Question

why and how is there space between 2 objects even when they are in contact ?How does this force work?

Answer 1

The surface may be smooth to our eye. But it is still not smoother surface in micro /atomic level. So definitely there will be some space in between them even it is in contact.
The surface of an object at the atomic level is a cloud of electrons being held by an array of nuclei, and the electrons have a probability distribution determined by a wave equation. There is no sharp surface, but rather an ever-decreasing electron density as we observe further from the nuclei.
What happems when two such surfaces approach each other? Think of the two surfaces coming closer, and there is some electron repulsion, but the electron distribution cannot change very much because the energy is determined by the wavelength of the waves, and that energy is about two orders of magnitude greater than these initial interactions. Indeed, at first there is an attraction between the two bodies, for two reasons. The first is the nuclei see an electron density of approximately twice what is expected in that direction, so they tend to move slightly closer to this increased density. There is also the Casimir force. So, all these forces, integrated over the surface area of the objects, gives a net attraction, although if the objects are pushed even closer (and that attraction is over an extremely small distance range) the electron-electron repulsion predominates.