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Very simple spring constant questoin

  1. Apr 2, 2009 #1
    Hi,

    I've just been thinking about this too much and managed to confuse myself.

    Spring constant for a vertical spring: k=mg/[tex]\Delta[/tex]

    Is it the same for a horizontal spring on a frictionless surface?

    Thanks!
     
  2. jcsd
  3. Apr 2, 2009 #2
    No. Horizontally, it's just F = kx.
     
  4. Apr 2, 2009 #3
    Thanks

    So the "a" in F=ma in the horizontal case is just whatever acceleration the mass is undergoing, rather than g?
     
  5. Apr 2, 2009 #4
    Yes,you are right.
    During the horizontal motion

    F= ma = kx

    And during the vertical motion

    F = mg = kx

    If friction is taken into count that force also shall be taken into count.
     
  6. Apr 2, 2009 #5
    Newton's 2nd law says
    Sum of Forces = m*a
    not just F = m*a

    When written as F = ma, this tends to neglect that it is the sum of all forces on the particle (Newton's 2nd law is for a particle).

    Writing F = mg is prone to suggest errors. It is safer to write
    W = m*g
    as a reminder that it is the weight force specifically that is equal to mg.

    I am continually amazed at the number of people I see posting here who want to confuse the F's in F = ma and F = mg by setting them equal to each other! There is a dangerous lack of thinking going on.
     
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