Every animated film you have ever seen is a series of still pictures. At the cinema, film runs at 24 frames a second; a hand-drawn character might change only twelve times in that second. There is no motion anywhere in the chain. Your brain adds it.
The big idea: animation is the art of designing the gaps. How many pictures, how far apart, and how each one is shaped decide whether a drawing feels heavy or light, alive or robotic. The two demos below let you play with exactly those choices.
Your brain fills in the motion
You may have learned that we see movies because of "persistence of vision," an afterimage that lingers on the eye. Psychologists have long rejected that as the explanation for seeing motion. The eye isn't a camera with a frame rate. What happens is closer to a guess: when one shape vanishes and a similar shape appears nearby a moment later, the brain concludes that a single thing moved. In 1912 the psychologist Max Wertheimer studied this with flashing lights; the illusion is now called apparent motion (or beta movement). Try it:
Two dots take turns lighting up. Start slow, then shorten the gap until the two lights become one dot jumping across.
With long gaps you see two lights taking turns. Shorten the gap and, at some point, you see one dot moving, even though nothing moves.
Ones, twos and the cost of a second
Animators count in frames. Drawing a new picture for every one of the 24 frames is called animating "on ones." Holding each drawing for two frames, twelve drawings a second, is "on twos," and it is the workhorse of hand-drawn animation: fully animated films are often done on twos, switching to ones for fast action. Television animation often uses far fewer drawings still, and moves only the parts that must move (a mouth, a blinking eye). That is called limited animation, and it is a budget decision as much as an artistic one.
One bounce per second. Change how many drawings it gets, then switch the classic principles on and off. The outlines show where every drawing in one bounce sits.
Your device asks for reduced motion, so the ball waits for you: use "Next drawing" to flip through it one picture at a time.
At 12 drawings per second each drawing is held for 2 film frames. With slow in and slow out, the drawings bunch together near the top of the bounce, where a real ball slows down.
Notice two things. First, at 4 drawings a second the ball stutters: below a certain rate apparent motion breaks down. Second, spacing matters more than count. Switch off "slow in & out" and the outlines spread evenly; the ball moves at a constant speed and suddenly looks like a machine part. Real things accelerate and decelerate, and the eye knows it.
Timing is how many drawings. Spacing is how far apart they are. Between them, they are the whole of weight, speed and personality.
The twelve rules from Disney's studio
In 1981 two of Disney's veteran animators, Frank Thomas and Ollie Johnston, set out in their book The Illusion of Life twelve principles the studio had developed since the 1930s. They are still taught in animation schools and apply to computer animation as much as to pencils. A few of the most useful:
| Principle | What it does |
|---|---|
| Squash and stretch | Objects flatten on impact and stretch when moving fast, keeping the same volume; it gives weight and flexibility. Switch it on in the demo. |
| Slow in and slow out | More drawings near the start and end of a move, fewer in the middle. |
| Anticipation | A small move the other way before the main action: a crouch before a jump. |
| Follow-through | Parts keep moving after the body stops: hair, a coat, ears. |
| Arcs | Living things move along curves, not straight lines. |
| Timing | The number of drawings for an action sets its speed, and light things react faster than heavy ones. |
Many ways to make the pictures
- Hand-drawn (cel) animation. Drawings traced and painted onto clear sheets layered over painted backgrounds. Disney's first feature, Snow White and the Seven Dwarfs (1937), proved audiences would sit through a full-length cartoon.
- Cut-out and silhouette. The oldest surviving animated feature, Lotte Reiniger's The Adventures of Prince Achmed (1926), was made from hand-cut paper silhouettes. An even earlier feature, Quirino Cristiani's El Apóstol (1917, Argentina), is lost.
- Stop motion. Real objects or clay figures moved a tiny bit between photographs, as in The Nightmare Before Christmas, Coraline and the Wallace & Gromit films.
- Rotoscoping. Tracing over live-action footage frame by frame, patented by Max Fleischer in 1917.
- Computer animation. Pixar's Toy Story (1995) was the first entirely computer-animated feature film. The computer calculates the in-between frames, but the animator still sets the key poses, timing and spacing: the same choices as the bouncing ball.
1. A film is animated "on twos." How many different drawings appear in one second at 24 frames per second?
- 24
- 12
- 2
Answer: 12. Each drawing is held for two frames, so 24 ÷ 2 = 12.
2. A ball's drawings are evenly spaced from the ground to the top. Why does it look wrong?
- There are too few drawings
- It moves at constant speed; real balls slow down near the top
- It needs more color
Answer: constant speed. Gravity slows the ball as it rises and speeds it up as it falls, so the drawings should bunch near the top. That's "slow in and slow out."
3. Why do we see motion in a series of still pictures?
- The eye keeps each image like a camera, so they blur together
- The brain infers that a shape which disappears and reappears nearby has moved
- Projectors move the images physically
Answer: the brain infers motion (apparent motion). "Persistence of vision" is the popular explanation, but psychologists have long considered it inadequate.
Animation is a sequence of still pictures that the brain stitches into motion. The art lies in timing (how many pictures) and spacing (how far apart), plus principles like squash and stretch, slow in and slow out, anticipation and follow-through that make drawings feel like they have weight and life. Every technique, from paper cut-outs to Pixar, makes the same choices.
Try this: make a 12-page flipbook in the corner of a notebook: a ball dropping and bouncing once. Draw it twice, once with evenly spaced positions and once with the drawings bunched near the top and squashed at the bottom. Flip both and feel the difference.
Go deeper:
📘 The Animator's Survival Kit by Richard Williams (the master class on timing and spacing, by the animation director of Who Framed Roger Rabbit)
📘 The Illusion of Life: Disney Animation by Frank Thomas and Ollie Johnston (the source of the twelve principles)
🌐 Related pieces in this library: How Movies Manipulate You · Perspective: How a Flat Surface Fakes Depth