Kids, do you know what lubricants are? They help reduce friction, or wear and tear, between moving parts. They can be solids such as graphite, soap, or talcum or they can be liquids like oils and greases. An important feature of a liquid lubricant is its thickness or ability to flow. This quality is called viscosity. Look up viscosity in the dictionary and it says, among other things: "the property of being glutinous or sticky". Well this certainly sounds like it could be a fun property to experiment with. It is the job of chemists to create and analyze lubricants. But you can easily tell which ones are more or less viscous than others by doing this simple experiment.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
You will need 3 tall, narrow, clear jars with lids (olive jars or baby food juice jars), vegetable oil, clear shampoo, clear dish detergent, and 3 chocolate chips. Nearly fill one jar with the oil, one with the shampoo, and the last one with the detergent. Make sure all the levels are the same. Gently place a chocolate chip in one of the liquids. Time how long it takes to reach the bottom with a stopwatch. Make a chart and record the time. Do the same thing with the other two chips and liquids. Or, you can make a race out of this with two friends. Place the chips in the liquids at the same time and see whose goes fastest and slowest.
Determine which liquids have the shortest time, the next shortest time, and the longest time. For the jar with the shortest time for the chip to reach the bottom, is the liquid in that jar more viscous or less viscous than the other liqudis? Hint: the longest time = the most viscous liquid.
You can make these jars reusable by sealing the tops on with Kraft glue. If you do this, seal a different colored marble into each jar rather than a chocolate chip.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
February 1999
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Reference: "WonderScience" March 1990 issue and M. Ebeling (primary level teacher, Naperville district 203).
