Surface Tension

Lisa C. Ingram Frederick Douglass Middle Academy
543 N. Waller
Chicago IL 60644


To understand the concept "Surface Tension", through several experiments.
Designed for students grades 5 through 8.

Materials Needed:

Overhead projector (teacher demonstration)
2 glasses of equal size and depth
a bucket
pennies 60 per group or person
bowls 2 per group or person
a box of toothpicks
liquid soap or detergent
a box of cube sugar
clear cups 1 per group or person
bubble solution
bubble wands or other bubble instruments


Students will be asked to brainstorm what surface and tension mean. Also,
discuss where they have heard the words before. All comments will be written on
the black board. After all demonstrations students will comeback to these
comments and form a definition(s).

Experiment 1: Teacher will fill two glasses underwater. Then take them out of
the water, holding them rim-to-rim so no water escapes. Stand the glasses on a
flat surface so that one rests upside down on top of the other. Teacher will
slide one penny between the two rims. When the coin is in place, water molecules
will pull together between the rims and stop the water overflowing.

Question: Why did the water stop dripping, even though there is still an

Answer: The molecules are pulling and stretching to form a skin to the water.
Thus no water can get out, unless the surface tension is broken.

Experiment 2: Teacher will use the overhead projector to demonstrate. Arrange
toothpicks in a circle in a bowl of water. Place a cube of sugar in the center
of the circle (place bowl on top of overhead projector). Take another bowl,
arrange the toothpicks in a circle again. This time place aa piece of soap or
liquid detergent in the center (place the bowl on top of projector). Students
should observe and verbally respond, the toothpicks went toward the sugar and
they went away from the detergent.

Question: Why did the sugar draw the toothpicks and why did the detergent repel
the toothpicks?

Answer: The sugar sucks up water, creating a current that carries the
toothpicks with it toward the center. The soap, on the other hand, gives off an
oily film that spreads outward. It weakens the surface tension, and the film
carries the toothpicks away with it.

Experiment 3: A clear cup with a drop of food coloring, should be placed on top
a white piece of paper. Near by should be a bag of at least 60 pennies.
(Teacher should set these items up, as stations, in the designated area before
children begin) Explanation: Tell the students that they are going to fill
their cups up to the brim with water. They will then have someone slide pennies
into the color cup of water, until the color water drips on the paper. Tell
students not to throw the pennies, they want a drip not a splash. One student
in the group should be designated to count the pennies going into the water.
They are to this until there is a drip on the paper.

Question: Why does it take so long for the water to drip?

Answer: Surface tension builds around the cup, until it is broken with a penny.

Performance Assessment:

Students will be asked to explain surface tension verbally. They will also be
instructed to write one or two sentences defining surface tension.

Return to Physics Index