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

Homework Help: Extremely quick question (MV calc/waves)

  1. Aug 11, 2004 #1
    My physics book gives this function for the displacement of a wave element oscillating in a longitudinal wave. Later on, they take the partial derivative with respect to time, like so.

    My question: Did my brain fall out, or is the negative sign in the second picture not supposed to be there? I'm open to either possibility right now :biggrin:
  2. jcsd
  3. Aug 11, 2004 #2


    User Avatar
    Science Advisor

    You are correct. You get one negative from the [itex]kx-\omega t[/itex] and another from the derivative of cosine.
  4. Aug 11, 2004 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Don't be. Understand your basics well enough that you know when something's right and when it's wrong. Your brain is doing good...just needs to feel more confident, and confidence comes from familiarity. :smile:
  5. Aug 12, 2004 #4
    Thanks for your replies!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook