By Prof. Liwayway Memije-Cruz a wave that is created by vibrating objects and propagated through a medium from one location to another refers to the physical sensation that stimulates our ears. In constructing sound, there must be a source for a sound. The source of a sound wave is vibrating object which produces the waves which are nothing but the sound waves. Longitudinal Wave. All sounds are produced by the vibrations of material objects When the Sound waves travels through the medium, the pressure is exerted at the particular points that creates two regions : 1. compression where pressure is more and the density of the medium is more and 2. rarefaction where the pressure is less and the density of the material is less. The travelling wave which is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing. The speed of sound is 343.2 m/s or 1,126 ft/s. a body that has the properties of inertia and elasticity set for vibration: pianos, violins, organ pipes, saxophone and vocal cords through air elastic material whether solid, liquid or gas. Human ear can hear the sound with a frequency between 20-20,000 hertz determined by the amount of energy that the sound wave carries with it. the average rate of flow of energy per unit area perpendicular to the direction of propagation measured by decibels (dB) involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. So if the media (or its properties) are changed, the speed of the wave is changed. Thus, waves passing from one medium to another will undergo refraction. Refraction of sound waves is most evident in situations in which the sound wave passes through a medium with gradually varying properties. Reflection of a wave is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. The Common examples include the reflection of light, sound and water waves. When Sound wave travelilng in a medium strikes the surface separating the two media, A part of incident wave is reflected back into initial medium obeying ordinary laws of reflection while the rest is partly absorbed and partly refracted or transmitted into second medium. When a Longitudinal sounds wave strikes a flat surface, sound is reflected in a coherent manner provided that the dimension of the reflective surface is large compared to the wavelength of the sound. The speed of sound in a medium depends on the medium’s modulus of elasticity and its density. The more elastic the medium, the faster is the speed of sound. = 33.5 m/s =0.6T where: = speed of sound T= temperature Medium m/s Ft/s Air 331.5 1,087 Carbon dioxide 258.0 846 Glass 5,500 18,050 Hydrogen 1.270 4,167 Iron 5.100 16,730 Water 1,450 4,757 The speed of sound varies depending on altitude, temperature and the medium through which it travels. For example, at sea level in a standard atmosphere, at a temperature of 59-degrees Fahrenheit (15 Celsius), sound travels 761 miles per hour (1,225 km/p/h). At a temperature of 32-degrees Fahrenheit (0 Celsius) the speed of sound drops to 742 mph (1,194 km/p/h). In altitudes above sea level the speed of sound is again different and will vary depending on prevailing factors. the height of anything above a given planetary reference plane, especially above sea level on earth. observed whenever the source of waves is moving with respect to an observer can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward shift in frequency for observers from whom the source is receding. It is important to note that the effect does not result because of an actual change in the frequency of the source. bodies that vibrate at a regular rate and have a definite frequency. bodies that do not vibrate at a regular rate. a signal or wave whose frequency is an integral (whole-number) multiple of the frequency of some reference signal or wave. also refer to the ratio of the frequency of such a signal or wave to the frequency of the reference signal or wave. a string stretched between two points vibrates when plucked and a wave travels along the string. The fundamental frequency of vibration of a stretched string is inversely proportional to its length when its tension and linear density are constant. Shorter strings produce notes of higher pitch. . • • • • •
