a) not sure, did not have personal experience with them myself
b) Your misunderstanding comes from thinking that this plane that we inhabit is the only one, and that if stuff happens, it has to happen physically.
If a poltergeist is created, it is embedded in a field/plain/dimension above ours, the mental plane or however you want to call it.
The point is, just like with telekinesis(again, doable, but dont come here with doubt unless you tried doing it for at least three months), it does not work with the physical laws. The only way to influence that, is to make it move in a higher plane, the mental plane, this way, if energy is sufficient, it will start manifesting in the lower plane, aka the material.