Surface Tension
Third grade Chemistry lesson
Liaison: Sadhna Vora
Date: 3/23/99
Group Members: Kevin Gold and Eva Holtz
School: Tobin
Teacher: Mary Hill
Materials:
A bar of soap
A cutting implement
Construction paper
A piece of string
A cup
A dish or two
Pepper
A toothpick
Procedure:
I. Introduce concept of surface tension with overfull cup, asking why it doesn't
spill over. Ask why drops of water are round instead of square. Answer: surface
tension.
II. Can surface tension be broken? Fill dish with water and sprinkle pepper on top.
Touch surface w/ bar of soap - the pepper scatters. Repeat with loop of string:
it forms a circle. Explain why: the surface tension outside pulls the string out equally
in all directions. Relate this to why raindrops are round.
III. Interesting -- but can we make a vehicle out of it? Put a chip of soap on the rear
end of a piece of paper having a vague resemblance to a boat, and make it so. Warp speed
ahead!
IV. Play a game with some kids as water molecules, others as soap molecules. Boundary
is the carpet circle area. Water molecule kids have to touch (lightly) two other
water molecules, unless a soap molecule comes between the two -- then that person
touches instead with that hand a farther away person that's close enough to touch. The
soap molecules get to wander around and break up water molecule links. If a water molecule
has no farther out person to touch, that hand's free. If two hands are free, that water
molecule is a winner! Switch off teams.
V. A worksheet on surface tension, asking questions like, "Why can you fill a glass
over the top without spilling?" and "Why are water drops always round?" and
"How does a water spider that's heavier than water walk on water?"
Evaluation:
I. Intr
Comments:
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