1 metre in the direction of the force, the amount of work done on the object is 1 joule.
1 joule = 1 newton × 1 metre. Therefore 1J = 1 N × 1m.
Alternately, the unit of force In CGS system is dyne, while that of displacement is a centimetre (cm). So, the unit of work done is dyne-centimetre, also called an erg.
Now, If a force of 1 dyne displaces an object through 1 centimetre in the direction of the force, the amount of work done is 1 erg. That is, 1 erg = 1 dyne × 1 cm.