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Inverting Pop Tops

  • Inverting Pop Tops - Natural Wood (bag of 5)
    Item #: TOP-300
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  • Inverting Pop Tops - Natural Wood (bag of 20)
    Item #: TOP-305
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  • Inverting Pop Tops - Red (bag of 5)
    Item #: TOP-330
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  • Inverting Pop Tops - Red (bag of 20)
    Item #: TOP-335
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Description

When these small wooden tops are spun, they start precessing until the heavier hemispherical end is lifted, seemingly against gravity. The Nobel Museum in Stockholm reports that Neils Bohr was captivated by this top when first observed over 50 years ago. These newly designed tops, with a hollowed out sphere, are like the original and work extremely well! The natural wood ones can be decorated by students. 3.8 cm (1.5") tall, 3.2 cm (1.25") dia.

Video


Lesson Idea

Download the pdf of this lesson!

Instructions:

With the hemispherical bottom downward, spin the stem of this top and release it onto a flat surface. The top will spin for a few moments and then mysteriously invert so that it continues spinning on its stem with the heavier hemispherical bottom lifted. Jearl Walker in Roundabout, The Physics of Rotation in the Everyday World (W. H. Freeman and Company) describes this top as 'the most fascinating top I have ever encountered.'

Explanation:

When the top is spun, the frictional force on the hemispherical bottom causes the top to start precessing. This sliding frictional force creates a torque on the spinning mass, which causes the top to invert. A hard-boiled egg can also be used to show this phenomenon. When the egg is spun on its side, it will rise up to spin on its end.

Jearl Walker writes in the October 1979 issue of Scientific American:

The motion appears to violate the law of conservation of energy because the top seems to raise its center of mass (which is in the spherical section) without outside help.

The top has long fascinated observers, including several distinguished physicists and mathematicians. In a recent paper, Richard J. Cohen of the Massachusetts Institute of Technology describes how William Thomson (the eminent physicist better known as Lord Kelvin) spent his time spinning smooth stones on the beach instead of preparing for his mathematical examination at the University of Cambridge. Later Niels Bohr, who developed the first modern model of the hydrogen atom, became similarly entranced with the mechanics of the Tippe Top.

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Reviews

5 reviews
Tops
Review star icon Review star icon Review star icon Review star icon Review star icon Dec 19, 2015
Not all of the tops work. Some spin and flip up with ease and others regardless of spinning attempts did not. The ones that work were great.
Helene

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Challenging
Review star icon Review star icon Review star icon Review star icon Review star icon Apr 22, 2014
You need a lot of space to twirl these enough to spin and flip. They are a good challenge for everyone so a lot of fun.
Marilyn Gorman

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teacher
Review star icon Review star icon Review star icon Review star icon Review star icon Dec 27, 2012
They don't invert as easily as I was expecting and they stay inverted for a very short time. A disappointment.
Warren

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Stimulating Teaching Tool
Review star icon Review star icon Review star icon Review star icon Review star icon May 23, 2012
Great tool for teaching physics concepts to all ages. Stimulating and lots of fun to use!
B Lewicki

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Magic or Science?
Review star icon Review star icon Review star icon Review star icon Review star icon May 22, 2012
These inverting pop tops were a class favorite. I showed how to spin one, then everyone in class started spinning their own.It was a good thing I got enough for each student to decorate their own so they could find theirs as some tops "spun off." We were most successful spinning them on the floor. When some of the kids had trouble getting theirs to work, other students jumped in offering to show them how to be successful. It was a fun activity and students were trying to figure out why they flipped (students initially determined they must be magic)! After my class they showed students from other classes. How do I know? Other students came to my room wanting to know if I had any more!
Gail Schwoebel

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