Newton's second law, for example, states that $F=ma$. Is this absolutely true, down to the smallest possible unit of measurement? Or is it just a handy approximation that happens to work extremely well for everyday sized objects/forces?
Suppose I have some arbitrarily precise measuring devices capable of taking measurements down to the Planck length/second/force. And I set up an experiment where I apply a force to an object to test its acceleration, removing all outside interference. Would $F=ma$ hold true?