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Gyroscopes feel lighter when spinning

  1. Jun 6, 2007 #1
    Ok...I cannot remember where I had seen it....I believe it was in a science book in high school because I remember a picture being associated with it.

    It went something like this: Some famous physicist/scientist had a very heavy gyroscope at the end of a long metal rod. He could not lift this, even if he was lifting from the center of gravity. When he got the gyroscope spinning fast enough, he was able to lift it from the end as well as the middle.

    The article never talked about this any farther and I can't find any information to support or debunk this claim. My physics brain says that this can't be true.

    What do you guys think?
     
  2. jcsd
  3. Jun 6, 2007 #2

    FredGarvin

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  4. Jun 6, 2007 #3
    That's a really neat video, but it doesn't actually answer my question.

    The article that I read claimed that the gyro could not be lifted before spinning, but after spinning. Maybe the video does answer the question, but all that I saw it prove was that it changed the center of gravity, in a way. It would be hard to lift those 18 lbs by grasping the end of the rod if it was not spinning, but easier when it is. If that boy could not have lifted that gyro before it was spinning, then it would explain it. But I would be willing to bet he could lift that.

    Does this make more sense?
     
  5. Jun 6, 2007 #4
    I've seen the same claim about fast spinning bodies that they become ligher and even antigravitate. Some guy was claiming that's how the UFO fly and even claimed that the Nazi had projects during the World War II to develop such flying machines.

    Classical Newtonian physics and GR disagree. Moreover, according to GR, the fast spinning body is a tiny bit heavier than the nonspining because the rotational kinetic energy adds to the gravitational mass (and hence to the acceleration mass).
     
  6. Jun 6, 2007 #5

    rcgldr

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    When spinning, and precessing about one of it's ends, the gyroscope behaves as if it was hanging by (or standing from) that same end. As shown in other demos from that same web site, there's no angular momentum with respect to the precession movement.

    http://www.gyros.biz/lecture/wmv/8.wmv
     
  7. Jun 6, 2007 #6
    why?:confused:
     
  8. Jun 7, 2007 #7

    rcgldr

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    A link to an article that helps explain "why":

    http://www.gyroscopes.org/how.asp

    The wheel in the gyroscope has a lot angular momentum. It's complicated but a torque force applied to a gyroscope results in a movement reaction that is about 90 degrees out of phase with the torque force. A yaw force results in a roll reaction and vice versa. IN the case of helicopters, the control stick is set 90 degrees out of phase to compensate for this. If the pilot pushes the stick forwards for a change in pitch, the rotors will cycle 90 degrees out of phase through a pattern that creates a torque force in the roll direction, but the result is a change in pitch. Like wise a roll command is translated into a pitch torque thrust, which results in a roll reaction.

    Here is that link to the gyroscope lectures / videos from 1974:

    http://www.gyroscopes.org/1974lecture.asp

    Number 18 attemps to show what's going on:

    http://www.gyros.biz/lecture/wmv/18.wmv

    You can start with wiki and go on to the other links from there:

    http://en.wikipedia.org/wiki/Gyroscope
     
    Last edited: Jun 7, 2007
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