Mason Blake
The speed of sound refers to the velocity of sound waves as they propagate through different mediums. It is typically measured in miles per hour (mph) and is influenced by factors such as temperature, medium, frequency, and pressure. The speed of sound is significant in various fields, including aviation and acoustics, and has been a subject of scientific inquiry since the 17th century, with scientists experimenting to determine its value in different conditions.
| Characteristics | Values |
|---|---|
| Definition | The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. |
| Mathematical Definition | The speed of sound is mathematically defined as the letter "c". |
| Equation | c = the speed of sound, C = coefficient of stiffness, g = density |
| Equation (in gases) | c = the speed of sound, y = adiabatic index, P = pressure, g = density |
| Speed of Sound in Air at 20°C | 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn) |
| Speed of Sound in Air at 0°C | 331 m/s (1,086 ft/s; 1,192 km/h; 740 mph; 643 kn) |
| Speed of Sound in Air at 0°C with no wind | 332 m/s |
| Speed of Sound in Solids | Sound travels fastest in solids. In tin, it is 7.5 times greater than in air, and in copper, it is about 12 times greater. |
| Speed of Sound in Liquids | Sound travels faster in liquids than in gases. |
| Speed of Sound at High Altitudes | 295 m/s (1,060 km/h; 660 mph) |
| Speed of Sound at High Temperatures | 355 m/s (1,280 km/h; 790 mph) |
| Speed of Sound in an Ideal Gas | Depends on temperature and composition. |
| Speed of Sound in a Fluid Medium | Used as a relative measure for the speed of an object moving through the medium. |
| Speed of Sound in Water | First measured by Jean-Daniel Colladon and Charles Sturm at Lake Geneva in 1826. |
| Factors Affecting Speed of Sound | Temperature, medium, frequency, pressure, wind direction, barometric pressure, humidity. |
| Aircraft Speeds in Relation to Speed of Sound | Subsonic, transonic, supersonic. |
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What You'll Learn
Speed of sound in mph at 20°C
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. In simpler terms, the speed of sound is how fast vibrations travel. The speed of sound is typically measured in metres per second (m/s), kilometres per hour (km/h), feet per second (ft/s), miles per hour (mph), or knots (kn).
The speed of sound varies depending on the medium through which the sound wave is travelling. For example, sound travels most slowly in gases, faster in liquids, and fastest in solids. In Earth's atmosphere, the speed of sound varies from about 295 m/s (660 mph) at high altitudes to about 355 m/s (790 mph) at high temperatures.
At 20°C, the speed of sound in air is about 343 m/s, 1,125 ft/s, 1,235 km/h, 767 mph, or 667 kn. This can also be rounded to 767.8 mph. The speed of sound in air can also be calculated using the following formula, where T = 20°C:
> c_air = 331.3 × √(1 + T/273.15)
At 20°C, the speed of sound in fresh water is about 1481 m/s.
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Speed of sound in mph at 0°C
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. In simpler terms, it is how fast vibrations travel. The speed of sound is dependent on the temperature and the medium through which the sound wave is propagating. For example, sound travels most slowly in gases, faster in liquids, and the fastest in solids.
The speed of sound in dry air at sea level (14.7 psi) and 0°C (32°F) is about 331 m/s (1,086 ft/s; 1,192 km/h; 740 mph; 643 kn). Values ranging from 331.3 to 331.6 m/s may be found in reference literature. The speed of sound in an ideal gas depends only on its temperature and composition.
The speed of sound is also affected by the humidity of the air, although the influence is small and can be neglected. This is because oxygen and nitrogen molecules of the air are replaced by lighter molecules of water, causing a simple mixing effect.
The speed of sound increases as the air temperature increases. For example, at 20°C (68°F), the speed of sound in air is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn).
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How temperature affects speed of sound
The speed of sound is the distance it travels per unit of time. It is measured at around 767 miles per hour (mph) or 1,235 kilometres per hour (km/h) at sea level and 20 degrees Celsius. The speed of sound is affected by various factors, including temperature, humidity, air pressure, wind direction, and the medium through which the sound waves travel.
Temperature has a significant impact on the speed of sound. As a rule of thumb, sound travels faster in warmer air than in cooler air. This relationship can be expressed by the formula, v=331+0.6T, where v is the speed of sound in meters per second (m/s) and T is the temperature in degrees Celsius. Thus, an increase in temperature corresponds to an increase in the speed of sound.
This phenomenon can be understood by examining the behaviour of gas molecules in relation to temperature. In gases, an increase in temperature leads to an increase in the speed of gas molecules. As sound waves rely on these molecules to travel from their source to our ears, the faster-moving molecules in warmer air facilitate the quicker transmission of sound. Conversely, in colder air, the slower-moving molecules hinder the propagation of sound, resulting in a lower speed of sound.
It is important to note that while temperature significantly influences the speed of sound, it does not affect the clarity or distinctness of sound. The perception of sound clarity is primarily determined by the amount of surrounding noise and the signal-to-noise ratio. For example, on a cold winter night, there is generally less noise due to reduced human and animal activity, resulting in a higher signal-to-noise ratio and improved sound clarity.
Additionally, temperature inversions, where the air near the ground is colder than the air above, can cause sound to refract downward and carry further. This phenomenon is more common during winter, contributing to the perception that sound travels better in colder temperatures. However, it is essential to distinguish between the speed of sound and its ability to propagate over longer distances, as they are influenced by different factors.
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How wind affects speed of sound
The speed of sound is around 767 miles per hour (mph) or 1,235 kilometres per hour (kph).
Wind can influence the speed of sound, depending on the direction of the wind in relation to the sound signal. If the wind is blowing in the same direction as the sound, the sound will be refracted towards the ground, and conditions will be favourable for sound propagation. Conversely, if the wind is blowing in the opposite direction to the sound, the sound wave will be refracted upwards, and losses of 20 decibels (dB) or more may occur.
For example, if the wind is blowing at 30 miles per hour (mph) or 13.4 metres per second (m/s), the speed of sound downwind will be 356.4 m/s, while the speed of sound upwind will be reduced to 329.6 m/s. Wind speed needs to be significantly higher to cause a noticeable increase or decrease in the speed of sound.
The speed of sound is also influenced by other factors, such as temperature and humidity. Temperature gradients can have a significant effect, particularly on still days. Lower temperatures result in higher air density, which reduces the speed of sound. Sound waves also travel faster through humid air than dry air.
Some sources suggest that the speed of sound is not affected by wind speed. They argue that the speed at which a disturbance propagates through a medium is not influenced by the velocity of the medium itself. However, the majority of sources state that wind does impact the speed of sound.
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How aircraft speed relates to speed of sound
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. In simpler terms, it is how fast vibrations travel. This speed is not constant and varies depending on the temperature, pressure, and composition of the medium through which the sound wave is propagating. For instance, at 20 °C (68 °F), the speed of sound in air is about 767 mph or 1,235 km/h, whereas at 0 °C (32 °F), the speed drops to about 740 mph or 1,192 km/h.
The speed of sound is a fundamental concept in aviation, influencing the design, performance, and operation of aircraft, especially at high speeds. Aircraft speeds are often compared to the speed of sound, and this comparison helps define performance characteristics and operational limitations. If an aircraft is moving slower than the speed of sound, it is said to be subsonic. When an aircraft is moving close to or slightly faster than the speed of sound, it is referred to as transonic, and at this stage, the aircraft encounters unique aerodynamic phenomena, including shock waves and significant increases in drag, known as the transonic effect. Managing these effects is crucial for aircraft designed for supersonic flight, which is when an aircraft moves faster than the speed of sound. Aircraft like the Concorde, which could cruise above Mach 2, and the Lockheed SR-71 Blackbird, which achieved sustained Mach 3+ flight, are examples of supersonic aircraft.
The Mach number is a term used to express the aircraft's speed in relation to the speed of sound. It is calculated as a percentage of the speed of sound. For instance, if an aircraft is moving at 600 knots, its Mach number would be 0.9. Depending on the aircraft's shape, size, and the atmospheric conditions, shockwaves can form when the aircraft moves close to or faster than the speed of sound. These shockwaves can have both negative and positive impacts on the aircraft.
Understanding the speed of sound and its implications is crucial for the advancement of aviation technology, the design of aircraft, and the optimisation of flight safety and efficiency. As aviation technology progresses, the pursuit of efficiently surpassing the speed of sound continues to drive innovation, shaping the future of both commercial and military aviation.
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Frequently asked questions
The speed of sound is about 767 mph at 20°C or 68°F. At 0°C or 32°F, it is about 740 mph.
The speed of sound increases with temperature. It also varies with altitude.
If an aircraft is moving slower than the speed of sound, it is subsonic. If it is moving close to or slightly faster than the speed of sound, it is transonic. If it is moving substantially faster than the speed of sound, it is supersonic.
