**Before you close this has a duplicate !**

I've read some the related posts on this – but I have slightly different question.

A lot of posts on stack exchange have demonstrated that Newton's laws can be derived / or proved

(A couple of posts have shown that you could derive the 3rd law and potentially the first from the 2nd).

But the 2nd is almost always referred to as an axiomiatic law – i.e. something that is believed to be true – on who's foundation Newtonian mechanics is built.

I'm aware that it has been experimentally proved – in school laboratories countless times (at small scales) etc,.

But – do we have any understanding of WHY this law holds? Is this something fundamental about the universe that it tells us or is the best explanation that it is an approximation of relativistic mechancics at sub-speed of light time frames.

**So my question is:**

"Why are Newton's Laws true – what does it tell us about space, time and matter – and is there any way to develop any more fundamental "laws" that are grounded in more "lower level" axioms. For example – Euclidean Geometry is built on a relatively small set – 5 of axioms – that most of us would intuitively believe to hold true on a plane http://en.wikipedia.org/wiki/Euclidean_geometry#Axioms " – are there any similar axioms that could underpin Newtonian (or indeed Lagrangian / Hamiltonian) Dynamics.

## Best Answer

Physical "laws" are mathematical models intended to reproduce, to some level of accuracy, the quantitative and/or qualitative behavior of a real system or systems.

But physical "laws" are just models. The rules underpinning the model are

chosenspecifically to reproduce the desired behavior. Other rules are rejected because they do not reproduce the desired behavior in the model.As it happens we use mathematics to do the modeling. As it happens that has worked so far and we have refined our theories as best we can using this approach.

In a sense Newton's laws are true in that they reproduce the behavior of many real world systems to within a reasonable accuracy.

In a sense they are also not true, because they do not reproduce behaviors of real world objects accurately enough in all situations.

Similar statements could be made for all the current theoretical models we use. It would be nice to think that there is a single model of the way everything in the universe operates that has unlimited accuracy. But we don't know of such a model and we have no guarantee that such a model is possible.