Thomas and Johnston put it plainly: a movement that starts slowly, speeds up in the middle and ends slowly is more natural and more convincing than a movement at constant speed. A car does not reach 60 in zero seconds, and it does not stop in zero centimeters. Our eyes know that before we do.
On paper, animators controlled this by spacing the drawings: close together near the poses, far apart in the middle. On a computer, the same idea became interpolation. You set two keyframes and the software fills in the frames between them, either in a straight line or following a Bézier curve. When I animated Fala, Vô!, most of the work after blocking the poses was exactly this: opening each curve and adjusting it by hand, one by one. The software does the math; the feeling is still yours.
Three curves solve almost everything
- Ease out, for things that arrive. Fast at the start, soft at the end. A card entering the frame should land, not crash.
- Ease in, for things that leave. Soft at the start, fast at the end. The exit takes off and gets out of the way.
- Ease in and out, for things that travel. A card moving from one place to another on screen starts soft and arrives soft.
The default curve of most software is a gentle ease in and out on everything. That is why so much motion looks the same. Choosing the curve per movement, and making it stronger than feels comfortable, is one of the quickest upgrades you can make.
How to read a speed graph
The value graph shows where something is. The speed graph shows how fast it is going, and it is the one that tells the truth. A good ease looks like a hill: low at the edges, one peak. A flat line is linear motion. Two peaks mean the movement hesitates in the middle, which is almost never what you want. If the peak leans to the left, the movement is front-loaded: it bursts and then glides. That is the signature of confident motion.
An exercise for this week
Pick one scene. Make its entrance curve twice as strong as the default and watch it three times. Then do the opposite. The first version will feel more expensive, and you will not want to go back.
Parts of this series come from Felipe Risallah's undergraduate thesis on the production of the 3D short film Fala, Vô! (Cinema and Audiovisual, UFES, 2023), and from The Illusion of Life: Disney Animation, by Frank Thomas and Ollie Johnston (1981).