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Arcs and smooth motion

From: 2D Character Animation

Video: Arcs and smooth motion

The concept of arcs is another animation principle you need to be aware of when animating. Now, arcs basically means that natural motion follows in arc. Anything that moves through nature typically moves along a curved arc of some sort. Very rarely do things move in straight lines through nature. Usually straight lines are caused by mechanical action rather than natural action. Now, what causes an arc is one of two things.

Arcs and smooth motion

The concept of arcs is another animation principle you need to be aware of when animating. Now, arcs basically means that natural motion follows in arc. Anything that moves through nature typically moves along a curved arc of some sort. Very rarely do things move in straight lines through nature. Usually straight lines are caused by mechanical action rather than natural action. Now, what causes an arc is one of two things.

The first is in-balance forces. So if we get a force coming from one direction and a force coming from another direction, the sum of those two forces will typically pull an object in a curved path. The second reason things move in an arc is because we can have pendulum motion which is that an object is pinned in one direction or another and it has to follow an arc because it's moving much like a pendulum. Let's go back to our standard bouncing ball, which is one example of something that moves in a straight line.

If the ball is falling straight down, it will tend to fall in a straight line. Now, remember that in this instance we only have one force acting upon this object, which is the force of gravity. So that's why it moves in a straight line. But typically in nature we don't have just gravity moving an object. Either the object has a direction that it's following, it has wind. There are all sorts of things that affect the motion of an object and very rarely does something move exactly straight down.

So in this case we have basically a two-dimensional motion. We have an object moving in more than one direction. We have more than one force acting upon it. So I've graphed this out, so we have the falling motion of the ball but we're adding in just a constant linear motion as if the ball was thrown in a direction. So we have two force vectors or two forces acting upon this ball. We have one that's pulling it straight down and one that's pulling it to the right.

So when we play this, you'll see that the ball actually follows in arc and if you want to see this a little bit clearly, I've ghosted it so you can see that this is actually moving in an arc. Now, the only reason that this moves in an arc is because we have multiple forces acting upon the object and the sum total of these forces moves it in an arc. So let's take a look at this in a character animation context. Again, if you have multiple forces acting upon an object, it'll move in an arc.

In this case, we have a character who is moving from one pose to another. So, as she moves from one pose to another, her legs relax, her body drops down because it's under the force of gravity, and then she kind of stands up again and regains her composure. But if you notice we actually have multiple forces acting upon this character. So, if we just look at the hips, we have the force of gravity pulling down, but we also have the force of the legs pushing it to the side, very similar to our bouncing ball.

In fact, I've graphed this out as well. So let's go ahead and follow this red dot. So basically she moves down and to the side and then back up and to the side. And the sum total of this is just a small arc. So again, even in character motion, things move in arcs. So let's go ahead and just play this at speed so you can see it. A very quick motion but it's still an arc. Now, the other reason that things move in arcs is because of pendulum motion. So let's take a look at that.

Now, what pendulum motion is, is that you have a weight that's pinned at the top, very much like the pendulum on a grandfather clock. In fact, let's go ahead just play this so you can very easily see how a pendulum works. So again, I'm going to go ahead and ghost this and when you see it ghosted, you can see that again this is moving in an arc. And it's pretty obvious because it's pinned, so it actually has to move in a circular arc, not even a parabolic or any other sort of arc.

It's basically a circular arc. Now, this works very similarly to the joints of a character. So, when we actually move that arm, you can see that it's actually moving along an arc. In fact I've gone ahead and added another red dot to this so we can actually see how this moves. So the hand is actually tracing an arc through space. So, as you interpolate or in between your animation you want to make sure that the objects that you're animating move along an arc. A lot of times you'll just move something from one place to another and the computer will in-between it and when the computer in-betweens it, it typically in-betweens in a straight line.

So you need to be conscious of arcs and make sure that you include them in your character's motion.

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This video is part of

Image for 2D Character Animation
2D Character Animation

73 video lessons · 22091 viewers

George Maestri
Author

 
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  1. 2m 18s
    1. Introduction
      1m 2s
    2. Using the exercise files
      1m 16s
  2. 48m 21s
    1. Designing characters
      3m 22s
    2. Tracing characters
      4m 32s
    3. Creating joints that work
      3m 53s
    4. Working with outlines
      4m 0s
    5. Accessorizing your characters
      2m 21s
    6. Creating parts for replacement animation
      1m 41s
    7. Rigging hierarchies in After Effects
      5m 33s
    8. Rigging replacement animation in After Effects
      5m 52s
    9. Rigging with the Puppet tool in After Effects
      3m 16s
    10. Rigging Flash characters
      5m 50s
    11. Rigging replacement animation in Flash
      4m 25s
    12. Rigging with the Bone tool in Flash
      3m 36s
  3. 55m 29s
    1. The first law of motion
      3m 3s
    2. The second law of motion
      3m 45s
    3. The third law of motion
      3m 19s
    4. Using slow in and slow out
      5m 34s
    5. Arcs and smooth motion
      5m 4s
    6. Understanding overlap and follow-through
      5m 16s
    7. Animating overlap and follow-through
      5m 46s
    8. Understanding squash and stretch
      3m 10s
    9. Animating squash and stretch
      4m 40s
    10. Squashing and stretching characters
      5m 16s
    11. Understanding weight
      3m 27s
    12. Understanding anticipation
      4m 54s
    13. Animating anticipation and weight
      2m 15s
  4. 45m 50s
    1. Internal vs. external forces
      4m 45s
    2. Bringing characters to life
      4m 57s
    3. Animating blinks
      4m 37s
    4. Animating changes in eye direction
      2m 43s
    5. Animating head turns
      8m 1s
    6. Creating a strong line of action
      4m 16s
    7. Creating strong silhouettes
      2m 19s
    8. Pose-to-pose animation: Blocking
      4m 32s
    9. Pose-to-pose animation: Animating
      4m 21s
    10. Pose-to-pose animation: Finalizing
      5m 19s
  5. 46m 53s
    1. A walk in four poses
      2m 27s
    2. Motion of the head and body
      1m 32s
    3. Walk cycles and backgrounds
      1m 40s
    4. Skeleton motion and walking
      4m 2s
    5. Animating a walk: Contact position
      3m 0s
    6. Animating a walk: The feet
      9m 10s
    7. Animating a walk: The body
      5m 19s
    8. Animating a walk: The legs
      8m 21s
    9. Animating a walk: The upper body and arms
      3m 46s
    10. Animating a walk: The head
      2m 50s
    11. Animating a walk: Squash and stretch
      4m 46s
  6. 26m 52s
    1. A run in four poses
      4m 10s
    2. Animating a run: First pose
      4m 39s
    3. Animating a run: Second pose
      3m 45s
    4. Animating a run: Third pose
      3m 27s
    5. Animating a run: Fourth pose
      5m 1s
    6. Animating a run: Upper body
      5m 50s
  7. 37m 6s
    1. The basics of dialogue animation
      4m 35s
    2. Reading tracks and assigning mouth shapes
      5m 33s
    3. Phonemes and lip-syncing
      8m 36s
    4. Animating dialogue: Animating the body
      6m 27s
    5. Animating dialogue: Assigning mouth shapes
      4m 10s
    6. Animating dialogue: Finalizing
      7m 45s
  8. 1h 27m
    1. Animating a scene
      2m 0s
    2. Setting up the scene in After Effects
      3m 2s
    3. Animating the feet in After Effects
      10m 40s
    4. Animating the legs in After Effects
      4m 21s
    5. Animating the upper body in After Effects
      9m 44s
    6. Animating the mouth and blinks in After Effects
      7m 5s
    7. Setting up the scene in Flash
      4m 6s
    8. Animating the feet in Flash
      9m 0s
    9. Animating the body in Flash
      5m 23s
    10. Animating the legs in Flash
      7m 24s
    11. Animating the hands in Flash
      11m 54s
    12. Animating the mouth in Flash
      12m 26s
  9. 33s
    1. Goodbye
      33s

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