surface tension circle
Form a loop from a 6 inch length of thread by overlapping
the ends about 1 inch. Float the loop on the surface of water
in some container. Touch the surface of the water within the
loop with a bar of soap or with a toothpick end that has been
pushed into a bar of soap. The loop will be pulled into an
impressively perfect circle.
The same effect results when the thread ends of the loop are
tied and the loop is placed on the soap film of a bubble
blower. Poke the film within the loop with a pencil point to
break it.