Consider a tube with both ends closed (or a
string with both ends "locked down") .. we can see the evolution
of the standing wave as time goes on. We can select different frequencies
of the oscillation (fundamental and then several harmonics).
The top curve shows the initial wave, the middle curve shows the "reflected" wave returning, and the bottom shows the combined waves thus, what the pressure wave (string shape) would actually be.
Observe : with a closed end on the right, watch what happens when the first edge of the wave reaches it .. the wave reflects back "upside down" - inverted - compare that to the simulation with both ends open, where the returning wave comes back "on top".
Credits: Mostly created by Ali Loewy and Andrew Duffy at Boston University - modified partially by Scott Schneider.