Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Amplitude Entrainment?

  1. Jun 25, 2010 #1
    I am so happy to have found this forum. I am trying to understand a concept about frequency entrainment. I remember reading many times that two different, but similar vibrating bodies can lock into a constructive interference regarding their frequencies, however I thought that their amplitudes were completely independant of that.

    However recently, a self proclaimed physics affcianado told me that when two similar vibrating bodies come into contact, the higher amplitude vibrating body will cause the more “quiet” vibrating body to take on its amplitude. In other words, the louder vibration wins. Is this correct? If so, is there a name for this phenom?
  2. jcsd
  3. Jun 25, 2010 #2
    In doing some online research I found this image that essentially explains what my friend is saying. http://www.flickr.com/photos/44173456@N03/4734783316/" [Broken]

    What do you think? Is it bunk?
    Last edited by a moderator: May 4, 2017
  4. Jun 26, 2010 #3
    No info on this?
  5. Jun 26, 2010 #4
    Never heard about that, and I can't think of any mechanism to give you that phenomenon. You can have resonance if you force an oscillator with its natural frequency, of course. Maybe you're talking about that. Can you give a more physical example?
  6. Jun 26, 2010 #5
    I really can't give an example becasue this is all he told me. I was confused by it.

    Can you explain this a bit more please?
  7. Jun 26, 2010 #6
    The soprano lady who can break glasses with her voice... All oscillators have a natural frequency, at which they will oscillate if perturbed and then left alone. Now, if you force an oscillator with its natural frequency, its amplitude will grow with time (and eventually may break up, like the glass). This can be achieved if you have a second oscillator with the same frequency, which is oscillating by itself, but which is somehow linked to the first one.
  8. Jun 26, 2010 #7
    Ah yes! Thank you. Do you have a link or book you can recommend where I can do some more reading on this specific subject?
  9. Jun 26, 2010 #8
    There is a chapter in first volume of Feynman's lectures on physics (all praise be given to him) ;) , that's quite nice. Of course, just typing "Resonance" in wikipedia or google can give you lots of info.
  10. Jun 30, 2010 #9
    OK, I will get a copy of that book.

    Here's an email I received from him regarding this "Law of Resonance" when I asked for an example. Its not really an example, but he explained a bit more. I am not finding this anywhere in my own research regarding the science of physics:

    "When one system encounters another similar system, their vibrations must come into a state of resonance (harmonic vibration). This law also states that the weaker amplitude vibration will be influenced by and change to match the stronger amplitude vibration."
  11. Jan 12, 2011 #10
    Is this a principle of physics found anywhere? I have searched quite a bit and am not finding it. TIA!
  12. Jan 29, 2011 #11
    How about the Principle of Entrainment? Can someone state it for me?
  13. Jan 30, 2011 #12
    This use of the term 'entrainment' is about circadian rhythms and really belongs in the biology section, which may be why you have seen almost no takers.

    I am not a biology specialist so cannot help further.
  14. Mar 25, 2011 #13
    So this does not occur on physics at all?
  15. Mar 25, 2011 #14


    User Avatar
    Science Advisor
    Gold Member

    There is no physical law that I am aware of whereby two oscillating systems come into contact with one another and the weaker oscillator takes on the characteristics of the stronger oscillator. There isn't even any guarantee that they would constructively interact.

    Perhaps your friend is using the wrong terminology or just generally doesn't know what he is talking about?

    Resonance occurs - all the time. However, resonance is not what you are describing. it could be that your friend is thinking of resonance and just doesn't understand it as well as he thinks he does.
  16. Mar 26, 2011 #15


    User Avatar
    Science Advisor
    Homework Helper

    Effects like this can occur in nonlinear systems, where the natural frequency depends on the amplitude of vibration for some reason.

    Every real-world system is nonlinear to some extent, though the nonlinearity is often small enough to be ignorable.

    But the graph you posted could be nothing more than forced response of a linear system. In other words, some energy from the "large" oscillator is getting into the "small" system and shaking it around at the same frequency, once the the initial transient response (at a slightly different frequency) has died away. It's hard to give any "explanation" for it without knowing what system (either physical or mathematical) the graph is showing the response of.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook