Flying Circus of Physics

Flying Circus of Physics

Newsletter May - July 2013

One of my favorite toys as a child were tops. Long before I knew any physics, I knew there was something magically wrong with a top. From my efforts in learning how to walk, I built up an intuitive sense of balance. From my activities on the playground, I knew that if I didn’t keep my balance, I fell over. From my lessons in judo, I learned how to ruin my opponent’s balance to cause a fall. But a spinning top is fundamentally different, as if all the intuitive and physical laws of balance just don’t apply to something so elegant and beautiful.  Even when a top leans over appreciably, gravity seemingly ignores it.

      Physicists long ago worked out the special dynamics of spinning objects, discovering that the secret lies in a nonintuitive quantity called angular momentum. Well, it is certainly nonintuitive until you struggle through a classical mechanics class. The angular momentum is associated with the spin rate and the distribution of mass around the spin axis. One peculiar result is that when the gravitational force pulls down on a leaning top, the resulting motion is perpendicular to the pull. The top will then precess; its spin axis can trace out a cone and even bob up and down while tracing it out.

     Here is a link the wonderful film made by Charles and Ray Eames about tops, with a score by Elmer Bernstein. Note not just the charm of the tops but also the wide range of personalities: some stand upright like a soldier at attention, some precess with its contact point on the table fixed in place, some precess with its contact point tracing out an ellipse, and some even invert.

http://www.youtube.com/watch?v=UJ-VFMymEiE

In this second video we are treated to the collection of tops by Ian Russell, including the rattleback, the toy that will reverse its spin if spun in the “wrong” direction.

http://www.youtube.com/watch?v=LDXAhwhsZ9k

I’ll give you one more top video, showing a street performer with as large a top as anyone can manage:

http://www.youtube.com/watch?v=Db4lH3BZE0Q 

The May stories at the main FCP site include examples of very large and energetic bathtub-type vortexes that form over drains. One draining vortex was responsible for emptying a lake into an underlying salt mine, consuming several barges in the process. Another story deals with one of my fascinations (or perhaps one of my shear fears): very deep holes, ones in which I would fall almost forever. In the videos stones are dropped into the holes, thus allowing us to approximate the depth by the time of fall. In one hole, we hear a stone land 11 seconds after it was released, giving a depth of about 450 meters. But in another hole, we hear the stone land 35 seconds after it was released, giving a depth of about 3.2 kilometers. That really kicked up my nightmares.

More videos and photos have been added to the FCP Facebook site (you do not need to be a member):

http://www.facebook.com/pages/Flying-Circus-of-Physics/339329532602?ref=ts

Cheers,

Jearl Walker