If classical physics laws fail at the quantum level , why do we still use classical physics formulas for deriving relations at an subatomic level ?

Question

While getting a lecture on drift velocity of electrons , i came across the formula F=MA being used for electrons .

also equations of motions were applied to subatomic particles .

but if classical physics formulas fail at quantum level , why do we still use them in quantum physics ?

Answer 1

The math does not change and the basic physical laws still hold. On the basic level, F still equals to mass multiplied by the acceleration. There are fine adjustments that take place and change the effects and these we do not see in the macro world.

 

Note, that there are also two other forces we do not see interacting in the macro world, like weak force and strong force. These still obey the above law. This is the starting point of all observations.