It's almost like it's part of my contract. When there is a new trailer for some cool movie, I pretty much have to blog about it. Of course in this case it's the new trailer for Rogue One: A Star Wars Story.

Now for the fun part—find some physics thing in the video that could be analyzed or explained. Go ahead and watch it again. What could you find? What about the motion of an exploding storm trooper? Nope, I already did that. I could make a comparison between blaster bolt speeds in the trailer and other movies. Yes, that would work but there aren't many blasters in the trailer.

You can see that it's not so trivial finding something to analyze, but I did it. Here I will look at the motion of the weapon part of the Death Star as it is being assembled. Let's do it.

In order to get a measure of the speed of this part of the Death Star, I will need two things. First, I need to use a video analysis program. The basic idea is to look at the pixel location of an object in each frame of the video and from this get position and time data. There are several methods to accomplish this video analysis, but I like the free and awesome Tracker Video Analysis program.

The second thing I will need is some type of scale in the video so that I can get a conversion between pixels and some real distance units. Fortunately, everyone pretty much agrees that the the original Death Star had a diameter of 120 km. With that, I can find that the diameter of the circular part of the weapon (the deflector dish looking thing) is about 35 km.

That's really all I need. I can now mark the location of the dish in each frame of the video to get the following position vs. time data. Oh, I should point out that I'm assuming the frame rate is in real time. Also, the motion of the dish isn't quite perpendicular to the camera view so that the actual velocity of the dish would be larger (we can look at this later).

This looks fairly linear. The slope of a position-time graph gives you the velocity in that dimension so we get a value of 1.07 km/s. Yeah, that's pretty fast for construction work. But maybe they are in a hurry.

Let's do one more graph. How about the speed of the Imperial-class Star Destroyers that are near the Death Star? I can use the same ideas to find their motion but I will need to rescale the video since these spacecraft are closer to the camera. Wookiepedia lists the length of the ship at 1.6 km, so I will use that. Here's what I get.

From the slope of this line, I get a Star Destroyer velocity of 0.514 km/s. That's odd. The Death Star dish is moving faster than the cruising speed of a Star Destroyer. This doesn't seem like a good way to assemble a super weapon.

Homework

There are still unanswered questions. Here are some things for you to consider.