The particles that make up a rock are constantly in motion however a rock does not visibly vibrate. why do you think this?

I think this is because the particles don't know or care about each other,

and they act completely without any peer pressure. The direction in which

any one particle vibrates is completely random, and there is no connection

or influence among the particles. That means that any direction is just as likely

as any other direction for the next vibration, and they all wind up vibrating in

different directions. There is a tiny tiny tiny tiny chance that all of them could

vibrate in the same direction for just an instant; if that ever happened, the rock

would suddenly jump up in the air. That's actually true, but the chance is so tiny

that it hasn't ever happened yet. In fact, the chance is so tiny, that when scientists

do their calculations of particle vibrations, they assume that the chance is zero,

and that makes the calculations simpler.