After Efffects swing (real world physics)

Make sure the "center" of the object, or where you want it to swing from, is the 0,0 (or whatever) anchor point.

ADD to rotation:

// 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 = 8;
freq = 2.0;
decay = 6.0;
value + (v/100)*amp*Math.sin(freq*t*2*Math.PI)/Math.exp(decay*t);
}else{
value;
}