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

Homework Help: Question on the bimetallic rod

  1. May 1, 2006 #1
    Question 1: A bimetallic rod is composed of brass and copper.
    a. If the rod is subjected to a compressive force, will the rod bend toward the brass or the copper? Why?
    b. Justify your answer mathematically if the compressive force is 5.00 X 104 N.

    Here is my answer but I am having trouble with a formula for part (b).

    a) The Rod Is Going To Bend Towards The Copper
    b) Assuming Both The Rods Is Of The Same Crossectional Area. Copper Is Weaker In Compression Than Brass
    Irrespective Of the Compressive Load with Reference from Data Hand Book
  2. jcsd
  3. May 1, 2006 #2


    User Avatar
    Homework Helper

    This is a question about the Young Modulus (YM), I believe. From some web references, the YM for copper is greater than that for brass (which is a copper/zinc alloy). This means that for a given load (stress value), the copper will deform less than the brass (copper will experience less strain than the brass).

    Hence, when you place the two rods side by side, the copper part will end up longer than the brass part after the deformation. This means that the rod will bend such that the copper part is on the outside (convex part) of the curved rod, while the brass part is on the inside (concave part).

    I don't get what sort of numerical justification they're looking for in the second part, since no dimensions, etc. were given for the rod. Moreover, once the rod starts to flex, it ceases to become elementary to work out the way the deformation will proceed since different parts of the rod will be oriented at different angles to the applied compressive force. Assuming ideal and uniform flexing, you can use calculus to work it out precisely, but I don't think the question wants you to go that far.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook