email question on collision domains (q1)

email question:

The notes say "Switches isolate potental collisions by removing collision domains (areas where collisions occur, where they shouldn’t)", so does this mean that when there is a switch there is no collision? 

answer:

     Switch 'may' have collisions, but it is exponentially unlikely, assume you use all switches.   The reason being, ethernet is a shared medium (more than 1 computer can share the wire).    Now, if you ONLY have 1 computer per switch port (and no hubs), you would VERY RARELY have collisions (only if both switches sent at the exact same time).  If a switch is connected to shared ethernet cable, all computers in that shared ethernet cable can collide with each other, as the switch can not partition the computers on a shared medium (shared medium is the same as a hub, tying all the computers together).