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Is it just translational motion or also rotational?

  1. Jan 31, 2006 #1
    In translational motion all parts of rigid body move with same speed and in same direction!I have a bit of problem between figuring out if particular motion is just translational or also rotational.

    If person slowly walks on top of gently rising hill, is his motion also at least partially rotational? If yes, why so? If not, why not ?

    Is any motion the path of which is (even if just a little bit) curved also rotational, or just rotational ?

    bye
     
    Last edited: Jan 31, 2006
  2. jcsd
  3. Jan 31, 2006 #2

    berkeman

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    If you graph the instantaneous motion of each body part as a function of time while climbing the hill, there will be a mix of translational and rotational motion. The net by the time you get to the top of the hill will almost 100% translational, and the net average of all the rotational motion will be very close to zero. Now if we had tank treads instead of legs to generate our motion, then there would be a net rotational motion in climbing the hill, right?
     
  4. Jan 31, 2006 #3
    Why will it also be rotational?
     
  5. Jan 31, 2006 #4

    berkeman

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    Look at how the legs move for each step. Thigh bone rotates up, shin bone rotates forward, thigh bone rotates down, etc.

    Doh! I just thought of a rotational component that will not average to zero for the person walking up the hill (or swimming or sitting still driving...). Can you think of what it is?
     
  6. Jan 31, 2006 #5
    I'd say peni* or boobs if there is no bra and they big enough to jiggle?o:)
     
  7. Jan 31, 2006 #6

    berkeman

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    LOL. Nope, those body parts don't rotate in a net way. Hint -- what I'm thinking of is rotating in your body even if you are sitting still.
     
  8. Jan 31, 2006 #7
    I have no idea,but I thought of something:

    I thought if there was a curve,no matter how small ( I don't mean small in a sense that you can step over it ) there is some rotation going on or perhaps even just rotation without translational movement? If there would be no friction and you'd be dragging up the hill(with small curve) a small box,would then perhaps movement be just rotational or... ?

    in any case,thanx for helping
     
  9. Jan 31, 2006 #8

    berkeman

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    I was thinking of blood circulation. Blood doesn't exactly circulate "around" the volume of the body, because arteries and veins are largely intertwined. But there are a few places where the separation is enough to give a net angular momentum to the blood flow in the body. And that angular momentum increases when you walk uphill.....moreso for some than others! :rofl:
     
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