This is one of my favorite demos to show how mass determines the inertia of an object. If you are going to do this demo in class, make sure you use fishing line that can handle the highest tension possible (great demo for tension as well) that you can buy at a local sporting goods store. I used goop adhesive to attach a paper clip to the golf ball, so that I could tie the fishing line to the golf ball. I tied both objects to the metal beams of the drop down ceiling in my classroom. Watch the video to see how the demo works.
Students have a major misconception that mass determines whether an object floats or sinks. This is an activity that forces students to deal with that misconception and hopefully break it. The following materials are needed:
Have the students read the statement, "Objects that are high in mass, sink in water." Have the students show in some way if they agree with the statement, disagree with the statement, or are somewhat in between. Have them explain why they think that way and give examples. Then present the students with the list of all of the items to be placed into the tank, arranged according to their masses. Do not show the objects to the students. Have them write a hypothesis for each item (on whether they will sink or float) based only the property of mass. Then drop each item one by one, in order of their masses, into the water. Have students record the results. The students will realize that mass has nothing to do with whether an object sinks or floats. Then show the students the objects' densities. Hopefully they see the pattern of those objects with densities less than one float, and those with densities greater than one sink. It is not important to explain what density is at that point, but just that it is a property of matter that is vital in determining if an object floats or sinks.
For this demonstration I use my own special formula for extra strong soap bubbles. I use one part Dawn soap, one part glycerin, and two parts water. I dip the bottom end of the funnel into the soap bubble mixture and blow through the wide top to create large bubbles. The rest of the demo just needs an empty fish tank and some dry ice. This is one of my favorite demos to teach the concepts of the density and buoyancy of different gasses.
Demonstrating the density of diet sodas versus regular sodas is a classic, but something unexpected happened when I placed a can of Dr. Pepper and A & W root beer in a tank of water. They didn't follow the usual pattern of results. Watch the video and please respond if you can provide an explanation for the results.
Can saltwater, water, alcohol, and shampoo be stacked? This is a very simple student inquiry activty (and one of my students' favorites) that can be done in class (download handout).
Tuesday, May 29, 2012 at 6:19AM 