Does This Trampoline Violate the Laws of Physics?

By Julianne Dalcanton | December 17, 2012 5:46 am

Late last week, I ran across a spectacular video of a man being completely awesome:

The video shows Christophe Hamel jumping/falling/hurtling off of walls, landing on a trampoline, and then bouncing up to land back on top of the wall — sometimes in a handstand in case there was a risk you wouldn’t be impressed enough otherwise [seen at 1:50+].

My first thought on seeing this video was “It’s gotta be really hard for his mom to watch this.”

My second thought was, “Is it really possible for a trampoline to conserve energy that well?”

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, leading to the following:

If you’re talking about a bouncing ball, and you lose some energy deforming the ball during the bounce, no harm, no foul.  But, if you’ve just fallen 2 stories and are trying to bounce back up to the same height, then you’d better conserve every last possible bit of energy you possibly can.

I’ve spent more time than I care to admit watching this guy, trying to figure out if trampolines are really that efficient at changing a person’s direction without significant energy loss.  I think that to first order, yeah, they must be.  At first I thought that he might be extracting energy out of his muscles at the turnaround, but in most of the tricks, he’s pretty much dead dropping on his curled back, not pushing off with his legs.  My second thought was that maybe he was extracting energy from his initial rotation, but in a number of the tricks he’s coming back with more rotation than he left with (although frequently in a tighter tuck, so it’s not clear what’s actually happening with his angular momentum — i.e., I’ve watched, but have not done math).

The one thing that has convinced me that he does not have an invisible jet pack is that he doesn’t really come back to exactly the same height.  His feet do (eventually), 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!).  Here’s a couple of examples right from the beginning of the film, with the takeoff on the left and the return on the right:

And another showing an example of the extra vertical takeoff (a bit trickier to see in the stills because of the perspective, but it’s clear in the video that he’s jumped upwards):

I’m relieved that energy conservation is still with us, despite this man’s very fine attempts to do away with it.

CATEGORIZED UNDER: Science, Sports
  • Guest

    I believe that because the gymnast is starting from the same Initial point every time he drops in to the trampoline at the same acceleration of (-9.8m/s^2) with the positive Y being him going away from the ground. That being said the trampoline is not defying the laws of physics the trampoline just gives enough Force acting on to the gymnast to accelerate him back to what looks like his original initial position but is actually just decreasing at a very slow rate.

  • http://www.facebook.com/robby.rodriguez.524 Robby Rodriguez

    I believe that because the gymnast is starting from the same Initial point every time he drops in to the trampoline at the same acceleration of (-9.8m/s^2) with the positive Y being him going away from the ground. That being said the trampoline is not defying the laws of physics the trampoline just gives enough Force acting on to the gymnast to accelerate him back to what looks like his original initial position but is actually just decreasing at a very slow rate.

  • http://www.facebook.com/peter.fred.148 Peter Fred

    Doctor: How do you get around the fact that Newton’s Law of Universal Gravitation proposes that gravity is a perpetual motion machine? The law says that there is a force where the the big mass attracts the little mass. You cannot have a force without a source of energy. Having something that creates a force with no energy is a perpetual motion machine. A ball an infinite distance from the earth falls towards the earth. Where does the energy come from that creates the force that drives the ball towards the earth? Do not give me this convoluted nonsense that energy comes out of the vacuum to create the force that drives the ball towards the earth. Face “the horror, the horror” that Newton’s Law violates the law of conservation of energy. I am getting 99% weight loss with my heat-based gravity theory. So maybe it is the heat from the sun and not its mass that is responsible for the orbital motion of the planets around the sun. http://vixra.org/abs/0907.0018

  • http://www.facebook.com/stephen.anderle Stephen Anderle

    Some of those looked like they could be reverse run, but not all.! I think it’s not so much conservation of momentum but added energy being multiplied several times over by a very good trampoline. It takes very little added movement of shoulders arms legs to add quite a bit of energy of motion when everything is applied at the right time. I used to see how high I could get on one when I was a kid till I got scared of the height!!! All you have to do is stand very still and straight and push with your toes and you get very higher very quickly!! He is very good and coordinated!

  • http://www.facebook.com/kate.asam Kate Asam

    These have been around for a while now. Take a look at Cirque’s La Nouba (there should e some clips of it on Youtube), the trampoline performance is one of the star events. Judging from one or two of the clips in the video, I wouldn’t be surprised if he’s one of their acrobats.

  • Reese Houser

    i really enjoyed
    this article,because this was me many years ago,and to a certain degree,this
    is who i am today

    http://www.brilliantpapers.com

  • ichkanns

    Written by someone who has never been on a trampoline? If this were really a problem then upon getting on the trampoline you would never get higher than your initial height. You use your legs to jump each time and that is how you get higher. I figured this was pretty common knowledge…

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