A Video Editing and Photography Blog

Being primarily an editor, things like expressions and command line code tend to intimidate me.  However, some expressions are so easy to use and already developed that I sometimes can’t resist but try them.  One of my co-workers was using this Inertia expression a lot recently so I thought I’d give it a shot.

It gives a rubbery aesthetic to your animation.

To apply the expression copy the expression below, option + click the stopwatch on the parameter you want to affect, and paste.

This expression allows you to over extend a keyframe value and it will naturally settle back into place.  I have used it for scale, position, and rotation.  It works great and is super simple.  The only values that you need to adjust to your liking are the amp, freq, and decay.

Inertia from Chadwick Shoults on Vimeo.

// Inertial Bounce (moves settle into place after bouncing around a little)
n = 0;
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){
v = velocityAtTime(key(n).time - thisComp.frameDuration/10);
amp = .05;
freq = 4.0;
decay = 2.0;
value + v*amp*Math.sin(freq*t*2*Math.PI)/Math.exp(decay*t);
}else{
value;
}