When pouring a glass of water, one might observe that it flows much quicker than pouring syrup on a pancake. The measure of this resistance to flow is called viscosity. All liquids flow, but depending on the size of the molecules in that liquid, they will flow at a different rate. When the molecules are close together and exert a large amount of friction on each other, the liquid will flow more slowly. The less friction they exert on each other, the faster the liquid will flow. Elementary students can experiment with viscosity through several hands-on experiments.
Viscosity and Temperature
Students can complete an experiment in which they determine if temperature affects viscosity. Begin by allowing students to observe vegetable oil and water being poured. Discuss with students which one flows more quickly and that vegetable oil has a higher viscosity. Give students three glasses filled with water and three coins. One glass of water should be room temperature, one ice cold but not frozen and one warm but not boiling. Students should drop the coin into each glass one at a time and using a stopwatch measure the amount of time it takes the coin to reach the bottom. Students should observe that as temperature increases, viscosity decreases.
Creating a Viscometer
A viscometer is a tool used to measure viscosity, and in this experiment your students can create their own and calculate the viscosity index of several fluids. Viscosity index refers to the viscosity of a fluid compared to the viscosity of water. To create the viscometer: begin by cutting off the bottom of a clear plastic liquid detergent bottle. While holding the bottle upside down, measure one inch below the cut off bottom and write "Start". Measure four inches below that line and write "Stop". Next, mould clay around the top of a glass jar and place the detergent bottle upside down into the glass jar. Now begin testing using cold water, by pouring the water into the detergent bottle and pulling the top open before placing back on the glass jar. Using a stopwatch, begin timing when the water level is at the start line, and stop when it reaches the stop line. Record the time in a data chart and repeat this procedure with various liquids such as corn syrup, honey, rubbing alcohol and shampoo.
When lava flows from a volcano it does so at different rates, depending on the volcano's height. Students can create volcanoes of various heights and observe how this affects the viscosity of the lava. Have students create three volcanoes by moulding clay around paper cups. One volcano should have very steep sides, the other moderately steep sides, and the last very gently sloping sides. Mix together nine tablespoons of vinegar and a teaspoon of dishwashing liquid and put a tablespoon of baking soda in each cup. Make the volcanoes erupt by slowly pouring the vinegar mixture into each cup. Have students observe the rate at which the liquid flows from the volcano and how far the liquid travels.
Students can create a mixture that is similar to quicksand and observe its unique viscosity. Mix together about four ounces of cornstarch and 1/2 of water and stir or mix with your hands. Add more cornstarch if necessary, until the mixture resembles the consistency of honey. Allow students to experiment with this mixture by placing their hands or another object into it. Students will observe that the faster they move their hands the thicker the liquid becomes and that when an object is dropped into it, it is difficult to remove. Students can try rolling the mixture into a ball and pouring it onto a baking tray. This mixture is an example of a non-Newtonian mixture because its viscosity changes when force or stress is applied to it.