Friday, April 26, 2013

A Science Fair Project Using Stuff You Already Have in the Kitchen!

Turns out viscosity is actually kind of interesting.  Here, Chop is timing how long it takes for a teaspoon of maple syrup to drip.  She had a surprise when she learned how long it took to freeze!
This was actually an experiment that "Chop" thought up for her 6th grade science fair, but it's safe and easy to do with smaller children.  My husband "Gandalf," who helped her, was adamant that we use only edible substances (a safety thing).

Chop wanted to know if "thicker" liquids freeze faster than thin.  She thought they ought to, since something like honey or syrup seems like it's already halfway to solid.

The scientific term for the thickness of a fluid is "viscosity."  A more viscous liquid, like maple syrup, is stickier and flows more slowly.  Chop picked out various liquids with very different viscosities:  water (the least viscous), canola oil and olive oil (slightly more viscous), and corn syrup, honey, and maple syrup (very viscous). Gandalf hates to waste food, especially expensive food (e.g., olive oil), but the experiment uses only a little bit of each liquid.

The first job was to measure viscosity.  Since viscosity is just a measure of how slowly things flow, first Chop tried to measure it by filling up a tablespoon with each liquid, tilting the tablespoon sideways, and timing how long the liquid takes to flow out.  This worked well for the more viscous liquids, but things like olive oil and water flowed too fast, so she abandoned this idea.  We thought, "Great!  This is what science is all about!"

After some brainstorming, Gandalf suggested a clever solution.  Raising 6 kids, we have lots of medicine syringes lying around the kitchen, courtesy of ear infections and strep throats of long ago.  So he took an open syringe (i.e., without the plunger), filled it up to the top with a liquid, and put his thumb over the top to stop it from flowing out.  Then he released his thumb and timed how long it took the liquid to flow out.  (Can you guess which of our liquids was the most viscous?  Answer at the end).

This was taking forever so we got lazy.....
Then we poured an equal amount of each liquid into a small plastic container, Chop carefully labeled them, and we put them in the freezer.  She checked every ten minutes to see which liquids froze first.  The interval lengthened as we realized it was going to take FOREVER..........

These little plastics cups were leftovers from an art camp.
It was fun just to see how each liquid changed as it froze!  For instance, the olive oil congealed into something with the consistency of butter.  But the more viscous things took longer to freeze, and the least viscous liquids froze first!  We thought, "Way cool!  This is the opposite of what we thought would happen!"



A quick trip to the internet cleared up this mystery.  For something to freeze, the molecules have to arrange themselves into an orderly lattice shape.  But when a liquid is more viscous, it's harder for the molecules to move around, and so it takes them longer to find the right "place" to form a solid.

OK, now which household liquid was the most viscous?  Honey, by far.


  1. Very interesting! I guess that's why auto antifreeze is so thick and syrupy?

    1. Here's a few sentences I found on that:'t_antifreeze_freeze