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!

(Gases) How to get dU=(PdV+VdP)/(gamma-1) from U=PV/

  1. Feb 15, 2015 #1
    Hello I'm reading Feynman here: http://www.feynmanlectures.caltech.edu/I_39.html

    I'm having problems understanding how he turns equation 39.11 into 39.12.

    He does some U -> dU trick and he turns:
    [tex] U=PV/(\gamma-1)[/tex] into [tex] dU=(PdV+VdP)/(\gamma-1)[/tex]

    I don't understand this intuitively. Any help? Specificaly, how he expands PV into that (PdV+VdP) thing.
     
  2. jcsd
  3. Feb 15, 2015 #2
    Without reading the link, seems to me U is function in 2 variables: U=f(P,V)= P⋅V⋅const ⇒ dU=(PdV+VdP)⋅const.
     
  4. Feb 15, 2015 #3
    It looks like he is using the product rule for differentiation.

    Chet
     
  5. Feb 15, 2015 #4
    Ah yes of course! Thanks
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: (Gases) How to get dU=(PdV+VdP)/(gamma-1) from U=PV/
  1. PV^(gamma) = C (Replies: 9)

  2. PdV or Vdp (Replies: 13)

  3. Understanding H=U+PV (Replies: 17)

Loading...