Take the weekend off and smell the physics

Yeah, like you’re too grown-up and sophisticated [/MockingTone] to find this simple demo fun and fascinating.
Show it to your grand-kids and say, “See? We old folks know about dangerous stuff.”

The pendulum effect determines the period/frequency of each ball
(a function of length and gravity, not weight/mass or release distance),
but the nerdy fun here is how it illustrates resonance in periodic functions.

You should see the motion evolve through several noticeable stages:
groups of 1-5?-4-3-2-3-4-5?-1
4 isn’t an integer multiple in 15, so you get 4/4/4/3 balls in that phase.
2 isn’t either, so you get 7/8 balls.
I figure there’s gotta be a 5 phase (3/3/3/3/3) in there, too, and more; but I can’t see ‘em.
The DNA-like double-helix is the most interesting to me — pseudo-biological order from apparent chaos (totally unrelated, but cool).
The math is left to the student — been wayyy too long ago for me (at least I didn’t have to look-up the definition of pi).

1) What happens to the pattern if you add or subtract a ball?
2) What happens to the pattern if string lengths aren’t a linear series?
(etc. We can do this all term long)
Extra Credit:
Identify each ball’s number without looking at the numeral on it.


  1. Claire: rebellious pink pig with car keys - and a *cause*
    Posted June 9, 2019 at 6:54 am |

    I’ll show up for that — all term.

  2. dick, not quite dead white guy
    Posted June 9, 2019 at 11:00 am |

    Neat! Wish I could remember how to deal with the numbers of that, but it’s been way too long ago.
    Describing the patterns numerically would be a great exercise for STEM students.

  3. Veeshir
    Posted June 9, 2019 at 6:08 pm |

    Not as cool but when I was a kid I went to a museum a couple times, I can’t remember which one but it was either in Albany, NY or NYC.
    They had a dome with a weighted rope, pendulum, hanging down with a ring of cones around it in the rotunda.
    In the morning they would start it.
    As the day progressed it would sweep around the circle knocking down the cones. 6 hours later it was 1/4 of the way around the circle.
    It didn’t move, the room did the object in motion tended to stay in that motion.
    Smart guy that Newton.

  4. DougM (speak three names)
    Posted June 9, 2019 at 6:21 pm |

    ^ Yeah, I liked that one as a kid, but I thought it proved the Earth was flat or something.
    Dunno, I paid more attention to the cutie with the saddle shoes and braids.

  5. dick, not quite dead white guy
    Posted June 9, 2019 at 9:34 pm |

    ^^ Foucault pendulum proved the earth rotates. The table turns with the earth under the pendulum while the pendulum’s motion remains its same fixed spatial plane.

  6. drew458
    Posted June 10, 2019 at 11:14 am |

    Thanks Dick, you beat me to it. I remember seeing one of those myself. Big tall thing, and a little spike under the ball would knock over dominoes as the earth went around. It would swing for hours.

  7. Veeshir
    Posted June 10, 2019 at 10:33 pm |

    Foucalt! I knew that but totally forgot.
    And he’s my favorite sciencey/math guy whose name sounds like a cuss too.

  8. rickn8or
    Posted June 11, 2019 at 9:38 am |

    I bleeve the pendulum you’re talking about is (or was) at the Smithsonian in DC. (At least the one I saw was.)

  9. DougM (speak three names)
    Posted June 11, 2019 at 12:36 pm |

    Here’s a nerdy vid that shows a pendulum-day in only a few minutes.
    Y’might also learn why clockwise is clockwise. I did.

    (Everybody knew a pendulum-day’s length varies by latitude, right?)