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Science Idle

The Physics of Jump Rope 29

Posted by samzenpus
from the because-he-can dept.
sciencehabit writes "Last year, Jeffrey Aristoff and Howard Stone, mechanical engineers at Princeton University, were at the gym waiting for a pickup game of basketball. To warm up, Stone started jumping rope. As the rope whizzed over the head of his colleague, Aristoff wondered, 'Is it known how jump ropes bend in the wind?' A few literature searches later, he concluded that the answer was, 'not really.' Now, the two have solved the problem themselves."
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The Physics of Jump Rope

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  • by Fluffeh (1273756) on Wednesday November 02, 2011 @06:59PM (#37927184)

    I like this guy, he gets intrigued by some rather simple common things, then does the research to actually understand it, publishes it and closes the case. Here is another curiosity [sciencemag.org] that he has researched. Perhaps not amazingly useful at face value, but it may well help someone else with an idea or understanding of something else.

    • by errandum (2014454)

      His curriculum must be brilliant.

    • I agree. It kinda reminds me of Feynman's Wobbling Plate [wolfram.com].

    • by Anonymous Coward on Wednesday November 02, 2011 @07:28PM (#37927598)

      Reminds me of a guy named Richard Feynman who did some "meaningless" but fun physics research:

      Within a week I was in the cafeteria and some guy, fooling around, throws a plate in the air. As the plate went up in the air I saw it wobble, and I noticed the red medallion of Cornell on the plate going around. It was pretty obvious to me that the medallion went around faster than the wobbling.
                I had nothing to do, so I start to figure out the motion of the rotating plate. I discover that when the angle is very slight, the medallion rotates twice as fast as the wobble rate -- two to one. It came out of a complicated equation! Then I thought, "Is there some way I can see in a more fundamental way, by looking at the forces or the dynamics, why it's two to one?"
                I don't remember how I did it, but I ultimately worked out what the motion of the mass particles is, and how all the accelerations balance to make it come out two to one.
                I still remember going to Hans Bethe and saying, "Hey, Hans! I noticed something interesting. Here the plate goes around so, and the reason it's two to one is..." and I showed him the accelerations.
                He says, "Feynman, that's pretty interesting, but what's the importance of it? Why are you doing it?"
                "Hah!" I say. "There's no importance whatsoever. I'm just doing it for the fun of it." His reaction didn't discourage me; I had made up my mind I was going to enjoy physics and do whatever I liked.
                I went on to work out equations of wobbles. Then I thought about how electron orbits start to move in relativity. Then there's the Dirac Equation in electrodynamics. And then quantum electrodynamics. And before I knew it (it was a very short time) I was "playing" -- working, really -- with the same old problem that I loved so much, that I had stopped working on when I went to Los Alamos: my thesis-type problems; all those old-fashioned, wonderful things.
                It was effortless. It was easy to play with these things. It was like uncorking a bottle: Everything flowed out effortlessly. I almost tried to resist it! There was no importance to what I was doing, but ultimately there was. The diagrams and the whole business that I got the Nobel Prize for came from that piddling around with the wobbling plate.

      - Richard Feynman, Surely You're Joking, Mr. Feynman

    • by Reziac (43301) *

      Somewhat amusing that it takes scientific research to work out what every kid knows from observation, at least if they've ever used a double-length or very soft rope. Foot-timing can get downright tricky due to the slight lag in the middle.

  • Now I know. For the 10 days out of a year they go to gym, they get distracted by things like this!

    • by rolfwind (528248) on Wednesday November 02, 2011 @07:49PM (#37927822)

      Off-topic, but jump rope really is great exercise for both cardio, all-around conditioning, and coordination. A ton of boxers, past and present, do it, and it's my almost exclusive cardio. 12 minutes with a speed rope is more intense than 30 minutes jogging. Just have a decent surface to absorb shocks, and not hard like concrete. I used a wood pallet outside with a board on it as a cheap solution.

      • by GNious (953874)

        Weighted handles (metal bars) and a 4mm steel-wire for rope does wonders on exercising - just wear shoes, or learning will cost you a toe or two.

  • The duo boiled it down to a balance between two ratios: the length of the rope versus the distance between its ends, and the force of drag versus the inertia, or "centrifugal force," of the spinning rope.

    Don't you mean centripetal force, Science Magazine?! Hmm? HMM??!
    ( http://xkcd.com/123/ [xkcd.com] )

    • by shish (588640)
      I would think that they put it in quotes because they knew that it's technically inaccurate, but provides an easy to visualise mental model of the process
  • "Aristoff says, and if your goal is to set a speed record, "jumping rope at high altitude, where the air is less dense, could be advantageous."" What about the reduced levels of oxygen, would that not work against a person trying to set a speed record?

  • Didn't they prove that theory wrong? :-)
  • Love the way Americans call it a jump rope so as not to sound too girly :)

There is no royal road to geometry. -- Euclid

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