Why do soap bubbles have many colors? Why do they sometimes swirl?
Rainbowing of any sort is caused by the differential refraction
of light waves, breaking the light into its component parts
which we call colors.
In the question you asked about rainbowing on the bottom of a
stainless steel pot, the rainbowing you see is due to different thickness
is of oxide taking the light in your environment and breaking it
into its component colors depending on the thickness of the
oxide in the various areas.
With the soap bubbles, the different thickness' of the soap film
forming the bubble will also separate the light differently
depending on the soap film thickness. The reason you see the
swirling is that, as you blow on the bubble, or as air hits it,
the areas of thicker/thinner soap film thickness move on
the surface of the bubble, and you see the light reflected off the
bubble changing according to the diffraction caused by the
changing soap film thickness.
I hope this answer is clear to you. Please write to me, or ask
your teacher or parents if you need further explanation.
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Update: June 2012