Awkward Orbits

What It Is

A box or other object with 3 different lengths. (Like a cereal box.)


What You Do
These boxes have three different axes; try spinning them on each. Notice how they spin. After a while, you might notice that two of the axes allow for relatively stable spinning, but the spin of one axis is never stable.

What You Learn

Inertia and polhode motion are the main concepts at work here. Depending upon which axis you spin these blocks, they will (or won't) spin smoothly. The force required to get the spin going is in play, and will affect the stability of certain axes. (Namely: the two which require either the least or most amount of force.) The axis which requires the median amount of force will never have a stable spin.

How You Make It

We have a few, but really you only need one. Something the shape of a box is what you need -- that is, a rectangular prism which has three different lengths. That said, most cereal boxes, if empty, are probably too big for this to work very well. The boxes that we use are only about 1" x 2" x 6", approximately. A mac and cheese or easy rice box might prove more useful.

Display Sign Text

What to do: The foam blocks have three axes, like in the picture. Toss one of the foam blocks and try to get it to spin twice in the air without tumbling around one axis. Now turn it, and toss it on a different axis. Will it spin smoothly on all three? Try tossing the block back and fourth with a friend, trying to make it spin on the axis without tumbling.
What is Happening: All objects have something called inertia: the ability and desire to resist change. This means that if the block is moving, it wants to stay moving. If you were to put a stick through the block at each axis it will take more or less force to make it spin. Axis #1 would take the least, axis #3 would take the most. Because of this, when you spin the block in the air, axis #1 and axis #3 are stable. It will spin easily and you can toss it to a friend that way. However, the block will never spin smoothly about axis #2 when tossed in the air - this is called polhode motion.

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