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The speed of sound: Why is it so different in air and water?
The speed of sound is the distance a sound wave travels per unit time in an elastic medium. Simply put, the speed of sound is the speed at which vibrations travel. In air at 20°C (68°F), the speed of sound is about 343 meters per second, while in water it is 1481 meters per second, almost 4.3 times faster. The difference between the two makes one wonder: Why does sound travel at such different speeds in different mediums?
In gases, sound exists mainly in the form of compression waves, while in solids, there are two types of waves: compression waves and shear waves.
First, the speed of sound depends on the properties of the medium it travels through, including its density, elastic modulus, and temperature. In air, the speed of sound is significantly affected by temperature. Generally speaking, the speed of sound increases as temperature increases. This is because when the temperature of the gas increases, the molecular activity increases, resulting in an increase in the speed of vibration transmission; while in water, the speed of sound is mainly affected by the density and elastic modulus of water. Water is about 800 times denser than air, which allows sound to travel through it more quickly.
Sound travels faster in solids because the molecules are more densely packed, providing a more efficient medium for transmitting vibrations.
Sound travels faster through different solid materials except water and air. For example, in steel, the speed of sound reaches 5,000 meters per second, while in diamond it is as high as 12,000 meters per second. This is because the structure of solids allows sound waves to be transmitted in a more efficient manner. In solids, sound exists in the form of compression waves and shear waves, and the existence of shear waves further enhances the propagation ability of sound.
In Earth's atmosphere, the speed of sound can vary from 295 to 355 meters per second, depending on altitude and temperature.
In fact, the speed of sound is not only a measure of the properties of matter, but also a phenomenon we often face in life. In fields such as aviation and navigation, the speed of sound is crucial to the design of aircraft and ships. When the speed of an object exceeds the speed of sound, we call it supersonic. This phenomenon has been extensively studied in many military and scientific applications. In the history of exploring this phenomenon, the study of sound by 17th century scientists like Newton and Laplace laid the foundation for our understanding today. For example, Newton calculated the speed of sound in air for the first time in "Mathematical Principles of Natural Philosophy". Although there were certain errors in his calculation results, this error was eventually corrected by later scientists.
The transmission of sound can be explained by a model: suppose there is a series of spheres connected together by springs, and sound waves are transmitted by compressing and expanding the springs.
When exploring these phenomena, we also need to consider other factors, such as the homogeneity of the medium and temperature variations. Sound propagation in a specific environment may be affected by many factors. For example, humid air increases the speed of sound because the density of water molecules is lower than that of oxygen and nitrogen, making sound propagation more efficient. The speed of sound is closely related to the properties of waves. We can observe that in different materials, compression waves and shear waves may arrive at the observer at different speeds even when measured at the same frequency. For example, in an earthquake, compression waves tend to arrive first, followed by shear waves. When we further study the propagation of sound, perhaps behind these concepts and phenomena, there is a deeper physical world opened up for us. In densely structured solids, the propagation of sound waves may represent a more hidden force; and in liquids or gases, does the existence of sound make us think about the complexity of propagation? In summary, the difference in the speed of sound in different media shows the wonder and complexity of nature. Have you ever thought about the physical meaning behind these phenomena?
