Water
 Water molecules like each other very much
 Water molecules like to be as close to one another as they can
 Water molecules “attract” to other water molecules
 Water molecules are not attracted to particles that they do not like
 Water molecules do not like things like dirt and oil
Soap
 We use soap to clean things
 Soap and water are different from one another
 When soap and water are mixed, the soap stays on top of the water
 Soap bubbles are attracted to other soap bubbles
 Soap bubbles like things like dirt and oil
 Soap bubbles are attracted to dirt and oil
Paper Clips
 Paper clips are made of metal
 Metal does not usually float on water
 A paper clip can be made to float on water using surface tension
Surface Tension
 Surface tension is the force that pulls water molecules on top of the
water close together
 Water’s surface tension can be reduced by soap
Activities
I. Overfill a glass
a. Pour water into a glass.
b. As it nears that top, pour the water more slowly.
c. Once the water level has reached the top of the glass, pour in a little more
water.
d. A bubble of water will form above the rim of the glass.
e. The bubble forms because of surface tension: the water molecules at the top
f.
g. are all attracted to one another and pull tightly to form the bubble.
II. Float a paper clip
a. A paper clip is made of metal that will not float on top of water by itself.
b. Unbend a paper clip and lay a second paper clip across the unbent paper
clip.
c. Use the unbent paper clip to lower the other paper clip on top of water that is
in a bowl.
d. If the paper clip is held at the top of the water in this way for a short time, the
unbent paper clip can be carefully removed, and the paper clip will float on
top of the water.
e. It floats because the surface tension of the water was broken by the bent
paper clip and was allowed to re-form around the other paper clip. This can
be seen if one carefully observes the water clinging to the bends of the paper
clip.
III. Push pepper to the edges
a. Pour water into a bowl.
b. Sprinkle a little pepper all over the top of the water.
c. Put a small dot of dish sop onto your finger tip and rub it in.
d. Put your finger into the center of the bowl of water.
e. The pepper will all move out to the edges of the bowl.
f. This happens because the soap weakens the water’s surface tension in the
center. The pepper will then move to the outer edges of the water because
the surface tension is stronger there where there was no soap initially.
IV. Race paper clip boats
a. Make a paper clip float in the center of a bowl of water as done in the second
activity.
b. Put a small dot of soap onto a toothpick and rub it in.
c. Put the toothpick into the water behind the paper clip to push it.
d. This works because the soap weakens the water’s surface tension at the
point the soap touches it and the paper clip is pulled to an area where the
surface tension is still high.