Vibrations,+Waves,+and+Sound+2

//WAVES, VIBRATIONS, AND SOUNDS//  **// ﻿ //** Everyday your world is filled with a multitude of sounds. Sound can let you communicate with others or let others communicate with you. It can be a warning of danger or simply an enjoyable experience. Some sounds can be heard by dogs or other animals but cannot be heard by humans. The ability the hear is definitely an important sense, but people who are deaf are remarkable in the ways that they can compensate for their loss of hearing.
 * //  ﻿ ﻿ Waves,Vibrations, and Sound // **

** VIBRATION﻿﻿﻿S, SOUND, AND WAVES **

** What is sound and how does it travel? **
 * All of the sounds you heard on the previous page occurred because mechanical energy produced by your computer speaker was transferred to your ear through the movement of atomic particles. Sound is a pressure disturbance that moves through a medium in the form of mechanical waves. When a force is exerted on an atom, it moves from its rest or equilibrium position and exerts a force on the adjacent particles. These adjacent particles are moved from their rest position and this continues throughout the medium. This transfer of energy from one particle to the next is how sound travels through a medium. The words " mechanical wave " are used to describe the distribution of energy through a medium by the transfer of energy from one particle to the next. **
 * Waves of sound energy move outward in all directions from the source. Your vocal chords and the strings on a guitar are both sources which vibrate to produce sound waves. Without energy, there would be no sound. Let's take a closer look at sound waves. **

** What do waves consist of? **
 * Sound or pressure waves are made up of compressions and rarefactions. Compression happens when particles are forced, or pressed, together. Rarefaction is just the opposite, it occurs when particles are given extra space and allowed to expand. Remember that sound is a type of kinetic energy. As the particles are moved from their rest position, they exert a force of the adjacent particles and pass the kinetic energy. Thus sound energy travels outward from the source. **
 * Sound travels through air, water, or a block of steel; thus, all are mediums for sound. Without a medium there are no particles to carry the sound waves. The word "particle" suggests a tiny concentration of matter capable of transmitting energy. A particle could be an atom or molecule. In places like space, where there is no atmosphere, there are too few atomic particles to transfer the sound energy. **
 * Take an stero for an example . To produce sound, a thin surfaced cone, called a diaphragm, is caused to vibrate using electromagnetic energy. When the diaphragm moves to the right, its energy pushes the air molecules on the right together, opening up space for the molecules on the left to move into. We call the molecules on the right compressed and the molecules on the left rarefied. When the diaphragm moves to the left, the opposite happens. Now, the molecules to the left become compressed and the molecules to the right are rarefied. These alternating compressions and rarefactions produce a wave. One compression and one rarefaction is called a wavelength . Different sounds have different wavelengths. **

** What do sound waves look like? **
 * We cannot see the energy in sound waves, but a sound wave can be modeled in two ways. One way is to create a graph of the diaphragm's position at different times. Think of a number line. We call the diaphragm's rest position zero. As it travels to the right, it moves to an increasingly positive position along the number line. As is travels to the left, its position becomes more and more negative. The graph of the diaphragm’s position as it vibrates looks like the sine graph, with its highest point when the diaphragm is the farthest right and its lowest point when it is farthest left. **
 * Another graph can be made using the amount of force on the molecules versus time. The force is greatest when the diaphragm is moving through its original position. This is similar to the way we feel the greatest force on a swing as we move through the center, where we started. As the diaphragm moves to the right, there is less and less force. At its rightmost position, it is exerting no force (due to pressure) and begins its trip the opposite way. Similarly, the diaphragm is exerting no force at its leftmost position. For our graph, we say the force is least when the diaphragm moves through its starting position heading the opposite way. When the force is exerting a pulling force, we assign negative values to it. A graph of the force versus time also resembles the sine graph. **

** More about compression and rarefaction **
 * Compression and rarefaction are terms defining the molecules near the diaphragm. Compression is the point when the most force is being applied to a molecule and rarefaction is the point when the least force is applied. It is important to note that when a molecule to the right of the diaphragm is experiencing compression, a molecule to the diaphragm's left is experiencing rarefaction. For right side molecules, compression occurs when the diaphragm is in its original position, moving towards the right. This is where the molecule experiences the most force. Rarefaction happens when the diaphragm is once again in the center, this time moving towards the left. At this point, the molecule is experiencing the least force. **

** Different types of waves ** **Longitude**
 * As vibrations go back and forth, the sound waves produced move the same direction (left and right). Waves that travel in the same direction as the particle movement are called longitudinal waves. Longitudinal sound waves are the easiest to produce and have the highest speed. However, it is possible to produce other types. Waves which move perpendicular to the direction particle movement are called shear waves or transverse waves. Shear waves travel at slower speeds than longitudinal waves, and can only be made in solids. Think of a stretched out slinky, you can create a longitudinal wave by quickly pushing and pulling one end of the slinky. This causes longitudinal waves for form and propagate to the other end. A shear wave can be created by taking one end of the slinky and moving it up and down. This generates a wave that moves up and down as it travels the length of the slinky. **
 * Another type of wave is the surface wave. Surface waves travel at the surface of a material with the particles move in elliptical orbits. They are slightly slower than shear waves and fairly difficult to make. A final type of sound wave is the plate wave. **



**Shear**



**Surface**



**Plate(Symmetric)**



**Plate(Asymmetric)**



** Temperature and the speed of sound **
 * Temperature is also a condition that affects the speed of sound. Heat, like sound, is a form of kinetic energy. Molecules at higher temperatures have more energy, thus they can vibrate faster. Since the molecules vibrate faster, sound waves can travel more quickly. The speed of sound in room temperature air is 346 meters per second. This is faster than 331 meters per second, which is the speed of sound in air at freezing temperatures. **
 * The formula to find the speed of sound in air is as follows: **

v = 331m/s + 0.6m/s/C * T = ** Vocabulary ** = The displacement from equilibrium. || The reciprocal of the frequency. || value during one period of an oscillation. || strain produced, within the elastic limit. || of gravity and acquired momentum. ||
 * v is the speed of sound and T is the temperature of the air. One thing to keep in mind is that this formula finds the average speed of sound for any given temperature. The speed of sound is also affected by other factors such as humidity and air pressure **
 * Periodic Motion || Any motion that recurs in identical forms at equal intervals of time. ||
 * Simple Harmonic Motion || Vibratory motion in a system in which the restoring force is proportional to
 * Period || The duration of one complete cycle of a wave or oscillation;
 * Amplitude || Absolute value of the maximum displacement from a zero
 * Hooke's Law || The principle that the stress imposed on a solid is directly proportional to the
 * Pendulum || A body so suspended from a fixed point as to move to and fro by the action
 * Resonance || The vibration produced in such a state. ||

**Hooke's Law: F= -kx** **Potential Energy in a Spring: PEsp= 1/2 kx^2**

**Example1: A spring stret**c**hes by 18 cm when a bag of potatoes weighting 56N is suspended from its end.** **Known: Unknown:** **x=18cm k=?**

**F=56N PEsp=?0** **a. Use F= -kx and solve for k.** **k= F/x** **= 56N/ 0.18m** **=310 N/m**

**b. PEsp= 1/2 kx^2** **= 1/2 (310N/m)(0.18m)^2** **= 5.0J**

**Period of a Pendulum:T= 2(3.14)the square root of l/g**

**Example2: A pendulum with a length of 36.9cm has a period of 1.22s. What is the acceleration due to gravity at the pendulum's location.** **Known: Unknown:** **l= 36.9cm g=?** **T= 1.22s** **Solve for the unknown:** **T= 2(3.14)the square root of l/g** **g= (2(3.14))^2l/ T^2** **= 4(3.14)^2(0.369m)/(1.22s)^2** **= 9.78 m/s^2**

**Speeds of Sound**
 * __ **Material** __ || __ **Speed of Sound** __ ||
 * Rubber ||  60 m/s  ||
 * Air at 40oC ||  355 m/s  ||
 * Air at 20 oC ||  343 m/s  ||
 * Lead ||  1210 m/s  ||
 * Gold ||  3240 m/s  ||
 * Glass ||  4540 m/s  ||
 * Copper ||  4600 m/s  ||
 * Aluminum ||  6320 m/s  ||

** Wave Interference ﻿﻿ ** ** When two or more sound waves from different sources are present at the same time, they interact with each other to produce a new wave. The new wave is the sum of all the different waves. Wave interaction is called interference. If the compressions and the rarefactions of the two waves line up, they strengthen each other and create a wave with a higher intensity. This type of interference is known as constructive. **

** When we are moving, or a source producing a sound is moving, we hear things differently. You may have noticed that a train whistle gets lower as it passes you. The whistle is not changing pitch, but you are hearing a change. This principle is known as the Doppler effect. The Doppler effect is named after the Austrian physicist, Christian Johann Doppler, who discovered it. **
 * THE DOPPLER EFFECT **


 * What did Christian Johann Doppler discover? **
 * Doppler claimed that if a sound is getting closer to you, either because its source is approaching you or because you are going towards the source, the sound will seem higher than it really is. If you are heading away from a source or it is going away from you, he believed the sound would seem lower than its actual pitch. To test his theory, scientists hired 15 trumpeters to play on a moving train. As the train passed by them, they heard a drop in pitch, just like Doppler predicted. **


 * Sound waves exist as variations of pressure in a medium such as air. They are created by the vibration of an object, which causes the air surrounding it to vibrate. The vibrating air then causes the human eardrum to vibrate, which the brain interprets as sound.**


 * ESSENTIALS QUETIONS FOR YOUR PERSONAL USE **
 * 1) What is the energy that makes the sound happen?
 * 2) What conclusion can you draw about the speed of sound relative to the speed of light?
 * 3) What happens to the speed of sound when the
 * 4) temperature changes?
 * 5) Does sound travel faster or slower as temperature increases?
 * 6) What happens when you change the material through which the sound travels?
 * 7) Through which material does sound move faster? Why do you think it is faster?
 * 8) What is the difference in sound between the overlap area and the single color area?
 * 9) What is the difference in sound in the white area?
 * 10) If the noise the object makes is not changing, why do you hear a change?

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