jzz said:
it is gravitational forces that are responsible for friction
Not necessarily. There has to be
some normal force in order for there to be a friction force, yes. But the normal force doesn't have to be provided by gravity.
jzz said:
A look at the events in the International Space Station where gravity is at a minimum, shows that objects don’t even stay put in one place, they tend to float, let alone experience friction.
An object
will experience friction if you, for example, push it up against the wall of the station and then try to slide it along the wall. In other words, if you provide a normal force pushing the object into the wall.
jzz said:
at some point electrostatic forces must also take part
Of course. The forces causing atoms to repel each other at short enough distances are electrostatic.
jzz said:
gravity is 10^40 (approx.) times weaker that the electrostatic force
More precisely, gravity
between two electrically charged particles like electrons is about ##10^{40}## times weaker than the electrostatic force
between the same two particles.
But for macroscopic objects, the force balance is very different. The objects as a whole are electrically neutral, because positive and negative charges are present in equal numbers and so cancel each other out, so there is
no electrostatic force between them as bulk objects; there is only the very short-range repulsion between their atoms when you try to push them together. But gravity does not cancel out; there is no gravitational counterpart to positive and negative charges, there is just positive mass. So gravity just keeps piling up the more and more mass is present.
jzz said:
The massive size of the earth in comparison to everything else might have something to do with it.
That is what makes the Earth's gravity easily perceptible to us, yes. But with very sensitive instruments we can detect the gravity of much smaller objects (look up the Cavendish experiment and more recent elaborations of it).
