1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Springs In Series

  1. Oct 8, 2003 #1
    Two springs are in series. You know the constants for each individual spring. How do you find the spring constant for the spring system?

    |-OOOOO---o---OOOOOOOOOO-| --->F
    In the middle of the spring system (where the "o" is) the net force is zero and we have
    k1x1=k2x2 disregarding sign
    x3 =x2+x1
    but F=k1x1+k2x2

    Is this right?
  2. jcsd
  3. Oct 9, 2003 #2
    Looks OK.
    Now try to find a similar expression for N springs..:)
  4. Oct 9, 2003 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Looks to me like you have an extra factor of 2 in there. Springs in series add as Resistors in parallel. So

    1/KT = 1/K1+ 1/K2


    KT= (K1+K2)/(K1K2)

    Also Springs in parallel add as resistors in series.


    I do not have time to do the derivation now. Should be able to post it later to day. A key is that in the series case the force seen by each spring is equal, while in the parallel case the extensions are equal.
  5. Oct 9, 2003 #4
    Ah, I see my mistake. I have F=k1x1+k2x2 but F=k2x1=k1x1. I need to be more careful.
  6. Oct 9, 2003 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Last edited by a moderator: Apr 20, 2017
  7. Oct 9, 2003 #6
    Thank you, Integral. I have put your work into my physics notebook (hope you don't mind).
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook