You have probably noticed water droplets often appear to seek out other water droplets becoming a bigger and bigger blob, like rain on a window. Or maybe you have noticed little bugs standing on water. How do they do that? It all has to do with the property of water known as surface tension. In today’s experiment we are going to explore just what a powerful force that can be.
Surface tension can explain why small insects can walk on water and why water droplets tend to form a spherical shape. It all has to do with the way water molecules like to stick to other water molecules.
A water molecule is made up of one oxygen atom and two hydrogen atoms. These atoms connect by sharing electrons. Due to the forces that connect the hydrogen atoms to the oxygen atoms, a water molecule tends to have one side that is little more positive and another side that is a little more negative. This causes the negative side of one molecule to attract to the positive side of another molecule. Thus, water molecules push and pull themselves into a certain arrangement. This equilibrium is where all the positives and negatives balance each other. In the middle of the water those forces are pulling in all equal directions. But on the surface, something a little different happens. On the edge of the water, along the surface, water tends to arrange so that the molecules on the surface get pulled towards the rest of the water molecules. This pulling creates a thin layer of water molecules that link together creating the surface tension we will see in this experiment.
There are lots of ways to extend this experiment and better understand surface tension. Do you think all liquids have the same surface tension? What if you tried milk, orange juice, or vegetable oil? Would you get the same results? What if you mixed things into your water, will that change the surface tension of the water? Try adding soap or salt to your water and see if that affects your results.
Remember you only want to change one variable at a time so you can better understand what is causing your results to change.
This experiment was selected for Science at Home because it teaches NGSS Disciplinary Core Ideas, which have broad importance within or across multiple science or engineering disciplines.
Learn more about how this experiment is based in NGSS Disciplinary Core Ideas.