im trying to mechanically show it using a string..nothing to do with my arms moving..
i got to design a piece of equipment that will contain a string showing a standing wave..
I've never done it with a string. I think that very light strings are harder to work with because they have little mass. The surrounding air may act as a dampener and make it more difficult for a reflected wave to sustain itself. You could try I guess but I have had good luck with using a long thin rope that had a little heft to it. Tie one end off on the end of a table and just wave your arm up and down.
It should be possible to construct a simple version of Melde's experiment using a small electric motor, a string, a pulley and some weights. http://en.wikipedia.org/wiki/Melde's_experiment
http://www.practicalphysics.org/go/Experiment_129.html
Glue popsicle sticks to the string at the center of the stick all the way along the string side by side. Slightly weigh down the bottom of each stick with anything. Attach the string at both sides.
Now all you need to do is turn the first stick to 90 degrees and let go, then watch the standing wave from the top. Standing wave from a string... and sticks.