manual

26
As the coins are added, the water level rises above the
rim of the cup but it does not spill over because water
molecules are attracted to one another.
Look carefully at the edge of the curved surface of the water. The liquid
has a “skin” that has formed because of the surface tension of the water
particles (molecules). This “sticky” surface tension happens because the
hydrogen atoms in one H
2
O (water) molecule are attracted to the oxygen
atom in the neighboring H
2
O molecule.
Surface tension allows insects to land on the surface of the water and even
lay their eggs on it.
Try this:
Use surface tension to float a paper clip on the
surface of the water. (It may help to cut a piece of
paper towel slightly larger than the paper clip.
Lay the towel on the surface, float the paper clip
on the towel, and then carefully slide the towel
out from underneath.) Voilá! The paper clip
is floating on the water’s “skin”!
The surface tension (water’s “skin”)
allows the water’s surface to “stretch”
upward before breaking.