The Physics of Reddit’s Spinning Solar System Icon
If the dots on the loading screen were planets, is their motion realistic? And can we actually model it?
by RHETT ALLAIN
PHOTOGRAPH: GETTY IMAGES
WHILE WAITING FOR Reddit to load on my phone, I wondered if I could do some physics with the loading icon. Maybe you’ve seen it. It looks like a mini solar system with four planets (two inner planets and two outer planets). Let’s model it!
We should start with some data. I can do a screen capture of the loading screen and then use my favorite video analysis program (Tracker Video Analysis) to get position and time data. Of course, the screen shows distance in units of pixels and that’s not very useful. I don’t know the actual size of this “planetary system” (or whatever it is), so I will just set the scale size to 1 outer orbital diameter unit. This is the distance across the whole orbit of one of the outer “planets.”
In order to see if this figure moves in some type of realistic way, I need to look at the motion of the planets. One of the simplest things would be to look at the angular position as a function of time. What is the angular position? If you were to draw a line from the middle of the center sun to one of the orbiting planets (in a flat plane), the angle between this line and the x-axis would be its angular position. This is the same as if you were using polar coordinates instead of Cartesian coordinates. By using the angular position instead of x and y coordinates, I can still map out the motion, but I don’t have to worry about the orbital size. Then I can see if different orbital distances have different orbital speeds.