1. Not finding help here? Sign up for a free 30min 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!

Logarithmic decrement of a lightly damped oscillator

  1. Jun 27, 2011 #1
    1. The problem statement, all variables and given/known data
    The logarithmic decrement δ of a lightly damped oscillator is defined to be the natural logarithm of the ratio of successive maximum displacements (in the same direction) of a free damped oscillator. That is, δ = ln(An/An+1) where An is the maximum displacement of the n-th cycle. Derive the simple relationship between δ and Q.
    Find the spring constant k and damping constant b of a damped oscillator with mass m, frequency of oscillation f and logarithmic decrement δ.
    [Data: m = 4.0 kg; f = 0.9 Hz; δ = 0.029.]
    First, the spring constant k...

    Also, the damping constant b...


    2. Relevant equations

    [itex]\beta[/itex]=b/(2m)
    Q=[itex]\omegao/(2\beta)

    3. The attempt at a solution

    Given the diff eq:

    d2x/dt2+2[itex]\beta[/itex](dx/dt)+[itex]\omega[/itex]o2x=0

    I can solve this to find x(t), however I feel this is irrelevant because no initial condition or boundary conditions are given, so I am kinda lost here as to where go or to start at for that matter. Any suggestions are greatly appreciated, Thanks
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jun 28, 2011 #2

    ideasrule

    User Avatar
    Homework Helper

    The initial conditions don't matter. Can you write the exponential term of the equation of motion in terms of Q? This term controls the amplitude of the oscillator, so the ratio between successive amplitudes is just the ratio between successive exponential terms.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Similar Discussions: Logarithmic decrement of a lightly damped oscillator
  1. Damped Oscillation (Replies: 1)

  2. Damped oscillator (Replies: 8)

  3. Damping Oscillation (Replies: 1)

Loading...