Dot Physics

Yesterday, I uploaded a post from my old site about slowing down time to make videos look like they were on the moon. If you haven’t read that, the short story is that it doesn’t look right when speed Apollo videos up so that the acceleration is -9.8 m/s².

What started that whole thing was an even earlier post. Here is an example of using video analysis (Tracker Video Analysis) to measure the acceleration of a jumping astronaut on the moon. In this case, it is the famous “jump salute” from Apollo 16 astronaut John Young.

First, thanks John (or whoever videoed it). This is a good video for analysis. Modeling people can be difficult, especially when they are floppy. In this case John Young was essentially rigid. Plus, the camera did not zoom or pan. Too bad there was not a meter stick in the frame.

So, that is the first task. To scale the video. I first thought of using the height of the astronaut, but I could not find that data (plus he is wearing that space suit). Instead, I used the length of the PLSS (Primary Life Support System) the big back pack thing.

This site – http://www.myspacemuseum.com/plss.htm gives the length of the PLSS as 26.4 inches (0.67 meters). Now to the data:

Here is a plot of the vertical motion of the astronaut during the jump. I fit a quadratic function to the data shown in the graph. This gives a downward acceleration of 1.4 m/s² which would correlate to 1.4 N/kg gravitational field. This is very close the the official Wikipedia value of 1.6 N/kg. I think there are two problems with this video. First, I need a better quality video – this one as duplicate frames. Second, I probably need a better item to use to scale the video. Nonetheless, this does not look like an a jump in a studio on Earth.