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!

Centre of mass of a solid hemisphere (feynman way)

  1. Sep 6, 2013 #1
    reference to Feyman lectures vol.1 topic 19.2 locating centre of mass

    Feyman gives us the law of pappus to find the centre of mass ,which he proves for semicircular disc and ring.

    But when i am trying to extend it to finding the centre of mass of a solid semi-circular solid hemisphere ,i seem to get a different answer from what i get from calculus which is 3R/8.

    My approach to problem is using law of pappus extensively:-

    1. I assume a solid semi-circular hemisphere into infinite number of semi-circular disc, find each disc's centre of mass using law of pappus.
    2. I get a ring with all centre of mass of respective discs.
    3. using that ring and law of pappus again i find the centre of mass of that ring.

    this value which i find doesn't correspond to 3R/8. is there something wrong in my approach
  2. jcsd
  3. Sep 6, 2013 #2


    User Avatar
    Science Advisor

    It would help if you showed the numerical details of your calculation.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook