Ethernet segments,csmd/cd,

I was wondering if somebody could clear up questions about Ethernet, Ethernet segments, csmd/cd and switched Ethernet networks.

1. Is Ethernet a protocol therefore fitting into the data link layer of the OSI model or does it fall into the Physical Layer.
2. Would a connection between two nodes on a network be considered a physical Ethernet segment.
3. In a switched Ethernet environment are there collisions in the switch.
We seem to be having a debate and would really like some clarification.

Thanks