Are Newton's laws invalid in real life?

Question

One of my friends and I had an argument over this topic. He stressed the fact that in real life many forces exist, whereas in physics we deal only with ideal situations. He put the following arguments:- >1. Newton's First Law is invalid because friction exists in real life. >2. Newton's second law is invalid due to the same reasons. >3. Newton's third law is invalid because in a trampoline, there is excessive reaction. In defence, I put forward the following arguments:- >Newton's laws are true but the equations have to be modified to take into account the other forces in real life. >For example, if a force $F$ is applied on a body of mass $m$, and $f_s$ is the force of friction, then, the equation becomes $F - f_s = ma$. Thus, we have just modified the equation $F = ma$. >So basically I mean to say that we have to adjust the laws to suit our purpose. In the end, there was a stalemate between us. Even now I am confused after this argument. Please clarify my doubt.

Answer 1

 Hello! To answer your question, the laws are absolutely NOT "invalid," just because the world is much more complex than the equations you learn in early physics. You and your friend are both a little wrong, and you're both a little right. IF you take Newton's Laws in their most basic forms (as they're presented in high school physics, for example), then yes, it would be impossible to get "correct" or exact answers by just plugging in real-life numbers to the simple equations. You'd get approximations. However, what you do when you adjust for things like friction, is not modifying the LAWS themselves, but rather applying the SAME LAWS with MORE VARIABLES. So in no way are you invalidating them, you're just taking into account the true complexity, which was simplified a bit in your physics textbook for you anyways. Hope that helps.