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!

Jet on a rigid link question

  1. Sep 7, 2013 #1
    I have a mass (m) at the end of a rigid link of length r, pivoted at the red circle (below).

    m is acted on by a force (F) which is always normal to the surface shown (thrust from a jet say).

    My question is will this system reach a steady state, ie will it have constant angular velocity or will the angular acceleration just carry on increasing?

    Thx Nic
  2. jcsd
  3. Sep 7, 2013 #2


    User Avatar
    Science Advisor
    Gold Member

    Here's a thought: the gravitational field at the surface of the earth is nearly constant - so if you drop a rock does it continue to gain speed as it falls?

    Note that if air resistance is to be taken into account you there is a terminal velocity.
  4. Sep 7, 2013 #3


    User Avatar

    Staff: Mentor

    Angular acceleration and angular velocity are different things. If we ignore air resistance and friction at the pivot, the angular acceleration will be constant and the angular velocity will keep on increasing without limit until something breaks.

    If you consider air resistance, it is possible that the system will reach a steady state before something breaks. That force increases with speed, so as the speed increases will eventually be striping enough to counteract the applied force. (as UltrafastPED points out, this situation is analogous to the terminal velocity reached by a falling object in air).
  5. Sep 10, 2013 #4
    OK thanks both. This is what I thought (sorry about the velocity/acceleration mix up).

    Puzzling thing was, I ran this simulation in a well known CAD software & after an initial transitory increase in velocity it hit a steady state with no further acceleration!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook