Torsional Pendulum, Logarithmic Decrement

[tone999]

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?

 

[rl.bhat]

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(x_o/x_n)
where n is the number of cycles, x_o is the initial amplitude and x_n is the amplitude after n cycles.