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Bell Shake & Ring Motion (Impact-Driven Oscillation Expression)

About This Expression

This expression simulates the motion of a bell being struck, rung, or vibrated at regular intervals. Instead of moving continuously like a sine wave, it creates a short burst of rapid oscillation, followed by a moment of complete stillness.

This behavior closely matches real-world physics:

  • An object is hit
  • It vibrates intensely for a brief moment
  • The motion naturally dies out
  • The object rests until the next impact

The result feels intentional, physical, and believable—perfect for ringing bells, notifications, alerts, and impact-driven motion.

How the Motion Works

  • Interval Timing
    The animation repeats every interval seconds using modulo time logic.
  • Shake Duration
    The shake only happens during shakeDur. Outside this window, the value returns to zero.
  • High-Frequency Oscillation
    A fast sine wave (freq) creates the ringing vibration.
  • Natural Decay
    The amplitude fades out smoothly using a decay multiplier, preventing harsh stops.

This combination creates a convincing “hit → ring → rest” cycle.

Expression

interval = 2;
shakeDur = 0.5;
amp = 25;
freq = 30;
loopTime = time % interval;
if (loopTime < shakeDur) {
 Math.sin(loopTime * freq) * amp * (1 - loopTime/shakeDur);
 } else {
 0;
}

How We Use This Expression

Step 1: Choose the Property to Animate

This expression works best on:

  • Rotation (most realistic for bells)
  • Position (for shake effects)
  • Anchor Point (for pivot-based motion)

Select the layer you want to animate.

Step 2: Apply the Expression

  1. Reveal the property (e.g., press R for Rotation)
  2. Hold Alt (Windows) / Option (Mac) and click the stopwatch
  3. Paste the expression
  4. Click outside the editor to apply

The layer will now shake briefly at regular intervals.

Step 3: Set the Ring Timing

Adjust this value:

interval = 2;

Examples:

  • 1 → rapid notification shake
  • 2–3 → natural bell ringing
  • 5+ → occasional alert or reminder

Step 4: Control the Shake Feel

Fine-tune the realism by adjusting:

  • shakeDur → how long the ringing lasts
  • amp → strength of the shake
  • freq → sharp vibration vs heavy swing

Small changes make a big difference.

Step 5: Use With Proper Pivot

For bells:

  1. Move the Anchor Point to the top of the bell
  2. Apply the expression to Rotation

This creates a natural swinging-and-ringing motion instead of a flat shake.

Step 6: Combine With Sound & Effects

This expression works beautifully when paired with:

  • Bell or notification sound effects
  • Motion blur
  • Subtle scale or glow pulses
  • UI highlight animations

The motion and sound sync naturally because the timing is math-based.

Best Use Cases in After Effects

  • Bell ringing animations
  • Notification & alert UI
  • App onboarding cues
  • Impact or hit reactions
  • Icon shake feedback

Why This Expression Feels So Real

The key is rest. Real objects don’t move forever—they react, decay, and stop. By separating motion into bursts instead of loops, this expression avoids the artificial “always moving” look.

You get:

  • Physically believable motion
  • Clean looping logic
  • Full timing control
  • Zero keyframes or plugins

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