Dot Physics

Here is the deal. Why would you put a lot of effort into explaining something wrong? I just don’t get it. Wouldn’t it be easier and better to just not say anything? The particular show I am ranting about is the 2008 Punkin Chunkin on Discovery (I think). Fairly ok show, but they should have left the science out. The part that made me speak out was when they were talking about the different types of punkin chunkers. They have:

  • Compressed air
  • Catapult
  • Trebuchet
  • Centrifugal Force Machine

To explain these devices (the physics behind them), the show brought in the big guns. Let’s bring in an MIT physics professor that has won a Nobel Prize. That should do it, right? Here is their animation of a centrifugal force machine.

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As they show it spinning, they freeze on the release point. Here it is:

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So, if you want it to be “shot” at around 30 degrees, this is where you should release it. Right? No. I don’t mean to say this in a bad way, but I think some 8th graders could even see that this is wrong. First, which direction is the pumpkin moving at this instant?

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The device is exerting a force on the pumpkin to keep it moving in a circle, when that force is removed, the pumpkin will continue moving in the direction it was moving. To Further prove their point, the show includes this other diagram.

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I am not sure what they are trying to show. Is that the velocity (no) or maybe the centrifugal force. But the centrifugal force is a fake force if you want to be in the rotating frame of the pumpkin. If you want more about the centrifugal force, here you go.

Ok, one more complaint. Here is basically what the MIT prof said about the centrifugal machine. (If there is a large demand, I will list his name – he doesn’t need protecting since he got paid to do the show and he has a nobel prize).

“the basic idea in a centrifugal force machine is to accelerate a body by taking it around a circle many many times. Each time, it gets a little bit faster. When you decided it is fast enough, you somehow release this force….”

Maybe this isn’t too bad, but when I saw this, I didn’t like it. It seems he is saying there is some type of force stored up as though it were energy. And then that force (energy) is released. Looking back at it, maybe it is ok.

The science in this show was a distraction, but the pumpkin launchers did inspire me. Another punkin chunkin post will come soon.

Comments

  1. #1 Uncle Al
    October 31, 2009

    Given the launch forms of military artillery… compressed air is the way to go given a large enough, high enough pressure, fast enough flow, fast valve setup. No example I have seen has an anywhere near fast enough large bore valve. Most are innocent of gas flow, including 180 degree elbows reservoir to barrel. A thin inner barrel coating of Crisco will work wonders, as would modest rifling re British muskets vs. Kentucky long rifles.

    Ballistic pumpkins should be gorged on calcium as they grow to harden their substance. They should also have suppressed polygalacturonase re the Flavr Savr tomato (pCGN4109a and pCGN1436 hybridized antisense RNA) to stay firm when ripened.

    The Japanese could kick redneck butt with a modest directed effort.

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