Bubbles on the surface of a liquid are held
together by surface tension.
Let's look at
water... Because water molecules are polar (each
end has a different electrical charge), they are
attracted to one another. This attraction of
water molecules to each other is the source of
surface tension. Under the surface, a water
molecule share its attraction with molecules on
all sides of it. Water molecules on the surface
do not have other molecules on all sides of them,
so they share extra strong attractions with their
neighbors. This occurs whenever water is in
contact with air and is called surface tension.
Surface tension is what makes bubbles in water
round. The surface tension between water
molecules pulls them into the tightest package
possible, a sphere. As the surface tension pulls
the molecules together, the air inside pushes them
apart. Eventually, the pulling and pushing
reaches equilibrium, and the bubble stays the same
An exception to the rule is when bubbles
rise through water. The pressure on a bubble at
the bottom of a container of water is much greater
(the weight of the water pushes down on the
bubble) than the pressure on the bubble at the
surface. Therefore, bubbles at the bottom are
smaller than bubbles at the top. So, as a bubble
rises through a column of water, it will become
larger as it rises. You can probably think of
ways to experiment with this at home!
in a glass container will adhere to the sides of
the glass because of the adhesive force between
water and glass.
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