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: Finding the volume

  1. Dec 26, 2005 #1
    Is there a guideline that one can follow when finding the volume of a solid obtained by revolving over a region. The three methods that i know are disk, washer, and shell method. But i dont know when to apply which method. My book doesn't explain it clearly. If anyone could help me with this, i will appreciate it. Thanking you, and have a safe and wonderful holiday.
  2. jcsd
  3. Dec 26, 2005 #2

    Depends on the symmetry of the object and how it is rotated, but you can apply both if you want. Actually, this is a good exercise...

    Check out :

    http://mathdemos.gcsu.edu/shellmethod/ I used this website when i tutored students in college. I recommend it...
    disk and shell method

    Last edited by a moderator: Apr 21, 2017
  4. Dec 26, 2005 #3


    User Avatar
    Science Advisor
    Homework Helper

    You could use Pappus' Second Theorem.
  5. Dec 27, 2005 #4
    thanks marlon, i will check it out.
    Last edited by a moderator: Apr 21, 2017
  6. Dec 27, 2005 #5
    I am not familiar with Pappus' Second theorem. We never learned that theorem. Thanks
  7. Dec 28, 2005 #6
    You use the disk method when you know you can distinquish a inner and outer fuction, and want to produce a glass china.
    To use the waster method, you are trying to find many A(x), to do a intergral of many A(x)dx s. you see, A(x) can have different geometries( If you were to do a disk erercise with and waster method, then A(x) is always a damn circle)
    The shell method is sort of like the waster method, but all you are doing is rotating a figure accross a given axis.
    My recommendation is to read that section 5 times, and try to understand it intuitively. My advice cannot do a damn thing for you, but it helps me to reflect more deeply.
    Last edited: Dec 28, 2005
  8. Dec 28, 2005 #7


    User Avatar
    Homework Helper
    Gold Member

    http://mathworld.wolfram.com/PappussCentroidTheorem.html" [Broken]
    The theorem is very interesting, is it not?
    Last edited by a moderator: May 2, 2017
  9. Jan 2, 2006 #8

    Thanks Siddharth, Tide, Marlon, and Kant. All u guys have a Happy New Year.
    Last edited by a moderator: May 2, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook