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anonymous

  • one year ago

Simple harmonic motion question

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  1. anonymous
    • one year ago
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    it said that the particles acceleration is proportional to displacement but sign is opposite? What does that mean? I know that the displacement graph looks like this and the acceleration graph looks like this for SHM ....|dw:1441423084425:dw| The textbook also said that acceleration magnitude is zero when displacement is zero (which for velocity is the max) and acceleration is max when particle at the crest or trough (for velocity is 0). Is that what it means by sign is opposite?

  2. anonymous
    • one year ago
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    @zepdrix @UnkleRhaukus

  3. zepdrix
    • one year ago
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    |dw:1441436026318:dw|

  4. zepdrix
    • one year ago
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    Yes, it means opposite sign :) In this example, I was trying to show that if you're displaced an amount \(\large\rm x\) from equilibrium, then the acceleration is \(\large\rm -x\) at the same time. I'm not so good with the physics, it would be a lot easier to explain this using calculus lol oh well!

  5. IrishBoy123
    • one year ago
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    the key to shm is the restorative force. All proper shm starts with the equation F = -kx the restorative force F is proportional to displacement x but acts in the other direction [hence - sign], ie back toward the origin/point of equilibrium everything everything everything follows from that.

  6. Michele_Laino
    • one year ago
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    the harmonic motion can be modeled by this function: \[\Large x\left( t \right) = A\cos \left( {\omega t + \phi } \right)\] we can set \( \Large \phi=0 \), without loss of generality, so we can write: \[\Large x\left( t \right) = A\cos \left( {\omega t} \right) \qquad \qquad (1)\] of course, the constant \( \large A \) is the amplitude of our motion. Now taking the second derivative with respect to time of the last equation, we get: \[\Large \ddot x\left( t \right) = - A{\omega ^2}\cos \left( {\omega t} \right) = - {\omega ^2}x\left( t \right) \qquad (2)\] As you can see, your graph are the graphs of the equations \( (1), \; (2) \) respectively @dareintheren

  7. Michele_Laino
    • one year ago
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    neglecting the scale factor \( \Large \omega^2 \), of course

  8. IrishBoy123
    • one year ago
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    and from \[\Large \ddot x\left( t \right) = - A{\omega ^2}\cos \left( {\omega t} \right) = - {\omega ^2}x\left( t \right) \qquad (2)\] note that \[\Large m\ddot x\left( t \right) = F = - m{\omega ^2}x\] the **restorative** force

  9. IrishBoy123
    • one year ago
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    and just to be totally clear, the maths follows the idea of a restorative force, and not the other way round:p

  10. anonymous
    • one year ago
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    Thank you guys for responding, more clear now, I can only medal the best one, but all was good!

  11. IrishBoy123
    • one year ago
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    see this too http://openstudy.com/study#/updates/55daa36de4b02663346bfab3

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