It's that time of year where school is starting and that means teachers have to go over the safety rules in the science classroom. Teachers who teach chemistry must have all of their students wear safety goggles during lab activities. Being a teacher, whose middle school students don't really want to wear them, I have a simple demo for students to understand the need to wear them.
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Students often have misconceptions about certain science concepts. They occur naturally and they do not happen because a student is not intelligent. The human brain tries to fit information in an easy to digest construct, even though it is not accurate. Misconceptions are very difficult to break. The best way for students to break their misconception is to articulate their understanding and then try confront a demo or new piece of information that contradicts that misconception.
In the video some teachers are asked the question, "What causes the phases of the moon?" They then are asked to demonstrate their thinking and to explain how it works. An explanation and demonstration of how the phases of the moon actually happen takes place in the last third of the video.
Here on Earth, friction is an unbalanced force that will cause moving objects to negatively accelerate. A top is a classically fun toy that spins for a period of time. Tops stop spinning because of friction forces between the top and the surface it is spinning on (as well as some friction with the air). Using a top that doesn't stop (available at Educational Innovations) and a normal top, this demo offers a discrepant event for students to experience. They know that all tops stop, but don't neccessarily know why, and they will be especially preplexed when they see a top that does not stop spinning. Watch the video to see it in action and to see why it doesn't stop spinning.
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.