Breaking Glass with Sound

A thin-walled wine glass can be shattered by sound if it is exposed to a tone at its natural resonant frequency. When the sound drives the glass strongly enough, vibrations build until the glass breaks.

1. Select a large wine glass with thin walls and a clear, ringing resonance when tapped.
2. Identify its resonant frequency by gently tapping and listening for the pitch.
3. Position the glass in front of a strong sound source such as a compression driver and amplifier.
4. Play a pure tone that matches the glass’s resonance, starting at low volume and increasing gradually.
5. Use a visual aid (such as a small piece of paper leaning against the rim) to confirm vibration.
6. Adjust frequency slightly lower than the tap-test pitch, since resonance shifts as vibration increases.
7. With sufficient power and resonance, the glass will shatter.

A MythBuster's Glass Shattering Montage - Jaime Vendera:

📄 How to breaking glass with sound - SalfordAcoustic: https://salfordacoustics.co.uk/how-to-breaking-glass-with-sound

• Instead of a loudspeaker, use a trained singer who can hold a steady pitch near the glass’s resonance, but still amplify electronically for safety and consistency.
• Try glasses of different shapes and thicknesses to compare resonance strength.
• Use high-speed video to capture the moment the glass deforms and breaks.
• Explore safe demonstrations of resonance using vibrating plates or tuning forks if breaking glass is impractical.

• Only attempt with proper equipment and training; not suitable as a casual classroom experiment.
• All nearby observers must wear safety goggles and hearing protection.
• Keep a safe distance; broken shards can scatter further than expected.
• Do not attempt by holding a glass near the mouth — dangerous if glass shatters unexpectedly.
• Secure the glass in place so that fragments do not travel toward the audience.

• Why does the glass break only at its resonant frequency? (Because resonance amplifies vibration amplitude until the glass structure fails.)
• Why is a thin-walled wine glass preferred? (It has lower damping and stronger resonance, making it easier to vibrate.)
• What real-world systems must engineers design to avoid resonance damage? (Bridges, skyscrapers, aircraft, and machinery must all avoid destructive resonance.)
• How does this connect to the concept of simple harmonic motion? (Resonance occurs when external driving frequency matches the system’s natural frequency, maximizing oscillation amplitude.)