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Do these trampoline feats violate the law of conservation of energy?

No. Nobody violates the law of conservation of energy, just like nobody expects the Spanish Inquisition. But it does seem like Christophe Hamel rises to a greater height than from where he jumped.

Julianne Dalcanton explains how the illusion is created.

One thing to bear in mind is that it is the center of mass of an object that cannot rise higher than the point from which it was dropped. In a flexible object like the human body, you can shift its center of mass by raising your arms, curling up in a ball, crouching, etc. Since observers tend to focus their attention on the head of the person they are watching, this can create gravity-defying illusions by ballet dancers and basketball players because the trajectories of their heads are flatter than one would expect for a projectile, and thus they seem to ‘float’ in the air.

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Another way to rise higher than where one started from is to use one’s muscles to convert some of the body’s internal energy into overall kinetic energy, which is what we do when we jump up from a crouching position and what Hamel is doing when he sometimes pushes upwards off the side of a wall on his rebound.

One thing is clear and that is that very little energy seems to be dissipated by the trampoline itself, much less than I would have expected. Another is that Hamel’s nerve and skill are impressive.

Comments

  1. Jean says

    As a former gymnast (and as you can see from others commenting where you linked), what looks like very high efficiency of the trampoline is actually skill and hard work from the athlete. It may not look much from the outside especially when looking at someone who’s highly skilled but there is a lot of work done and energy spent to perform those tricks.

  2. Nepenthe says

    But he’s not (generally) pushing off the trampoline, he’s contacting it with his butt. So how is he expending energy on the way up?

  3. Jean says

    The core muscles are working by relaxing and tensing at the right time as well as flexing and extending at the hips and knees to project the legs up at the right time. And it doesn’t have to be movements with a big amplitude to make a big difference.

    You also have to realise that the twists and flips done come from similar actions and do also contribute to gain some height.

    And it’s not his butt that is contacting the trampoline but the back. So there are quite a few big muscles that can be used.

  4. Jean says

    As a side note that could be relevant here, a lot of the indoors shots in the video are from the Quebec City circus school which is in a converted catholic church. In the last 50 years or so, the province has gone from having the catholic church involved in all aspects of the Quebec society to what is probably the most secular region in North America. So there are quite a few churches that have been converted to other uses (mostly condos).

  5. Suido says

    Another former gymnast checking in, I’ve also spent considerable years since as a coach (beats working part time in retail, like most students :P ).

    Agree with Jean, there is a lot of work done by the trampolinist to generate extra bounce – using core muscles as well as timing of limb movements. When bouncing on your feet, timing your arm swing is critical for helping attain maximum height. When bouncing on your back your legs can perform the same role by kicking upwards. This is how you can bounce on your back indefinitely – you are contributing more energy to the system with your muscles, enough to counter the energy dissipated by the trampoline.

  6. Suido says

    PS The illusion regarding centre of mass as explained by Mano is best seen in the very first trick, the side somersault over the concrete edge. It seems like he pauses in the air as his head stops ascending and his body rotates over it.

    The effort put in by his legs is best seen at 1:45, you can see him kick his legs apart and upwards, timed to perfection with the trampolines spring action.

  7. Suido says

    PPS The latest Cirque du Soleil to come to Australia (Ovo) had a group dressed as grasshoppers doing tricks like this on a row of trampolines at the base of wall. Absolutely awesome.

  8. jamessweet says

    I was puzzled that people were puzzled. IANAGymnast, but after all you do have muscles in more parts of your body than just your legs :p It’s amazing that people can do this, and impressive to watch, but never for a minute did “How on earth does he do that?” cross my mind (well, aside from, “How on earth does he get himself to practice so fucking much and be in such good shape?”)

    As far as the title of the video calling it “new”, I did find that puzzling… What seems to be new here is that he’s taking a pretty long-standing circus routine (albeit a highly impressive one that he does very well) and doing it “in the wild”, which is pretty cool but not exactly a “new sport”.

  9. baal says

    That looks like so much fun! (and a seriously hard work out)

    I used to do flips and rolls as part of “how nt to get killed while doing martial arts”. It was easily the most tiring part of any training session. Watchers occasionally commented that they didn’t understand why the stuff that looked easy was the only time we panted.

  10. Doug Little says

    I wish I had of learned how to tumble when I was growing up, unfortunately I grew up in a small country town on the south east cost of Australia and gymnastics wasn’t an option. I think gymnasts pound for pound are some of the strongest athletes on the planet, they always amaze me.

  11. left0ver1under says

    In a flexible object like the human body, you can shift its center of mass by raising your arms, curling up in a ball, crouching, etc.

    Another difference is that static objects like balls cannot exert force themselves. A human can use legs, arms or even the back to exert force and add energy to a bounce (or remove energy – the legs are used as shock absorbers to stop bouncing) . Energy can be added to the system by the gymnast without being visible from the outside.

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