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Torsional Pendulum, Logarithmic Decrement

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The amplitude of a torsional vibration decreases so that the amplitude on the 100th cycle is 13% of the the amplitude of the first cycle. Determine the level of damping in terms of the logarithmic decrement.

Is this simply ln(100/13)= 2.04

or ln(13/100)= -2.04?
 

Answers and Replies

  • #2
rl.bhat
Homework Helper
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The amplitude of a torsional vibration decreases so that the amplitude on the 100th cycle is 13% of the the amplitude of the first cycle. Determine the level of damping in terms of the logarithmic decrement.

Is this simply ln(100/13)= 2.04

or ln(13/100)= -2.04?
Level of damping δ = 1/n*ln(xo/xn)
where n is the number of cycles, xo is the initial amplitude and xn is the amplitude after n cycles.
 

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