Uniform Motion (Unscripted)

Uniform Motion (Unscripted)

>>Okay. Uniform motion. Well, uniform motion’s
the simplest type of motion. Example shown here would be something like a heavy bowling
ball rolling across the floor, and what makes uniform motion very simple is because the
speed is constant, the spacing is constant, so we have between each of these key poses
the same distance or spacing. Now in uniform motion besides the speed being constant, we
also have that the object is travelling in a straight line. For right now we’ll mostly
concentrate on the spacing being the same spacing from frame to frame or from key to
key. Now if we want to we can determine how fast the object is actually going in terms
of a speed given the size of things in view and how far things move from frame to frame.
So let’s just look at a simple example of that. If we have this bowling ball and it
starts out in this first position, and two frames later, it’s over here, and two frames
later it’s over here. So that would mean this would be shooting on twos. From this we can
use this table, which is a translation between speed in terms of miles per hour compared
with what distance something would travel in one frame, and in this example the ball
seems to be travelling about 20 inches between drawings, and so that means since we’re shooting
on twos, it’s travelling about 10 inches each frame, and we don’t have 10 inches per frame
in the table, but it’s somewhere between 10 miles an hour and 20 miles an hour, so roughly
15 miles an hour. Well, let’s look at another example of using this idea. Let’s look at
Wile E. Coyote on rocket skates in this classic scene from “Beep Beep. ” [ Music ] [ Background noise ] Well, in that scene if we go frame by frame,
here’s Wile’s position on two different frames, and just roughly estimating what’s the size
of his head or his ears and looking at how far is he travelling based on objects in the
near background, it looks like he’s travelling somewhere between 12 to 15 inches per frame.
So from this table, he’s going roughly 20 miles an hour. A little bit of a correction
since that video is playing at 30 frames per second instead of 24 frames per second, so
it’s actually a little bit faster, but pretty much that’s the ballpark value. Now you might
have thought that Wile was travelling something like 60 or 80 miles an hour or some breakneck
speed, but in reality the animators didn’t have to have him going so fast in order to
give an impressive looking speed because since the camera’s tracking him directly and we’re
seeing objects whizzing by just next to him, that already looks fast enough, and, in fact,
had it been any faster then the objects going past him in profile would have been a complete
blur and probably somewhat uninteresting. So, now one last thing about uniform motion
is that if we’re not viewing the motion in profile, if we’re seeing objects moving away
from us or towards us, then, of course, we have to account for perspective and uniform
spacings are not visually uniform in perspective. So here we see a classic example of a rail
line going off to the distance and these telegraph poles, and even though we realize that the
telegraph poles are equally spaced, this visual spacing in our field of view is shorter than
the spacing between the poles that are closer to us. That’s just part of perspective. So
naturally, uniform motion may not appear uniform due to this distortion of scale when you have
objects moving away from the camera or towards the camera. So this example like a bowling
ball moving away from the camera, these spacings at first might not necessarily appear uniform
but when you check using some of the simple tricks of perspective like diagonal lines
intersect at the halfway point, so we can verify that these spacings for these drawings
are actually equally spaced once you account for perspective. Now, naturally this is more
of an issue for animators working in traditional hand drawn or for storyboard artists, but
for CG animators, the computer takes care of calculating the effect of perspective.
So in summary, uniform motion is a very simple type of motion. The object’s moving at constant
speed with constant direction, so moving in a straight line. Spacings are uniform in uniform
motion after you account for any effects due to perspective. The larger the spacings, the
higher the speed, and if you want to go to the trouble of actually calculating the speed
based on the spacings, then we saw a table that had that, and then finally the visual
sense of speed varies with camera position and tracking. We saw that in the example with
Wile E. Coyote. He seemed to be travelling exceptionally fast but that was mostly due
to the camera tracking him and watching him in profile. So, well, uniform motion is important,
but it’s a little bit boring, so in the next tutorials we’ll get to some more interesting
types of motion. See you then.

2 Replies to “Uniform Motion (Unscripted)”

  1. Very helpful tutorials and explanations! Though it would be simpler if you also add in a metric system so that we wouldn't have to use online conversion or do the unnecessary math throughout the series:) Cheers!

  2. Glad you like them! I did think about including conversions for international viewers and will try to include those in the next version. Right now I'm putting these together for a class I teach in the US. Need to finish version 1 of the videos for the class, which should be completed in another month. Stay tuned.

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