Elements of Physics, Waves, sound

The ocean pounding on the shore. The sound of music. Light emanating from the sun. And the transmission of a television program, but to these things have in common, they are all examples of energy being propagated by waves. Although we can not see many types of waves, nonetheless, they play a very important role in our physical world. We are going to look at the common characteristics and major differences of various waves and show how they are essential to the movement of energy on earth and through the universe. The waves that are crashing into this rocky headland were caused by the wind pushing against the water's surface. As each wave moves in from offshore, it is transporting the energy of that disturbance. This movement of energy is seen clearly when a stone is dropped into a pool of water. What happens is that the energy of the falling stone makes a disturbance in the water, and that disturbance creates the wave. As a wave radiates outwards, the water rises, and then falls. Eventually returning to equilibrium. What moves outwards with the wave is not the water, it is the energy of the disturbance. The energy is transported by two basic types of waves. Transverse and longitudinal. In a transverse wave, the disturbance is perpendicular to the direction of travel. While in a longitudinal wave, the disturbance is parallel to its direction of travel. But all waves have some common characteristics. The wavelength is the distance of one complete wave. This wave is measured from crest to crest, but it could be measured from any other points. Frequency is the number of wave cycles in a given unit of time. It is usually measured as the number of waves per second, and expressed as a hertz. Each Z. Amplitude is a maximum difference of the disturbance. Sometimes it is called the height of the wave. Velocity or the speed of the wave is the relationship between the wavelength and the frequency. It is found by multiplying the two together. The velocity of the wave is limited by the properties of the medium through which it travels. Wavelength frequency, amplitude, and velocity are common to all waves, but all waves are traveling disturbances that carry energy from place to place. Sound is a transfer of energy caused by any vibrating material, and is transmitted by longitudinal waves. Sometimes they are called compression waves. This slinky toy shows how it works. Notice how, as it is pushed out, some rings of the slinky bunch up and others are spread out. If we could see the longitudinal waves of sound, this is what they would look like. When a soundwave is created, the wave of energy moves outward from the source, pushing the air molecules back and forth parallel to the direction of the wave motion. The molecules next to the source of the sound are forced outward and bump into other molecules, passing the sound vibrations onto them. And so the energy of the vibrations radiates outward. When the wave arrives at the audience, the molecules vibrate the individual's eardrums and the listener interprets the vibrations as sound. The soundwaves have carried the energy of the music through the medium of the air. A medium can be air, water, or any solid material. It is essential for the transmission of sound because there must be molecules to vibrate and transfer the energy. We can't see the soundwaves in the air, but it can be easily demonstrated that sound creates waves. This tuning fork is vibrating at 440 cycles per second. When dipped into the water, a disturbance caused by the vibrations is clearly visible. The waves of energy have been transferred to the water. Our perception of sound is shaped by the nature of the wave. When allowed musical notice created, the amplitude or height of the wave is greater. The louder the noise, the higher the wave. The waves of this high pitched note have a high frequency. This means that it is producing far more waves per second than this low pitched note. The higher the pitch, the greater the frequency of waves. The human ear can hear a broad range of sounds from 20 hertz to about 20,000 hertz. In other words, we can hear frequencies from 20 waves per second to about 20,000 waves per second. Other animals can hear a much wider range of sound. Dogs, for example, can hear sounds up to 40,000 hertz. And bats up to 100,000 hertz. The speed of sound is dependent on the medium it travels through. But if there is no medium, there can be no sound. There is no sound in his face. There are no molecules to act as a medium to move the energy of the sound vibrations, and so space is soundless. So then how do astronauts hear? Their space capsules and space suits hold air, so they can breathe, and here. Sound always needs a medium to travel, and the speed varies somewhat depending on the temperature. At room temperature, the speed through the air is 343 m/s, or 1125 feet per second. At freezing point, sound travels at 332 m/s, or 1089 feet per second. But sound travels much faster in both liquids and solids. In the ocean, it travels at 1525 m/s, or 5000 feet per second. And in solids, much faster still. In Earth, sound travels at 3350 m/s, or 11,000 feet per second. The question is, why are there these differences in the speed of sound? The molecules in water are much closer together than in air, and in solid material they are packed even closer. In a dense medium, the sound vibrations do not have as far to travel. This is called the elasticity of the medium. The more elastic the medium, the faster the soundwaves will travel. Seismic waves from explosions and earthquakes send out very intense, longitudinal waves, with huge amplitude, the same as soundwaves, but they also transfer energy through transverse waves. These disturbances of energy can travel up to 7 times faster than the speed of sound in air. The waves can be of such magnitude that hillsides blow up and buildings collapse. Light has long been a fascination of scientists, but it travels so fast that it was very difficult to study. Isaac Newton, the brilliant English physicist, who lived in the 17th century, believed that light was made up of extremely small particles, but he could not explain how it traveled. Others believed that light was energy that traveled in waves, but they could not figure out how light waves could travel through space. By that time, quite a lot was known about sound, and it was felt that all energy needed a medium in which to travel. Scientists concluded that space had to be filled with some type of matter they called ether, which acted as the medium for light. In 1873, James clerk Maxwell, a British physicist, resolved most of these problems. Maxwell developed equations based on the earlier work of Michael Faraday, who had demonstrated the link between electric fields and magnetic fields. The oscillations or movements back and forth of electric charges generate electromagnetic waves of energy, which propagate as transverse waves. Maxwell's calculations of the velocity of these waves match the speed of light. And led him to predict that light is an electromagnetic wave. Since electric and magnetic fields can exist in both a material substance and a vacuum, these waves do not require a medium and can travel through air, water, or the vacuum of space. Once that was understood, physicists abandon the notion of ether. If we could see them, transverse waves would look something like the waves in this rope, or the ripples on the surface of a pond. This animation of an electromagnetic wave shows both the electrical and magnetic component of the wave. Note the two parts of the waves are at right angles to each other. Maxwell believed that electromagnetic waves were only energy. But it is now known that they are both waves of energy and particles called photons. This is called the wave particle duality. All electromagnetic waves travel through space at the speed of light. Our greatest source of electromagnetic waves is the sun. But it is also the energy and radio and television waves. Electric bikes, the leg emitted from fire, the atoms that make up matter and much more. Electromagnetic waves are everywhere in our universe. All waves can be distorted, deflected, or changed when they come in contact with a boundary. It is comparatively easy to see these effects with both water waves and soundwaves. But even electromagnetic waves are influenced by distortions. Reflected waves change direction when they bounce off a barrier. We have all heard sound echoes and understand that it occurs when soundwaves are reflected off a building or a cliff face. When sound travels through a medium like air and strikes another medium, like this canyon wall, some of the sound will reflect back to us as an echo. Sonar uses the same principle by transmitting soundwaves through the water and timing the echoes that come back. In order to create an image of the ocean floor. Dolphins use sonar echolocation to hunt for food. Reflection also works for other types of waves. These waves of water are being reflected off the rocks. Mirrors reflect light. Then we are able to see because of the reflection of electromagnetic waves. When light reflects off objects, those objects become visible to our eyes. This pencil appears to be broken at the water line. This is due to refraction. Electromagnetic waves travel faster in air than they do in water. And as a result, when they go from one medium to another, the image appears bent because the light ray deviates from its normal direction. Refraction is the basis of lens technology. It also occurs with soundwaves and all other waves. Diffraction is the term used when waves spread out around the edges of objects. This is why we can hear a round corners. Light waves can also be diffracted, and this phenomenon was put to use in the lens technology for beacons and lighthouses. Wow, that car horn had a high pitch as it approached, and a lower pitch as the car retreated down the street. That is called the Doppler effect. If the car was standing still, the soundwaves would travel at the same speed and the sound of the horn would have a constant pitch. But as the car comes towards us, each successive soundwave travels a shorter distance to reach our ears. The waves arrive at us more frequently and thus have a higher pitch. As the car travels away from us, each successive wave travels a longer distance to reach our ears and produces a lower pitch. Light rays also exhibit the Doppler effect. In the 1920s, an American astronomer named Edwin Hubble observed that the colors of the stars and other galaxies were similar to those in our own. But with one big exception, the colors were all shifted a little towards the red end of the color spectrum. Hubble realized that the reason for this is that the distance between other galaxies in our own had actually increased while the light from the stars had been traveling. In other words, the wavelengths of the light had been stretched over a longer distance, and therefore the wave frequency had been lowered. Just as it does for receding soundwaves. This discovery of the red shift is another example of the Doppler effect, and is the reason astronomers and physicists have concluded that the universe is expanding. Any object like this wine glass will vibrate and produce waves when it is disturbed. This is called its natural frequency. When one tuning fork is rung and brought close to another of the same frequency, the second fork begins to vibrate and harmony with the first one. It continues to ring even when the first fork is removed. This is called resonance, and always results in an increase in amplitude. When two waves meet while traveling in the same medium, wave interference occurs. If the displacement is in the same direction, both up or both down, it becomes constructive interference, and the amplitude increases temporarily as they pass each other. When soundwaves are nearly the same, they complement each other to produce a louder sound. This often happens when musical instruments are played together. Destructive interference occurs when waves overlap and the displacements are in the opposite direction. This can result either in silence or a softer sound than would be produced by the original waves. A standing wave can arise when two waves overlap. It occurs when waves of identical frequency traveling in opposite directions combine. In that situation, nodes are created where no movement of the medium occurs. In music, these unique frequencies are called harmonics and overtones, which make the sound more aesthetically pleasing. Architects and engineers apply the physics of sound in order to design buildings with good acoustics. And musicians learn how the sound is created in their instrument so they can maximize its effect. Constructive and destructive interference can have an effect on all waves. The most common interference in radio or television waves occurs when two signals overlap. Usually what happens is the frequencies are too close and they interfere with each other. The more physicists have learned about the nature of waves, the more they have come to understand the fundamental function waves play in the universe. Waves transport the energy of disturbances, true, or false. The number of wave cycles in a given unit of time is called the wave. The speed of the wave is called its. Soundwaves are longitudinal waves true or false. Longitudinal waves never need a medium to transport the energy. True? Or false? Sound travels faster in the air than in the ground. True. Or false. Visible light is transported by waves. The Doppler effect only applies to soundwaves. True. Or false. Echoes of sound and mirror images are examples of refracted waves. True or false. All waves can be distorted, deflected, or changed. True, or false.