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!

Change in Grav PE with the change in origin.

  1. Feb 28, 2012 #1
    If a 1kg object is 1.5 m heigh. I find its PE to be 14.7 J. If it falls to the ground, the PE of 14.7 J goes to 0 as the object approaches the ground. Right?

    Now say the origin has been moved to 1.5 m where the object lies. Is the object at 0 J at the origin and approaching -14.7 J as it approaches the ground?

    Thanks
     
  2. jcsd
  3. Feb 28, 2012 #2

    gneill

    User Avatar

    Staff: Mentor

    Hi mrhingle, welcome to PF.

    Yes, changes in PE are relative to a chosen zero reference. If you place the zero reference for PE at an origin at a given height, then excursions below that height are associated with negative values for the PE.
     
  4. Feb 28, 2012 #3
    Would both cases be a negative change in PE?
     
  5. Feb 28, 2012 #4

    gneill

    User Avatar

    Staff: Mentor

    ΔPE = PEfinal - PEinitial

    If ΔPE is positive then the change is positive. If ΔPE is negative then the change is negative.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook