Sound Demonstrations

Sound is a form of energy that travels as vibrations through a medium such as air, water, or solids. This category explores how sound is produced, how it moves, and how it is detected. Understanding sound links physics to everyday experiences such as speech and music, and also to technologies that use sound waves.

Demonstration	Materials	Difficulty	Safety	Summary
Alarm Clock in Vacuum - Bell Jar	★★★	★★☆	★★★	A ringing bell inside a bell jar becomes quieter as air is removed with a vacuum pump, eventually falling silent when no air remains. When air is let back in, the sound returns.
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.
Chladni Plates	★★★	★★☆	★☆☆	When a flat metal plate is vibrated, sand sprinkled on its surface collects at the nodal lines where no motion occurs. This creates symmetrical patterns, known as Chladni figures, which reveal the modes of vibration of the plate.
Cornstarch Dancing on a Speaker	★★☆	★☆☆	★☆☆	A mixture of cornstarch and water, known as oobleck, is placed on top of a speaker. When sound waves vibrate the speaker cone, the non-Newtonian fluid forms strange, moving shapes, making sound waves visible.
Doppler Ball	★★★	★☆☆	★☆☆	A Doppler ball contains a speaker that emits a constant tone. When the ball is thrown or swung on a string, the pitch of the sound changes due to the Doppler Effect, demonstrating how relative motion alters perceived frequency.
Doppler Effect with Water Waves	★★☆	★★☆	★☆☆	The Doppler Effect can be modeled using water waves. When a source of ripples moves through still water, the wavefronts bunch up in front of the moving source and spread out behind, showing how relative motion affects wave frequency.
Harmonic Knives	★☆☆	★☆☆	★☆☆	This demonstration shows how a knife vibrates when struck and how holding it at different points changes the sound produced. By gripping the knife at a node, vibrations continue and produce a clear tone, while holding at an antinode dampens vibrations and creates a dull sound.
How Heat Sings	★★★	★★★	★★☆	When a PVC pipe is placed over a propane torch flame, the heated air resonates within the tube, producing a tone. The pitch depends on the length of the pipe, with longer tubes producing lower tones.
Measuring the Speed of Sound with a Drum	★★☆	★☆☆	★☆☆	One student beats a drum at a steady rate while others back away until the strike is seen at the same instant the previous beat is heard. Using the beat period and the measured distance at that point, students estimate the speed of sound.
Music Box on Bench	★☆☆	★☆☆	★☆☆	A small music box is played while held in the air, producing a faint sound. When pressed against a solid surface (like a bench), that surface vibrates, amplifying the sound and demonstrating forced vibration and resonance.
Musical Bottles	★☆☆	★☆☆	★☆☆	Blowing across the tops of bottles with varying water levels produces musical notes of different pitches. The pitch depends on the amount of air inside the bottle, with less air producing higher frequencies.
Rubens Tube	★★★	★★☆	★★☆	A Rubens tube is a long metal pipe with holes along its top, filled with propane and lit to produce flames. When sound waves are introduced through a speaker at one end, the flames reveal the standing wave pattern inside the tube, making sound waves visible as a dynamic flame display.
Singing Crystal Glass	★☆☆	★☆☆	★☆☆	When the rim of a crystal wine glass is rubbed with a wet finger, it vibrates at a resonant frequency and produces a musical tone. This experiment investigates how the shape of a wine glass and the amount of liquid it contains influence the pitch of the sound produced.
Slinky Waves	★☆☆	★☆☆	★☆☆	A stretched slinky can be used to model both longitudinal and transverse waves. By pushing or flicking one end of the slinky, students can see how wave energy travels through the coils.
Sound Localization	★★☆	★☆☆	★☆☆	Students investigate how two ears help the brain locate where a sound comes from by comparing the tiny time and loudness differences that reach each ear. Using a stethoscope headset connected to tubing, one partner taps at different positions while the listener identifies whether the sound is from the left or right.
Speed of Sound with a Resonance Tube	★★☆	★★☆	★☆☆	Use a water-filled resonance tube and tuning forks to find two resonance lengths for each frequency. From these lengths, determine the wavelength and calculate the speed of sound in air, with or without an end correction.
String Telephone	★☆☆	★☆☆	★☆☆	A string telephone demonstrates how sound vibrations can travel through a medium. When you speak into one cup, vibrations move through the string and are amplified in the second cup, allowing a friend to hear your voice.
Sympathetic Resonance with Tuning Forks	★★☆	★☆☆	★☆☆	When one tuning fork is struck and placed near another of the same frequency, the second fork begins to vibrate without being struck.
Tuning Fork in Water	★★☆	★☆☆	★☆☆	A vibrating tuning fork is struck and then placed in water. The vibrations disturb the water, producing visible ripples and sometimes splashes. This shows how sound is caused by vibrations and how energy can transfer between different media.
Tuning Fork on Bench	★★☆	★☆☆	★☆☆	A vibrating tuning fork produces a faint sound when held in the air. When placed on a solid bench, the sound becomes much louder because the vibrations are transferred to the bench, which acts as a resonator and amplifies the sound.
Tuning Forks Beats	★★☆	★★☆	★☆☆	Two sound sources with slightly different frequencies produce alternating loud and soft sounds called "beats." The beat frequency equals the difference between the two frequencies.
Virtual Oscilloscope	★☆☆	★☆☆	★☆☆	This demonstration introduces students to a virtual oscilloscope that can be run in a web browser or on a phone. Students can visualize sound waves from a microphone or signals in a simple circuit simulation, learning how amplitude and frequency appear on an oscilloscope screen.
Visualizing Sound Waves with an Oscilloscope	★★★	★★☆	★☆☆	An oscilloscope connected to a signal generator and speaker allows sound waves to be seen as patterns on a screen. By adjusting frequency and amplitude, students can explore how pitch and loudness correspond to wave characteristics.
Wireless Audio Transfer Using Laser Light	★★★	★★★	★★☆	Live audio is sent over a visible laser beam. A microphone signal modulates the laser; a light sensor (e.g., solar cell) converts the received light back to an electrical signal that is amplified and played on a speaker.

Materials
★☆☆ Easy to get from supermarket or hardware store
★★☆ Available in most school laboratories or specialist stores
★★★ Requires materials not commonly found in school laboratories

Difficulty
★☆☆ Can be easily done by most teenagers
★★☆ Available in most school laboratories or specialist stores
★★★ Requires a more experienced teacher

Safety
★☆☆ Minimal safety procedures required
★★☆ Some safety precautions required to perform safely
★★★ Only to be attempted with adequate safety procedures and trained staff