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!

Lump disk mass to a point

  1. Jun 9, 2010 #1
    hello

    imagine a disk rotating by an axis that passes through the center of the disk

    how can we find the analogue of a mass rotating by an axis?

    I mean, how can we lump the whole mass of the wheel to a point?

    how much will be the distance of this point from the axis?

    for example to rotate a disk with radius 10 and mass 100 you need the same force as to rotate a point of mass 100 and rotation radius = ??

    I suppose the radius will be some less than 10 (since not all parts of the disk are at this radius), but how much exactly?

    thanks

    PS: we need to do this in order to calculate other things, eg angular acceleration, etc
     
  2. jcsd
  3. Jun 10, 2010 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    hello mather! :smile:
    We can't lump it to a point (because it needs to have the same centre of mass as the disc, otherwise it will wobble :redface:), but we can lump it to a ring, with the same mass as the disc, and whose radius is the radius of gyration

    see http://en.wikipedia.org/wiki/Radius_of_gyration" [Broken] :wink:
     
    Last edited by a moderator: May 4, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook