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Harmonic Motion and strobe

  1. Mar 1, 2005 #1
    Harmonic motion is when an object pretty much goes back and forth, right?

    Also, what does the word 'strobe' mean? I once heard a member here say that if our eyes worked like a camera and took a picture 60 times a second that a light that flashed 61 times per second would appear to strobe at one flash per second. Why is this? What if the light flashed at 38 times per second?

    Also, what does it mean for one thing to be 'in harmony' with another object?
    What does it mean to be 'in phase'?

    This is just an area I feel I'm lacking in knowledge so I'm asking for help.
  2. jcsd
  3. Mar 1, 2005 #2


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    There is a little bit more to it then that. Consider a point on a rotating circle, now if you rotate the circle till all you see is the edge, or a line, the way the point moves along that line is SMH. It will move faster in the middle then at the ends. This predictable and repetitive motion is essential to SMH.
    A strobe is simply that, a light source which flashes on and off at a regular rate.
    I have no clue.
    Suppose you had two circles with moving particles as I described above, if the the points on each circle are at the same place (both at an the same end point moving in the same direction, both at the center, moving in the same direction, they are said to be in phase. On the other hand if one is in the center while the other is at the end they are out of phase.
    I hope this is of some help.
  4. Mar 1, 2005 #3
    Say object A moves in a random pattern but repeats this pattern once every 4 seconds.
    Say Object B moves in another random pattern but repeats it every 8 seconds.

    Will object A be 'in phase' with object B at t=8 seconds?
    If object B is started in motion 2 seconds before object A, will they be in phase 2 seconds after that?
    Does being 'in phase' mean that two things are at the same spot in their individual cycles? (i.e. 1/4 done)
    Does it mean that they are at the same point in the same cycle?

    Finally, by SMH do you mean simple harmonic motion?
  5. Mar 1, 2005 #4


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    I have no idea. SHM is not random motion.
    Yes. waveforms with different frequency do not have constant phase relationship.
    Who me,.. dyslexic??? :uhh:
    Last edited: Mar 1, 2005
  6. Mar 1, 2005 #5
    I didn't say random motion. I said random patterns. It's possible for the path of motion to be random but the motion itself still predictable. What I mean is, for instance, look at a trail going through a thick woods. It will wind all over the place somewhat randomly, yet if a jogger goes the exact same route over and over the motion will be completely predictable (cyclical).

    Does harmonic motion only occur in geometric shapes like circles and sine waves?
  7. Mar 1, 2005 #6


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    That could be termed Periodic motion, but it is not SHM.
  8. Mar 1, 2005 #7


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    When it comes to oscillations,it's more important to consider the frequency or the period to be constant.The amplitude may vary (damping),but the frequency better stay constant.

    As for harmonic,usually yes,but keep this adjective out of the realms of mathematics,because there it means something else...

  9. Mar 1, 2005 #8
    What does it mean in mathematics? I'm assuming it's calculus, correct?

    Frequency and period are pretty much the same thing, right? At least, interchangeable? What I mean is, they are both different ways of measuring a "how often" variable?

    Why must frequency remain constant? Does it always remain constant? Is this how different wireless devices keep all their information streams separate?
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