Bounce with Expressions in Adobe After Effects

Step-by-Step Guide to Creating Bounce with Expression:

Step 1: Set Up Composition

1. Open Adobe After Effects.
2. Create a new composition with the following settings:
   • Resolution: 1920×1080 Pixels
   • Frame rate: 30 frames per second
   • Duration: 5 to 10 seconds (adjust as desired)

Step 2: Create a Circle Shape

1. Select the Ellipse tool from the Toolbar.
2. Set the Fill color to your preferred color and Stroke color to None.
3. Draw a circle shape on the screen and align it to the center.

Step 3: Add Keyframes for Scale Animation

1. Select the circle layer and press the “S” key to open the Scale properties.
2. Add a keyframe at the first frame with a scale value of 100%.
3. Move the time cursor to 2 seconds on the timeline.
4. Change the scale value to 100% again to create a slight pause in the animation.

Step 4: Add Bounce Expression to Scale

1. Copy the following expression:

amp = .1;
freq = 2.0;
decay = 5.0;
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}

1. Hold the ALT key on the keyboard and click the stopwatch icon next to the Scale property to add an expression.
2. Paste the copied expression into the expression panel.

Step 5: Adjust Expression Parameters

1. Since we don’t have Expression Control options, you can directly adjust the “decay” value in the expression to fine-tune the bounce effect. For example, change “decay = 4” to a different value to modify the behavior.

Step 6: Create Another Shape Layer

1. Hide the current shape layer (the one with the bounce animation).
2. Create a new shape layer.

Step 7: Add Position Keyframes

1. Select the new shape layer.
2. Press the “P” key to open the Position properties.
3. Add a keyframe at the first frame.

Step 8: Apply Bounce Expression to Position

1. Move about 10 frames forward on the timeline.
2. Drag the circle to change its position.
3. Copy the following position expression:

e = .5;
g = 20000;
nMax = 9;

n = 0;
if (numKeys > 0){
  n = nearestKey(time).index;
  if (key(n).time > time) n--;
}
if (n > 0){
  t = time - key(n).time;
  v = -velocityAtTime(key(n).time - .001)*e;
  vl = length(v);
  if (value instanceof Array){
    vu = (vl > 0) ? normalize(v) : [0,0,0];
  }else{
    vu = (v < 0) ? -1 : 1;
  }
  tCur = 0;
  segDur = 2*vl/g;
  tNext = segDur;
  nb = 1; // number of bounces
  while (tNext < t && nb <= nMax){
    vl *= e;
    segDur *= e;
    tCur = tNext;
    tNext += segDur;
    nb++
  }
  if(nb <= nMax){
    delta = t - tCur;
    value +  vu*delta*(vl - g*delta/2);
  }else{
    value
  }
}else
  value

1. Hold the ALT key on the keyboard and click the Position stopwatch icon to add an expression.
2. Paste the copied expression into the expression panel.

Step 9: Adjust Expression Parameters

1. Change the values in the expression to achieve the desired bounce effect. For example, you can experiment with different values for “freq,” “decay,” “gravity,” and “elasticity.”

Step 10: Preview and Export

Preview the animation by playing the timeline. Adjust the expressions and parameters as needed to achieve the desired bounce effect. Once you’re satisfied, you can export the composition to your preferred format.

This tutorial demonstrates how to create a bounce animation using expressions in Adobe After Effects. Feel free to customize the parameters and expressions to achieve various bouncing effects.