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!

Homework Help: What is the pressure in the middle of a vortex?

  1. Dec 8, 2013 #1
    1. The problem statement, all variables and given/known data
    The expression below describes a potential vortex in polar coordinates. What is the pressure p in the middle of the vortex, i.e. at radius r=0, relative to the surroundings?


    Does anyone have any explanation to this answer? Why is the pressure infinite? And why is it a negative? I've been thinking about this for so long and can't come up with any explanation...
  2. jcsd
  3. Dec 8, 2013 #2
  4. Dec 8, 2013 #3

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    The minimum force per unit area is 0. The - or + sign simply denotes the direction in which the force acts on a unit of area which depends on which direction you choose to be +.

    In a vortex, the swirling mass of air is kept from flying outward by the external pressure. So the difference between the vortex pressure and the external pressure supplies the centripetal force that the swirling molecules need in order to keep from flying outward. If the molecules swirl fast enough for a given radius of curvature, the centripetal force can be equal to the external pressure (atmospheric pressure) and the vortex pressure is then 0. It cannot go any lower than that.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted