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!

Flywheel Diameter

  1. Oct 9, 2006 #1


    User Avatar

    Hey all,

    I realize that when weight is moved from the center of a flywheel toward the outer edge (or a larger diameter wheel is used), the capacity for energy storage increases. But I have no idea how to calculate how much that increase actually is, or whether the increase remains constant (proportionately) between the two as RPMs increase.

    Anyone have a formula handy for this? Hopefully with enough footnotes for a "non-engineer" who doesn't know many standardized formula abbreviations...

    Thanks, moo
    moo (moo') adj. Of no practical importance; irrelevant, such as a moo point (i.e. a cow's opinion).
    Last edited: Oct 9, 2006
  2. jcsd
  3. Oct 9, 2006 #2


    User Avatar

    Staff: Mentor

  4. Oct 9, 2006 #3


    User Avatar
    Science Advisor
    Gold Member

    Sure, a common problem.

    For a solid disc:

    I = mk^2 = (mr^2) / 2 = (p*pi**b*r^4) / 2

    Where I is the moment of inertia of your wheel, m its mass, p the material's density, b the disc's thickness, r its radius, and k the radius of gyration.

    k = r / (sqrt 2)

    Now, energy stored:

    E = (Iw^2)/2

    Where w is the angular velocity of your wheel, (2*pi*N) where N is the number of revolutions per second.

    Sorry about the lack of fancy text, write it out on paper!

    For non-disc-like flywheels, you will easily be able to find I geometrically; if you struggle give us a shout or have a quick look in a mechanics book.

    You following?
  5. Oct 9, 2006 #4


    User Avatar

    Thanks guys, that should do the trick. :wink:

    moo (moo') adj. Of no practical importance; irrelevant, such as a moo point (i.e. a cow's opinion).
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Flywheel Diameter
  1. Flywheel torque (Replies: 24)