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ch 02.qxd
10/24/03
6:43 AM
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occupy a given volume. Conversely, when pressure on a given volume of air is decreased, the air expands and occupies a greater space. Thatis, the original column of air at a lower pressure contains a Standard Sea Leve! smaller mass of air. In other words, the density is 29.92 Pressure decreased. In fact, density is directly proportionalto & pressure. If the pressure is doubled, the density is doubled, and if the pressure is lowered, so is the density. This statement is true, only at a o constant temperature. « m EFFECT OF T M E A UE ON DENSITY E PRT R Atmospheric The effect of increasing the temperature of a Pressure substance is to decrease its density. Conversely, decreasing the temperature has the effect of increasing thedensity. Thus, the density of air varíes inversely as the absolute temperature varíes. This statement is true, only at a constant pressure. In the atmosphere, both temperature and pressure decreasewith aititude, and have conflicting effects upon density. However, the fairly rapid drop in pressure as aititude is increased usually has the Figure 2-1. Standard sea level pressure. dominating effect.Henee, density can be expected to mercury—but as its thickness is limited, the higher decrease with aititude. the aititude, the less air there is above. For this EFFECT OF HUMIDITY ON DENSITY reason,the weight of the atmosphere at 18,000 feet The preceding paragraphs have assumed that the air is only one-half what it is at sea level. [Figure 2-1] was perfectly dry. In reality, it is nevercompletely dry. The small amount of water vapor suspended in ATMOSPHERIC PRESSURE the atmosphere may be almost negligible under Though there are various kinds of pressure, this certain conditions, but inother conditions humidity discussion is mainly concerned with atmospheric may become an important factor in the performance pressure. It is one of the basic factors in weather of an airplane. Water...
10/24/03
6:43 AM
Page 2-2
o
2-2
occupy a given volume. Conversely, when pressure on a given volume of air is decreased, the air expands and occupies a greater space. Thatis, the original column of air at a lower pressure contains a Standard Sea Leve! smaller mass of air. In other words, the density is 29.92 Pressure decreased. In fact, density is directly proportionalto & pressure. If the pressure is doubled, the density is doubled, and if the pressure is lowered, so is the density. This statement is true, only at a o constant temperature. « m EFFECT OF T M E A UE ON DENSITY E PRT R Atmospheric The effect of increasing the temperature of a Pressure substance is to decrease its density. Conversely, decreasing the temperature has the effect of increasing thedensity. Thus, the density of air varíes inversely as the absolute temperature varíes. This statement is true, only at a constant pressure. In the atmosphere, both temperature and pressure decreasewith aititude, and have conflicting effects upon density. However, the fairly rapid drop in pressure as aititude is increased usually has the Figure 2-1. Standard sea level pressure. dominating effect.Henee, density can be expected to mercury—but as its thickness is limited, the higher decrease with aititude. the aititude, the less air there is above. For this EFFECT OF HUMIDITY ON DENSITY reason,the weight of the atmosphere at 18,000 feet The preceding paragraphs have assumed that the air is only one-half what it is at sea level. [Figure 2-1] was perfectly dry. In reality, it is nevercompletely dry. The small amount of water vapor suspended in ATMOSPHERIC PRESSURE the atmosphere may be almost negligible under Though there are various kinds of pressure, this certain conditions, but inother conditions humidity discussion is mainly concerned with atmospheric may become an important factor in the performance pressure. It is one of the basic factors in weather of an airplane. Water...
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