Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating g force for flywheel

  1. Nov 3, 2015 #1
    I need to determine the RPM just that the flywheel (that has an offset shaft) will travel faster than gravity (g force). Meaning my offset shaft will be falling faster than a falling object per se.

    So flywheel has a diameter of 0.1524m.

    h=1/2g*t^2
    t=0.144s (assuming we did 1.5x(9.8m/s) with h=0.1524m)

    angular velocity = 3.14/t = 3.14/0.144s = 21.82 rad/s
    Therefore the RPM is 208 RPM (1 rad/s = 9.55 RPM)

    Is this the right approach? Thank you.
     
  2. jcsd
  3. Nov 3, 2015 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Where does that formula come from and what does it represent?
    Why pi/t?

    It is not the right approach.

    There is a simple formula for centrifugal/centripetal forces, you can directly use it.
     
  4. Nov 3, 2015 #3
    I am simulating a ball dropping at the top of a circle and the time it takes to reach the bottom, hence using pi. The ball is under the g force.


    But ive seen this
    http://www.calctool.org/CALC/phys/newtonian/centrifugal

    This calculates the centrifugal force but i need the vertical component to be greater than g (downward gravity force)
     
  5. Nov 3, 2015 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Ah, then I misunderstood your first post. I thought you were interested in the instantaneous acceleration.

    Okay, then your approach is right.
     
  6. Nov 3, 2015 #5
    So the offset shaft will fall (or in reality, rotate about the center) at 1.5gs if I have 208 RPM?

    The centrifugal approach from the link I posted has it higher, 600+ RPM
     
  7. Nov 3, 2015 #6

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    I checked the numbers. With your diameter, I get 0.176 seconds of free-fall time. That corresponds to 17.823/s or 170.2 rpm.

    Using those numbers, the tool gives 2.47 g acceleration. That looks reasonable. Don't forget to convert diameter to radius.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook