Thursday, January 19, 2012

Bouyancy and Forces Science Demonstration: Floating Corn Kernels with Kitchen Basics (Optional Experiment Included in the End)

You know I am a sucker for introducing kids to science. I have added different levels of discussion for this demonstration based on age. Using easily found items (I may be the only one who still makes popcorn in the microwave with a brown paper lunch bag, so maybe not all of them are right in your cupboard), show a number of different science concepts.

Materials (when you look at the videos, you can see that I had no idea how much I was using of anything):
  • A clear, tall container—I used a 1 quart Mason jar
  • 3 cups of water
  • ¼ to 1/3 cup of baking soda
  • 1/8 to ¼ cup of unpopped popcorn kernels
  • ½ to 1 cup of white vinegar
  1. Mix baking soda and vinegar in the clear container
  2. Add corn kernels
  3. Pour in vinegar (Over or near a sink! It may foam over the top.)—it may need a little stir
If you do not have a 1 quart container, try halving the amount of water, baking soda, and vinegar.

Middle schoolers through toddlers can learn something from this demonstration. My guy was thrilled to see something change. I showed him the bubbles on the kernels and, that when the kernels reached the surface, those bubbles disappeared and the kernel sank.

Older children, elementary-aged, might look at how many bubbles it takes to make the kernels rise. Bubbles float and, when there are enough bubbles on a kernel, that force is more than the force of gravity pulling the kernel to the bottom. They will see quickly that the amount of bubbles on the surface will determine whether the kernel will rise or fall. Try to figure out how many bubble are needed before it rises.

With middle schoolers, start with the same concepts above. They may already know that the bubbles are pushed up by an upward force called bouyancy. The bubbles are bouyant because they are not as dense as water. Each bubble adds its upward bouyant force to the other bubbles on the kernel (a cool property called force superposition).  The kernels rise when the bouyant force is larger than gravity.

More in-depth: Ask your child where the bubbles are coming from. Turn this activity into a science experiment by putting kernels in plain water, water with baking soda, and water with vinegar. Are lots of bubbles forming on the kernels in any of those? What about seltzer water? A chemical reaction occurs when baking soda and vinegar are put together. They create carbon dioxide. Carbon dioxide gas dissolves in water. Seltzer water also has carbon dioxide dissolved in it.

For those who just can't get enough, ask why the bubbles appear on the kernel (and wall of the container) at all. (Bubbles like to form on tiny, sharper places, nucleation sites.) They can try to estimate how many bubbles it takes to get the kernel to move up.  
Kim McNeill is the editor and publisher of Macaroni Kid for Southbury, Oxford, Woodbury, and Middlbury CT, blogger at Hearst CT Media Group, Kim's Play Place, the Waterbury CT Family Entertainment Examiner and freelance writer for CBS Local in Connecticut.

1 comment:

Michelle Bridger said...

Wonderful! I'll give it a try thanks!