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This trampoline routine will have you doubting the laws of physics

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The acrobatics in this video are just insane. Insane enough to make you question the laws of physics, really. I mean, could these trampolines really be conserving so much energy as to allow Christophe Hamel (he's the one soaring all over the place) to return to what appears to be the same altitude after basically every jump?

In a word, yes; this video is real — but incredulity is still in ample supply. Over at Cosmic Variance, Julianne Dalcanton lays out the basis of our amazement:

Here's the problem. In introductory physics, you learn that when something falls in a gravitational field, it turns gravitational potential energy into kinetic energy (i.e., falls down, goes faster). If that same something then bounces, it proceeds to do the reverse. To get back to exactly the same height, there cannot be any energy lost from the object - no energy lost to air resistance, or to internal motions in the object. However, in pretty much every aspect of our real world experience, we know that this perfect energy conservation doesn't occur.


And yet, Hamel (and plenty of other acrobatic, wall-trampolining crazy people) pulls it off. How? According to Dalcanton's (admittedly non-mathematical) assessment, the trick isn't extra energy input from Hamel's muscles, or from rotating on his descent, but from the way he positions his body just before each fall — and the fact that his center of mass is just slightly lower at the peak of each return-ascent:

His feet do (eventually) [return to their initial height], but he usually starts the trick from a tall position, frequently with an arm stretched vertically, or with a jump to get some extra height. Then, when he comes back up, he's frequently in a tuck or a dive, such that his center of mass is indeed lower than when he took off (though granted, not by much!).


See Dalconton's full analysis, complete with screenshots, over at Cosmic Variance.