SHM - Damping question

Could someone please explain to me how do you know from where to start the initial displacement for damping graphs?

  • what are things that I should look out for in the question that would give me a hint.

Hi @muhc,

To help answer your question, I’ve pulled these past exam questions and answers from No Brain Too Small.

In this example, a person is on a swing and stops swinging at maximum displacement. So on our displacement - time graph we will be at maximum displacement at t=0. Since the question states amplitude is 3.10m, we would ensure that is the value on our displacement axis we would start from, then gradually decreases in amplitude over three periods.


Here we see the question has stated “from maximum negative displacement”, which is stated to be 0.150m, hence…


Here we are told “from when she is closest to the floor”, so we should realise this would be at maximum negative displacement. However, we are being asked to draw the velocity - time graph, so we need to know how displacement corresponds to velocity in SHM - if you aren’t sure, here is a graph from dataloggers my class created earlier this year:

You can see maximum negative displacement corresponds to zero velocity, but immediately afterwards the velocity increases into positive values. (I would strongly recommend knowing how the max, min, and zero values correspond for d-t, v-t, and a-t graphs for SHM - you can work them out logically if you understand a few key principles). So our v-t graph will start at zero, then increase:


You could now check your understanding by working through 2016 question 3.

I hope that helps.

1 Like

That makes a lot more sense thank you!