We have two setups for generating standing waves. Two people
can swing the long spring. Make it two physicists who know
what type of wave pattern they want and they can generate
a standing wave with 2, 3, 4, perhaps 5 nodes. The nodes are separated by 
which therefore takes on values
Since 
the corresponding ``resonance'' frequencies are
We also have a setup which can induce such standing waves by
exciting a string which is kept taut by hanging a mass from one end.