# Motion of a damped harmonic oscillator due to air resistance

I did a video (30 fps) of the motion of of a mass suspended vertically by just one spring in one side. This spring is held by a rope connected to a fixed rod, as shown in the picture.

From the bottom to the top of the picture, we see, a bar of aluminium , another mass, a plastic ruler connected to the spring. The spring is connected to the rope on the other ending. Sorry for the bad resolution of the picture.

Then I used the $$Tracker$$ to plot the motion of the mass - plot of points - tracks points from 20 to 20 frames - and I got some results that I did not expected what puzzles me.

Could anyone explain me the motion of "equlibrium position" - why it goes up and down?

I'm not entirely sure of the details of your set-up, but the deviations shown on your figures seem to be in the millimeter range ($$0.1 \times 10^{-2}$$ m) which are quite small given the size of the equipment. It might be worth fixing the mass in place, then checking the measurements to see what kind of noise/uncertainty you have in the measurement system under the best conditions. This might help you localize and better understand the source of the fluctuations. It may turn out to be the noise characteristic of the measurement system itself.