How to Make Your Animations Bounce in After Effects (Inertia Expression Tutorial)
If you’re anything like me, you’ve probably animated something in After Effects, stepped back, and thought: “Looks fine… but it feels a bit stiff.”
In this quick tutorial, I walk through one of my favourite expressions — a simple line of code that adds inertia (or bounce) to your animations. Whether it’s position, scale, or rotation, this expression gives your motion that little bit of extra life — a subtle bounce that feels more natural and dynamic.
Why I Use This Expression All the Time
This is one of those little tricks that can instantly lift an animation. It’s subtle — but makes a huge difference. Clients won’t always know why something feels better, but they’ll feel it. And that’s often the edge you need.
This tutorial is part of my new YouTube series, LiamTuts, where I’m sharing short, to-the-point After Effects tutorials based on the tools and techniques I use in real-world client work across broadcast, corporate, and film.
I learned most of what I know from online tutorials back in the day (this was before YouTube really took off), so this is my way of giving back to the community — and hopefully helping a few up-and-coming motion designers get a bit further, a bit faster.
What You’ll Learn:
How to apply an inertia bounce expression to any property (position, scale, rotation)
The key variables to tweak (amplitude, frequency, decay)
Why anchor points matter when bouncing rotation
How to make things feel just right
Copy and Paste the Expression
amp = .1;
freq = 1.0;
decay = 4.0;
n = 0;
time_max = 4;
if (numKeys > 0){
n = nearestKey(time).index;
if (key(n).time > time){
n–;
}}
if (n == 0){ t = 0;
}else{
t = time – key(n).time;
}
if (n > 0 && t < time_max){
v = velocityAtTime(key(n).time – thisComp.frameDuration/10);
value + v*amp*Math.sin(freq*t*2*Math.PI)/Math.exp(decay*t);
}else{value}
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I’m uploading new tutorials whenever I get a spare window of time (twin dad life!). If you’re into motion design, VFX, or just want quick answers without the waffle — hit subscribe and follow the journey: