1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculate the force on a squre plane exerted by a pressure

  1. May 7, 2014 #1
    Hi, I have a situation like the following and I need to calculate the force as well as the sound pressure exerts on a rectangular object.

    If I have a sound source which is mapped on a 10cm x 10cm square plane, and the sound source generates for example 20Pa (N/m2) . The generated sound travels and is reflected by another plane with the dimention 100cm x 100cm, and it comes back into its own square plane(10cm x 10cm).

    As far as I know, there will be a force exerted on the 10cm x 10cm plane by the reflected sound pressure.
    Assume the distance between 2 square planes is 1cm. Then how large that force would be.

  2. jcsd
  3. May 7, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Well if you know the pressure wave for the sound, and you know the area he pressure is exerted over, then the definition of pressure would be a good place to start.

    What do you need to know for?
  4. May 7, 2014 #3
    Thanks for the response @Simon Bridge.
    I guess the force exerted on the 10cm x 10cm (let call it P1 with the area A1) by the reflected sound would be a multiplication of the sound pressure of the reflected sound wave and area A1.
    But the problem is:
    The sound source is generating the sound wave continuously, so I think:
    1) there may be a superposition between the reflected wave and the new generated wave. But I'm not sure and don't know how to calculate the final sound pressure at P1 in case it exists.
    2) I think the size of the reflector 100cm x 100cm (let call it P2 with the area A2) also has some influence on the sound pressure or the exerted force on P1. But I don't know how is the relation between them.

    I couldn't find any information for this problem.
    Thanks very much

  5. May 7, 2014 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    1) there will - the exact solution depends on how the reflector responds to the pressure.
    There will also be turbulence. However - it's still a good start off the information you have provided.

    2) The geometry of the reflectors will be important - all reflectors will have an impact.
    Note: sound does not produce a constant pressure.
  6. May 8, 2014 #5
    Thanks @Simon Bridge.
    As you said, the geometry of the reflector has an impact on the reflected sound wave. How about the size of the reflector. I think it should be larger than the size of the generator plane, but how much larger should it be, and is there any difference if it's 10 times larger or 100 times larger than the generator plane.

    Could you please do me a favor?
    Assume that we have a system as described above. Could you please give me an example with some numbers, so that I can have a better understanding as well as know how to calculate the force exerted on the plane P1, which has the sound generator, due to the reflected sound wave.

    Because I want to levitate the plane P1 using the force exerted by the reflected sound pressure to cancel the gravity force. Supposed that the reflector P2 is fixed and the plane P1 has a light weight e.g 50gram. ( If there is any need parameter missing, please just give it some value).

    I really appreciate for your help. Thank you very much.
  7. May 8, 2014 #6

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    There are plenty of resources for acoustic levitation.
    Use those words as a search term.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook