[stan_rogers]

You can get quite a distance if you start with electostatics, like charges repel, opposite charges attract, which can be demonstrated with simple apparatus.

That really only answers the "what", though; it doesn't touch on the "why".

We can describe the attraction and repulsion, throw a precise mathematical framework around it, describe how two or more things might just be different aspects of (or viewpoints on) the same underlying phenomenon, even put names and behaviours to the particle-like things involved, but when it comes right down to it, nobody knows why any of it should result in forces that tend to move physical things closer together or further apart.

And that's okay, but it does mean drawing a line somewhere and saying "this is fundamental (at least for now)".