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Thread: Please help me with velocity :-(

  1. #1 Please help me with velocity :-( 
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    Its for my physio class but it does have a physics component too it. Can someone please help me.

    Can some one please help me calculate velocity? I placed my question in the "Biology" section of this forum with a thread called "Calculating Velocity"
    . It has a pretty intensive math/physics component. Please help. I've been thinking about for 4 hours now. Not sure where to really post. Thank you!

    http://www.thescienceforum.com/Calcu...ity-27023t.php


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  3. #2  
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    Nine centimeter arm is swinging 2.6 m/s, how fast is 70 cm arm?


    Or is it biologically correct that arm that has been amputated
    at the muscle insertion point moves at the velocity that the
    muscle shortens?


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  4. #3  
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    What if we used 2.6m/sec for all points ( 70, 61, and 9)? How could I figure out the velocity?
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  5. #4  
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    Someone wrote me this:

    Make yourself a diagram of this, and assume that the "man" keeps his arm straight while throwing the ball. (If he bends his elbow, all bets are off.) You'll see that you have a couple of similar figures: one with the portion of the arm between the socket and the point of attachment to the muscle, the other from the socket to the ball. One side of the smaller one (the muscle) is shrinking at 2.6 m/s. Given that, figure out how fast the ball is moving. Remember how similar figures work (sophomore geometry).

    I'm still trying to digest it.
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  6. #5  
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    Let's say there is a 9 cm arm. Now somehow this arm grows 8 times longer.
    This new arm throws balls 8 times faster than the old one.
    Quite simple.
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  7. #6  
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    Quote Originally Posted by searchme
    Someone wrote me this:

    Make yourself a diagram of this, and assume that the "man" keeps his arm straight while throwing the ball. (If he bends his elbow, all bets are off.) You'll see that you have a couple of similar figures: one with the portion of the arm between the socket and the point of attachment to the muscle, the other from the socket to the ball. One side of the smaller one (the muscle) is shrinking at 2.6 m/s. Given that, figure out how fast the ball is moving. Remember how similar figures work (sophomore geometry).

    I'm still trying to digest it.
    1. You may safely ignore jartsa. His next relevant correct post will be his first one.

    2. To get any real help you will have to provide some sort of diagram of the bones and muscle connections. This is basically a problem in geometry and determing both rotational and translational velocities. There is some reference in your problem statement to muscles of the forearm, so one might suspect that what we have is two motions to combine, the motion of the upper arm created by the shoulder muscles combined with the motion of the forearm and wrist created by the muscles of the upper arm and the forearm.

    3. You ought to be able to model the kinematics with a couple of rigid members representing bond and a couple more members of variable length representing muscle. Once you have that the hint regarding using triangles should make a bit more sense to you.
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