The aluminum rod will produce a loud, clear tone that will last for a long time. Hold the rod at its center, strike one end with a hammer, and hold it vertically over the organ pipe. Or replace the tuning fork with an aluminum rod about 1/2 inch (1.25 cm) in diameter and at least 1 yard (1 m) long. Here’s another experiment you can do with this Snack: Try replacing the tuning fork with a speaker driven by an electronic oscillator (frequencies between 100 Hz and 700 Hz work well) or even with an audio recording of a tuning fork or oscillator. Search for the shortest length of the tube that produces resonance: This will be 1/4 wavelength. That means if you multiply the length of the tube by four, you will get the wavelength of the sound made by your tuning fork.īe aware, though, that for a particular tuning fork, there are other resonances of the tube at tube lengths of 3/4 wavelength, 5/4 wavelength, and so on. This means that one transit of the tube takes one-quarter of a tuning-fork cycle, or that one-quarter of a wavelength of sound will fit into the tube length. All sound waves travel at the same speed in air (about 350 meters per second), so the only way to get the sound wave back to the tuning fork sooner is to make the tube shorter.Ī pulse that starts at the tuning fork as a compression makes four complete transits of the tube (down as a compression, up as a compression, down as an expansion, up as an expansion) before it returns to the tuning fork as a compression. The sound wave has to bounce off the water and return sooner to be in sync with the tuning fork. The sound wave is only synchronized with the tuning fork at certain pipe lengths.įor higher frequencies, the tube needs to be shorter to resonate. When you change the effective length of the tube by moving it up and or down in the water, you change how long it takes for a sound wave to travel down and back up the tube. If the tuning fork creates a new compression at the same time an existing compression reaches the top of the tube, the two compressions combine and the sound gets louder. This process repeats over and over again. Air rushes into this expansion to create a compression. This produces a wave of expanded air that travels back down the tube, bounces off the water, and returns to the end of the tube. This expansion of the air doesn’t stop when it reaches the end of the tube, and the air molecules overshoot the open end of the tube. When the compression wave reaches the mouth of the tube, it expands outward into the air. The compression wave reflects off the surface of the water within the tube and then travels back up the tube (Note: in the diagram below, the water surface is referred to as the "bottom" of the tube). In a sort of domino effect, a pulse of compression (a sound wave) travels down into the tube. These molecules, in turn, squeeze the molecules next to them, and so on. Related DIY: This salt experiment with sound and vibration and this “secret bell” experiment from Scientific American.īonus: Watch Chladni Plate Sand Vibration Patterns and more videos about resonance, frequency, vibration, and sound.As the tuning fork bends outward in its vibration, it squeezes together the air molecules in its path (click to enlarge diagram below). Then watch this: Resonance, forced vibration, and a tuning forks demo. Read more about tuning forks at How Stuff Works. As the first tuning fork is struck, sympathetic resonance sets the second tuning fork and its neighboring ping pong ball(?) in motion. Here’s another version of the first experiment: Tuning Forks Resonance + Ping Pong Ball, this time with two tuning forks that have matching frequencies. Different animal species have varying hearing ranges. Sound waves below 20 Hz are known as infrasound. Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz elicit an auditory percept in humans. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. A quick definition of sound from Wikipedia: The second experiment, the amplification of sound as the tuning fork touches the table, starts at 3 minutes. Slow down the day’s pace and observe as each element of the experiment is introduced. This is a demonstration to prove that a vibrating body can capable of producing sound, a Science Sir video. You can’t see the tuning fork’s movement, but the styrofoam ball responds. A small styrofoam (or pith) ball on a thread is held next to a vibrating 512-C tuning fork.
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