Newton's Third Law Demonstration
Date: Winter 2011-2012
I am trying to do a different type of activity with my students to teach Newton's Third Law. What I would like to do is employ a childhood activity that I used to do. It consists of a large button on a string, I think they called this a button on a string spinner. What I need to be sure of is that this activity really does represent Newton's Third. Since the string is pulled in opposite directions as if it were an elastic/rubber band, I am thinking it probably does. However, I want to make sure.
Any time there is a force, Newton's third law is in play. But the device you describe involves two equal and opposite forces applied the same object: their Newton's third law pairs are the forces that the device applies to each of your two hands.
My favorite Newton's third law demonstration is to stand on a skateboard and pull on a fixed rope. I move in exactly the opposite direction that I pull, so the rope MUST be applying a force on me in the direction opposite the force I apply to it!
Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
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Update: June 2012