there be a node at an open end
there's a node at a closed
end because the air can't move there (in the pipe, air only moves longitudinally
, of course)
be nodes in the middle
of the pipe, but only because of interference from reflection from both ends
at the open end, there's nothing on the "outside" side to reflect from
, so no interference and no node!
(and if there's a standing wave, the end must be either a node or an anti-node, so in this case, it's an anti-node)
btw, the anti-node is actually just outside the open end … you need to apply an "end correction"
for details, see my favourite sound site, http://www.phys.unsw.edu.au/jw/flute...nets.html#time