The effect on drag of a change in the speed of sound is more complex, because the effect depends on bullet velocity relative to the speed of sound, as well as on altitude and atmospheric conditions. Opposite changes in these altitude or weather conditions tend to increase air density and, therefore, drag. When air density decreases, bullet drag decreases because the air is thinner. Air density tends to decrease if altitude increases, or barometric pressure drops below the sea level standard pressure value, or air temperature rises above the sea level standard temperature value, or a combination of high temperature and high humidity occurs. One way is by a change in air density, and the other is by a change in the speed of sound. To answer the first question, we need to understand that changes in altitude and atmospheric conditions affect bullet drag in two different ways. First, the ballistics tables provide us with trajectory data for these sea level standard atmospheric conditions, but what will happen to our bullet trajectories if we shoot at a location above sea level or with other atmospheric conditions? The second question is, how can the ballistics tables be used for higher altitudes and other atmospheric conditions? The standard barometric pressure and temperature are nominal, or average, values for the Aberdeen location. The values of ballistic coefficient in the table in Section 1.0 also correspond to these standard conditions, as does the drag function G 1. The values of air density and velocity of sound corresponding to these conditions are: (The symbol Hg denotes the chemical element mercury.) ![]() These standard conditions are:īarometric pressure: 750mm Hg-29.53 inches Hg Army Ballistic Research Laboratories at the Aberdeen Proving Ground in Maryland. For the ballistics tables in Sierra’s atmospheric conditions are the ones used for many years by the U.S. Because altitude and atmospheric conditions vary from location to location and from day to day, a standard altitude and standard atmospheric conditions have been adopted for the purpose of computing ballistics tables. It is possible for the pitch of the voice to change since gas dynamics ( i.e., Bernoulli effect) is partially responsible for the closing frequency of the vocal folds, but I haven't been able to find any data which demonstrates such a change.5.1 Effects of Altitude and Atmospheric Conditionsĭrag depends on the density of the air and on the speed of sound, and these in turn depend on altitude, temperature, barometric pressure, and relative humidity at the firing point. The cavity resonances which determine the vocal formants would be raised by the higher sound speed, so the timbre of the voice would be different. Note that if the vibration frequency of the vocal folds does not change, the actual pitch of the voice is not higher. The high speed of sound is responsible for the amusing "Donald Duck" voice which occurs when someone has breathed in helium from a balloon. This is consistent with the general relationship for sound speed in gases since the density of helium is so much less than that of air. The speed of sound in helium at 0☌ is about 972 m/s, compared to 331 m/s in air. Sound speeds in other gasesīreaking the sound barrier with an aircraft It is not dependent upon the sound amplitude, frequency or wavelength.Ĭalculation note: You may enter temperature to calculate sound speed, or enter sound speed to calculate the corresponding temperature. It is important to note that the sound speed in air is determined by the air itself. This sound speed does not apply to gases other than air, for example the helium from a balloon. ![]() At 200☌ this relationship gives 453 m/s while the more accurate formula gives 436 m/s. If you measured sound speed in your oven, you would find that this relationship doesn't fit. This calculation is usually accurate enough for dry air, but for great precision one must examine the more general relationship for sound speed in gases. ![]() The speed of sound is m/s = ft/s = mi/hr. The speed of sound in dry air is given approximately byįor temperatures reasonably close to room temperaature, where T C is the celsius temperature,
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