![]() ![]() Each normal mode has a characteristic frequency and motion. For each body, there exist some natural ways in which it can vibrate. The exact vibration state is determined by how much of each normal mode of the body the initial impulse "awakens". Macroscopically, we see this as propagation of sound through the material. When struck, the atoms/molecules are set abuzz gyrating slightly about their equilibrium positions. Things which are nearly but not perfectly rigid are capable of vibrating. This is characterized by the moduli of elasticity of these bodies. A very nearly rigid body or elastic is the one which can be slightly deformed under applied stress(~force). An absolutely rigid body comprises of constituent atoms/molecules that absolutely don't budge from their initial positions. Here are some generic images illustrate the point: Its the pressure variation which travels away from the fork towards the listener. These generates local pressure variations which are what we call rarefactions and compressions. So the rapid movement compresses and "stretches" the nearby air volume. Once the prong starts vibrating at a fixed frequency, it moves rapidly towards and away from its nearby air molecules. In fact the prong would vibrate in pretty much the same way in vacuum too. You are right in thinking that the second prong, the one not struck, is not set in motion by the interveining air. Infact you don't even need the second prong(buzz of fly wings for example). Your emphasis is on explaining compression and rarefaction-for this how the tuning fork reaches its equilibrium vibrational motion isn't important. The exact mechanics of how the tuning fork vibrates is complicated*-however once set vibrating, the equilibrium motion is easy to understand-the to and fro movement of tuning fork prongs. ![]() I would really appreciate any diagrams to help my understanding too if possible however my ability in physics runs out after this thought! My second thought is that perhaps the vibrations are induced by the wave moving up and down the stem and not the air particles. So how do the tines end up moving together and apart (out of phase)? My assumption is that this would increase the pressure in-between the tines and move the second tine outwards but this would mean the tines are moving in phase. When the first tine is struck against an object (table) it would move towards the second tine. I understand the vibrational motion of the tines once the tuning fork has been struck however I'm confused with how it starts. My example of choice is to explain compression and rarefaction using a tuning fork example (seeing as this is a simple device that musicians will be familiar with). Keep reading to find out whether a tuning fork can make your teeth explode.I'm currently writing a book on music theory and I'd like to include some background information on the physics of sound waves. Due to cost considerations, however, most modern tuning forks are made out of stainless steel. Really soft metals like tin, gold and lead, meanwhile, won't make any noise at all. Soft metals like brass have a low, dull pitch. Dense metals like copper and steel vibrate with a crisp, high pitch. You can also adjust the pitch of a tuning fork by making it out of different materials. If someone ever finds a hammer big enough to hit it, the sound would most likely be too low to be heard by human ears. The largest tuning fork in the world, by the way, is a 45-foot (13.7-meter) sculpture in Berkeley, Calif. A loose string, on the other hand, takes longer to shudder back and forth, resulting in a lower tone. Without much room to wobble, a tight string vibrates quickly. ![]() It's the same principle as strings on a guitar. The smaller a tine, the less distance it has to move, and the faster it will be able to vibrate. To mimic the lowest key, on the other hand, it would only need to vibrate at 28 Hz.īut how do you adjust the speed at which a tuning fork vibrates? Well, first, you could adjust the length of your tuning fork. For instance, for a tuning fork to mimic the top key on a piano, it needs to vibrate at 4,000 Hz. The faster a tuning fork's frequency, the higher the pitch of the note it plays. ![]() The result is a steady collection of rarefactions and compressions that, together, form a sound wave. When the tines snap back toward each other, they suck surrounding air molecules apart, forming small, low-pressure areas known as rarefactions. When a tuning fork's tines are moving away from one another, it pushes surrounding air molecules together, forming small, high-pressure areas known as compressions. The way a tuning fork's vibrations interact with the surrounding air is what causes sound to form. ![]()
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