## Tuesday, May 20, 2014

### Tracker: rebeccaoei student video slinky traveling down steps motion

Tracker: rebeccaoei student video slinky traveling down steps motion

 http://weelookang.blogspot.com/2014/05/tracker-rebeccaoei-student-video-slinky.html physics of slinky traveling down steps motion author of video: rebeccaoei

 http://weelookang.blogspot.com/2014/05/tracker-rebeccaoei-student-video-slinky.html physics of slinky traveling down steps motion author of video: rebeccaoei

## Mentoring

1. The angle of the camera isn’t exactly parallel to the “stairs” in my opinion. I have already filmed another video where the camera is parallel to the middle step - does this make it as accurate as possible?

it looks great to me, i would not retake unless you find the existing video lacking in details you need or want.

1. Is the resolution of the video too poor to track accurately? I felt that there was no need to use a high speed camera, but I am not sure if this will effect my results too greatly.

there is no need for high speed if you have already demonstrated that this video is clear enough for the purpose of your study
the results do not change, it can only get more precise :)

1. I only noticed after running the video in tracker that the ‘falling’ end (the end coming down from the first step) hits the second step before going onto the third step. This is reflected in a slight increase in the y velocity (more obvious for the yellow end tracked in blue dots, where the first two flips of that end hit the step, and the last doesn't.) Should I try to video another one where it does not have this problem, or acknowledge the problem my report?

i think the video is great the way it currently is, i do not see a need to re film since your data seems reasonable accurate and you can address the differences in the graphs you mentioned.

1. The acceleration for y never really reaches -9.81, is this because of the tension of the rest of the slinky pulling the end back up even as gravity acts on it?

i don’t see ay = -9.81 in your ay vs t graph,

i would explain the motion is the following details.

at t =0.63 s, ay = +8 because of the hitting of the red end of the slinky on the steps 2
from t = 0.64 to 1.4 s, the ay =0 because the red end is stationary
from t = 1.4 to 1.7, ay has a -peak greater than |9.81| probably the spring compression causes added acceleration.
at t 1.7, ay has a large +peak = 24.65 because it hit the step ( the unintended motion you mentioned?)
from t =1.9 to 1.935, it falls at less than |9.81|
at t = 2.002, red end slinky hit the desired step and experience ay = +8.52 probably due to the contact force from the step.

so depending on what you want to explain, you may want to zoom into more details on those parts

1. Is it better to track the point of the end of the slinky that is nearest to the camera, or the middle of the last coil as what I tried to do?

the best is film squarely to the motion which your video is pretty good enough, do you have evidence to suggest the video needs to re take?

1. Is there a way to display the graphs for the two ends together?

yes, in tracker 4.8 and higher, you can do a compare with

Thank you!
y

can i share your TRZ on my blog?
i normally will share if i can build a model but the slinky motion is too complex for me to model ( use equations to represent!)

thanks!