Joule's law in thermodynamics

When two palms are rubbed with the fastest manner, then suddenly heat is generated, so we can't continue this process further because we can't bare it.
we have done some work i.e., rubbing the two palms, so that works turns into heat. From this example, we conclude the equivalence of mechanical work to heat. That relation is formulated by Joule. He says that the mechanical work is done on the system then proportional heat is produced from the system.
Therefore, the mechanical work W on the system is proportional to the heat produced Q from the system, i.e.,
In order to produce unit quantity of heat, mechanical work done is W=product of (J,1) where Q=1calory
then Joule's constant J=4.18joule/calory, since 1joule=4.18calory, from this we have derived the value of Joule's constant.