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Angular Momentum

  1. Sep 1, 2008 #1
    This is the basic Wiki definition of angular momentum. I was wondering if someone "perhapse a teacher" could put this into words I understand. I know that this can be translated into a more understandable words.

    I firmly ask that you do not tell me to wait until I go to college to study this. I know that I can learn it if I try, and ask enough questions.

    Lastly, i'm sorry for my spelling errors. I usually use my cell phone which has spell check. I currently am on my computer though. Please excuse my spelling.




    I'm sorry. Please let me explain what I know about angular momentum.

    I know that angular momentum is what makes a ice scater spin faster as she brings her arms in and gets lower to the ground. I know that as a star or planetoid becomes more dense, it gains speed, and as it explands, it loses speed. I also know that the our solar system has slowed down the rotation of the sun due to angular momentum.
    Last edited: Sep 1, 2008
  2. jcsd
  3. Sep 1, 2008 #2


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    Homework Helper

    The example of a figure skater is conservation of angular momentum. If an object or system of objects is not acted upon by an external force, then angular momentum is conserved. As mentioned in the wiki article, angular momentum is the product of radius times speed. If only internal work is done, then any change in radius requires an inverse change in speed. For example, if the radius is decreased to 1/2 of it's original length, then speed is increased to twice the original speed. This change requires internal work to be done, because angular kinetic energy changes even though angular momentum remains the same. In the figure skater example, internal work is done when the skater pull in her arms, and the amount of work done determines the increase in angular kinetic energy (rotational energy).

    Note that the figure skate example only works in the idealized case where there is no friction from the ice. In real life, the rate of rotation decreases over time because friction in the ice applies an external torque to the skate.
  4. Sep 1, 2008 #3


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    Staff: Mentor

    How about this? In the passage you quoted from Wikipedia, tell us the first word you don't understand, and someone can try to explain it, or at least point you to places where you can read about it. Then we can move on to the next word you don't understand, etc.

    It's kind of hard to put things in understandable terms (for you) if we don't have any idea of what, specifically, you don't understand, and what you're capable of understanding with your current background.
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