Superposition on longitudinal wave

[Kai]

When a spring is fixed at both ends and it is vibrating back and forth, reflection will occur. So where are the nodes and antinodes? Are they at compression or rarefaction region?

 

[haruspex]

When a spring is fixed at both ends and it is vibrating back and forth, reflection will occur. So where are the nodes and antinodes? Are they at compression or rarefaction region?

A node is where there is little or no displacement during a cycle, an antinode where the maximum displacement at that point is the maximum of anywhere. Since the ends are fixed, they will be ... which?
This is sort of opposite to compression and rarefaction. Compression and rarefaction regions can be found at some snapshot of the cycle, but over the course of a cycle they are the same places: maximum compression in one half of the cycle occurs where maximum rarefaction occurs in the other half.
These are maximised where displacement is minimised, and vice versa.