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Norman McLaren, the great 20th century pioneer of animation technique,

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once said, "Animation is not the art of drawings that move,

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but the art of movements that are drawn.

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What happens between each frame is more important

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than what exists on each frame."

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What did he mean?

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Well, for an object to appear in motion,

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it necessarily has to change in position over time.

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If time passes and no change in position occurs,

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the object will appear to be still.

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This relationship between the passage of time

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and the amount of change that occurs in that time

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is at the heart of every time-based art form,

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be it music, dance, or motion pictures.

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Manipulating the speed and amount of change

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between the frames is the secret alchemy

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that gives animation the ability to convey the illusion of life.

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In animation, there are two fundamental principles

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we use to do this:

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timing and spacing.

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To illustrate the relationship between them,

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we'll use a timeless example: the bouncing ball.

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One way to think about timing

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is that it's the speed, or tempo,

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at which an action takes place.

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We determine the speed of an action

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by how many pictures, or frames, it takes to happen.

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The more frames something takes to happen,

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the more time it spends on screen,

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so the slower the action will be.

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The fewer frames something takes to happen,

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the less screen time it takes,

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which gives us faster action.

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The timing is about more than just speed,

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it's also about rhythm.

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Like a drumbeat or melody only exists

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when a song is being played,

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the timing of an action

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only exists while it's happening.

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You can describe it in words,

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say, something will take 6 frames, 18 frames, or so on.

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But to really get a sense of it,

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you need to act it out

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or experience it as it would happen in, well, real time.

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Now, the timing of an action

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all depends on the context of the scene

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and what you're trying to communicate.

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What is doing the acting, and why?

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Let's take our example.

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What makes a ball bounce?

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The action we're talking about here

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is a result of interacting physical forces,

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a moving ball's tendency to stay in motion,

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or its force of momentum

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vs. the constant force of gravity

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bringing it back down Earth.

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The degree to which these invisible forces apply,

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and the reason why the ball behaves the way it does,

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all depends on the physical properties of the ball.

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A golf ball is small, hard and light.

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A rubber ball is small, soft and lighter.

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A beach ball is large, soft and light.

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And a bowling ball is large, hard and heavy.

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So, each ball behaves very differently,

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according to its properties.

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Let's get a sense of the visual rhythm of each.

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Each ball plays its own beat

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and tells us something about itself

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and the time it takes to travel across the screen.

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The visual rhythm of these hits is the timing.

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Okay, let's start animating our ball,

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bouncing up and down with a simple cycle of drawings.

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We'll draw a circle here,

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call it point A, our starting point.

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We'll have it hit the ground here, point B.

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Let's say it takes about a second

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to hit the ground and come back up again.

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This is our timing.

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Our spacing is where we position the circle

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in the frames between point A and point B.

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If we were to move our ball

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in evenly-spaced increments,

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we'd get something like this.

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It's not really telling us anything about itself.

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Is it a bouncing ball or a circle on an elevator?

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Let's look at our footage again

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and think about what's going on

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as each ball bounces.

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Following each impact with the ground,

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the ball's upward momentum

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is eventually overcome by gravity.

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This happens at the peak of each arc.

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As things change direction,

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the motion is slowest.

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We see here the successive positions of the ball

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are close together.

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The ball then speeds up as it falls,

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and is at its fastest

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when it's approaching and hitting the ground.

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We can see here each position is further apart.

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The change in position between frames

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is the spacing.

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The smaller the change,

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the slower the action will appear.

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The greater the change,

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the faster it will appear.

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For an action to decelerate,

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each change in position must be less than the change before it.

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Likewise, for an action to speed up, or accelerate,

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each successive change must be greater.

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Let's change the mechanical spacing

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of our animated bounce

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to reflect what we observed in the footage.

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Slow at the top, fast when it's hitting the ground.

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Simply by adjusting the spacing,

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we've succeeded in suggesting

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the forces of momentum and gravity at play

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and achieved a much more realistic motion.

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Same timing but different spacing

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gives us vastly different results.

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And in reality, as a ball bounces,

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the physics of gravity eventually defeat

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the tendency of the ball to stay in motion.

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You can see this here in the decreasing height

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of each successive bounce.

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However, again, this decrease varies

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according to the properties of the ball.

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Even though these circles are the same size here,

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they're each telling us a different story about themselves,

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purely in how they move.

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The relationship between these principles

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of timing and spacing

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can be applied in countless ways

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and used to animate all types of action:

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a yo-yo,

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a punch,

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a gentle tap,

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a push,

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a saw,

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the Sun traveling across the sky,

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a pendulum.

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Animation is a time-based art form.

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It may incorporate the aesthetic elements

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of other graphic arts,

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like illustration or painting,

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but what sets animation apart

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is that, here, what you see

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is less important that what you don't see.

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An object's superficial appearance

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only tells us so much about itself.

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It's only when it's in motion

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that we really understand its nature.