Activity 8.
Make a paper boat. Put it in water and push it with one narrow end pointing forward [Fig. (a)].
Did it go into the water easily? Now hold the boat sideways and push it into the water from the broad side [Fig. (b)]. Are you able to make the boat move in water when you push it from this side?
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Answers
Materials:
A flat tray about one inch thick (a cookie sheet or a cake pan works), water, an index card, liquid or bar soap, scissors.
Procedure:
1. Fill the tray up with water (not too full, it is hard to move it without spilling it if full… in fact, do this near a sink!)
2. Cut an index card into the shape seen below
3. Place the paper “boat” in the water at one end
4. Put a small drop of liquid soap at the small triangle cut of the boat
5. Watch the action!
6. Alternative: you can touch a corner of the bar soap into the small end of the triangle as well.
Explanation:
You should have seen the paper boat scoot across the surface of the water, much like it was afraid of what the soap was doing to the surface. It’s true. The paper boat is being held on the surface of the water, and that surface is weakening. Here’s what I mean:
Water has a strong surface to it, called “surface tension.” The reason behind this is due to some complicated chemical explanations of the water molecule. We’ll keep it simpler and just say that water sticks to itself pretty well, especially at the surface. Some things we see because of this are leaves floating on the surface of the water, bugs skipping across the top of it, even the fact that water forms “drops” on things.
Soap weakens this surface tension. So things that were floating on the surface have a harder time being held up. In this instance, the paper boat scoots away from the weaker part of the water to the stronger, more held together part.
Experiment further:
Will the shape of the boat affect things? Will it make it go faster, slower, sideways…? What about the material of the boat? You can have races with different boats, types of soaps…don’t just do one thing. Be a scientist and try out different things!