I do not know a lot about making motion pictures or the particular results concerned, however I can think about a scene from the 1970s through the creation of the primary Star Wars film. In one scene, they should present an escape pod touring away from a insurgent blockade runner with the runaway droids R2-D2 and C-3PO. Things are tight, so they should do one thing fast.
What to do? According to a mannequin maker in this video (and as described in this post), the Star Wars crew constructed the escape pod from a Kentucky Fried Chicken bucket after which dropped it from a top of 18 toes whereas filming it from above. They then added some small flecks of trash to offer that explosive separation look that you simply see within the NASA Apollo missions. As the pod fell down, it seemed that the spacecraft was accelerating away. Seems like a very low-cost and artistic resolution.
But is it actually what occurred? Ah ha! We do not must take this without any consideration, we are able to truly check this story. If I can measure the movement of the escape pod within the scene from Star Wars, I ought to be capable to a minimum of decide if the mannequin was accelerating. If it strikes at a fixed pace, they will need to have created the impact by another means.
Here is the plan. Find the place of the mannequin as a operate of time. An accelerating object would have a position-time graph within the form of a parabola. So, I simply want the place knowledge. If I had a view of the “falling” mannequin from the facet, I may simply get position-time knowledge utilizing video analysis by every body within the scene.
Alas, I haven’t got that view. The lack of the facet view makes this evaluation each difficult and fascinating. If it was simple, it would not be that a lot enjoyable. Also, why do not extra individuals say “alas”? It looks as if a nice phrase.
OK, I can nonetheless get the gap from the mannequin to the digital camera by trying on the angular dimension of the picture. The angular dimension is a measure of how large the article appears as a substitute of its precise dimension. If you want an instance, maintain out your thumb and place it in between your eye and somebody’s head. Your thumb appears larger than that particular person’s head however clearly you do not have a large thumb (I am assuming).
If an object is sufficiently far-off, the size of the article is roughly equal to the arc-length of a circle that passes by way of that object if centered on the viewer. Here, this diagram ought to assist.
This relationship between distance, angular dimension and size solely works if the angular dimension is measured in radians (in order that an angular dimension of 2π would match up with the circumference of a circle).
Here is what we’ll do. Take the scene with the transferring escape pod. Assume that it is a rooster bucket with a diameter of about zero.2 meters. Mark the placement of two factors on the escape bucket (I nonetheless cannot recover from the KFC factor) and discover the gap between these. Oh, I have to assume some angular area of view for the digital camera—I am simply going to choose 1 radian to make it easy. Once I discover the “distance” between these factors, that might give the angular dimension. Then utilizing the angular dimension and the precise dimension, I can discover the gap to the digital camera.
After that, I get the next plot of distance from the digital camera to the KFC mannequin.
Umm…that appears like a parabola to me. If I match an equation to that knowledge, I get an acceleration of 1.65 m/s2—and that is not what I count on. The acceleration of a free-falling object (on Earth) ought to be 9.eight m/s2. Does this imply the video is pretend? Of course it is pretend, it is a film. It’s not actual life. They in all probability simply slowed down the playback body fee to make it look cooler. If you alter the body fee from 24 frames per second to 58.5 fps, it ought to have the proper acceleration. Of course which may make it look bizarre for an escape pod. But I am fairly positive that is simply a falling KFC bucket made to appear to be a spaceship—similar to the person mentioned within the video.
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