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What would be the interest of bathing without bubbles? They smell
good, they sound funny and they want to be played with. But how
do they exist? First of all, bath bubbles are made of soap, air
and water. When you pour bubble bath into the tub, you have soap
and water. When filling the tub with hot water, the air trapped
between the tap and the bath surface is moved underwater. You now
have all three ingredients.
Then, what is soap? Soap is a big molecule, composed of
two parts, one likes water, the other doesn't.
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When gently mixed with water, soap molecules gather on
the surface so that the hydrophobic parts - the parts that
don't like water - can escape water contact. |
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Sooner or later, the surface will be fully occupied by
soap molecules. Unlucky molecules will have to find another
way to escape water contact. Air bubbles, created under the
tap, are perfect for that.
Air bubbles dive into water following the momentum of the
flow from the tap. |
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They get surrounded by soap molecules and, because air
is lighter than water, the bubbles want to get back up to
the surface. |
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Then, on the way up the air bubble with soap surrounding
it meets the water surface, which is filled with other soap
molecules. |
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And this is how a soap bubble is created. It's a sphere
of air,surrounded by a layer of water that is trapped between
soap molecules.
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This would be nice but soap bubbles can't fly. The
weight of the bubble, including its air, water and soap, is heavier
than the weight of the same volume of air (even without the duck).
Hence, following Archimedes' principle, bubbles can't fly.
Find out more about floating and sinking in floating
duck chapter.
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