Damping Practicals

Using Tracker to Discuss Damping

Great teamwork this week, with teachers, technicians and students all getting some great results using tracker.

We wanted to see if we could get some damping examples.

We took a pendulum that was just over a metre long and set it in motion over a blue tray. We filmed the pendulum and uploaded this into tracker. Part of a metre stick was used for calibration purposes.

Theo has analysed this to try to show that the amplitude remains constant, if there is no damping. The graph does seem to shift a little towards the positive direction and we are having some good ideas as to why, such as camera slide and swinging forward and back rather than side to side,  but it was probably due to the blurred film.

We then poured water into the tray and repeated the experiment pulling the pendulum back to the same point. Angus produced the tracker trace below. This is pretty blurred and distorted due to the refraction by the water.

Daniel had a clearer film to analyse and got a great plot of displacement with time to show how the amplitude decays with time.

If you can afford the top of the range camera, unlike the teacher, you can get a lovely plot, even if the pendulum appears to be hanging upside down!

You can clearly see that the amplitude decreases. Calculating the period, peaks arrive at the following times

 Time (s) 2.23 4.67 7.07 9.53 11.9 14.4 16.8 19.3

This gives a period of approx. 2.4-2.5 seconds.