1. Not finding help here? Sign up for a free 30min 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!

Finding pressure with given radius

  1. Sep 5, 2011 #1
    1. The problem statement, all variables and given/known data
    http://img585.imageshack.us/img585/613/labnotebookq.gif [Broken]

    Uploaded with ImageShack.us
    A Test tube filled with water i being spun around in an ultracentrifuge with constant angular velocity, w (w = omega). The test tube i slying along a radius and revolving in a horizontal plane. The free surface of the water is at radius r(0) (with smaller parenthesis) as shown

    a) show that the pressure at any raidus r within the tube is given by: P=1/2 (row)(omega)^2+P(atm)

    b)suppose that w=3.8x10^5 rad/s and r(0)=10cm, what is pressure at r=13
    Does it matter whether it's gauge or atmospheric pressure?

    question, is it asking whether gauge pressure and actually pressure are the same?

    2. Relevant equations
    centripetal accleration =v^2/r = r(omega)^2
    Pressure= P(atm) + (row)*g*h
    where row is density, g is gravity (or acceleration in this case), and h is dept
    density = (row) = m/V = mass over volume



    3. The attempt at a solution
    took simple approach
    a= r(omega)^2

    and used this "a" (acceleration) as"g" (gravity)
    and r-r(0) (since that's the dept of watr) as h
    so using Pressure= P(atm) + (row)*g*h
    P= P(atm) + (density of water)*r*(omega)^2*(r-r(0))
    in symbols :P
    P= P(atm)+p*r*w^2(r-r(0))
    but this doesn't match the answer ;)
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 5, 2011 #2
    This is how I would start, does this work?
     

    Attached Files:

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Finding pressure with given radius
Loading...