Today’s lesson was all about viscosity. Viscosity is fluid friction, which we can describe as the interactions between molecules of a fluid that affect the rate at which that fluid is able to flow. Viscosity is not related to density or stickiness, but the charges between molecules and how strongly they are attracted to each other, which is also affected by temperature! First we talked about examples of fluids and learned that both liquids AND gases are able to flow. We demonstrated this by generating carbon dioxide gas in a beaker and pouring it over a lit candle to “blow” it out! Then we compared different fluids such as water and honey in terms of their viscosity.
For our activity, we had a viscosity race between six common fluids including some you might find in the bathroom, kitchen cupboard, or even in your family’s car! Working in groups, students set up a test of the viscosities of the different liquids. First they made hypotheses about which fluids were more viscous and less viscous based on their appearance in small bottles. Using a cookie sheet, they placed drops of their liquids on the sheet, raised one end for a specific amount of time, and then measured the distance each drop traveled. The students then compared their findings to their hypotheses. The students should all have a much clearer understanding of the expression “slower than molasses in January” now! Some groups got slightly different results which gave us an opportunity to discuss flaws in our experimental design that could have been to blame.
This is an activity that is easy to try at home, with as many different fluids as you can find (detergent, lotion, shampoo, syrups, pudding, yogurt, etc). You can also look at the effect of temperature on viscosity (how warm does Vaseline need to be before it will flow?)…. Happy experimenting!