Bounce Expression

amp = 0.1; // Amplitude (Bounce height)
freq = 2.0; // Frequency (Bounce speed)
decay = 5.0; // Decay (Bounce fading speed)
n = 0; // Keyframe index
time_max = 4; // Maximum duration for bounce (after keyframe)

if (numKeys > 0) { // If there are keyframes
n = nearestKey(time).index; // Get nearest keyframe index
if (key(n).time > time) { // If the nearest keyframe is in the future
n--; // Go to the previous keyframe
}
}

if (n == 0) {
t = 0; // No bounce before the first keyframe
} else {
t = time - key(n).time; // Time since the last keyframe
}

if (n > 0 && t < time_max) { // If there's a keyframe and the bounce is within time limit
v = velocityAtTime(key(n).time - thisComp.frameDuration/10); // Get the velocity at keyframe
value + v * amp * Math.sin(freq * t * 2 * Math.PI) / Math.exp(decay * t); // Apply the bounce
} else {
value; // No bounce after the time limit
}