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Some gases are buoyant in air because they have a densities lower than that of air (about 1. This page is about the physical properties of gas as a state of matter In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different The density of air, ρ (Greek rho (air density is the mass per unit volume of Earth's atmosphere, and is a useful value in Aeronautics. 2 kg/m3, 1. 2 g/l). Lighter-than-air gases are used to fill craft called aerostats, which include free balloons, moored balloons, and airships, to make the whole craft, on average, lighter than air. Gallery Types of aerostats See also Aerodyne Aerostatics Airship Balloon "Ballooning" redirects here For the behavior of Spiders and other Arthropods see Ballooning (spider. A moored balloon is an inflated fabric structure often shaped like an Airship and usually filled with Helium that is restrained by a cable attached to the ground Terminology In some countries airships are also known as dirigibles from the French (fr ''diriger'' to direct plus -ible) meaning "directable" (Heavier-than-air aircraft include aeroplanes, gliders and helicopters. Overview Fixed-wing aircraft range from small training and recreational aircraft to Wide-body aircraft and military cargo aircraft. History Since 400 AD Chinese children have played with bamboo flying toys. )

Contents

Hot air

The density of a gas can be reduced by raising its temperature while leaving the pressure unchanged (Charles' Law). Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface In Thermodynamics and Physical chemistry, Charles's law is a gas law and specific instance of the Ideal gas law, which states that

Heated air is widely used as a lifting gas in hot-air balloons. The hot air balloon is the oldest successful human-carrying Flight technology (The gas in a hot-air balloon is not only heated air, but also includes the products of combustion from the balloon's burner. Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of )

The altitude of a hot air balloon is controlled by regulating lift. Altitude is the Elevation of a point or object from a known level or datum (plural data The hot air balloon is the oldest successful human-carrying Flight technology To increase lift, more heat is applied. To decrease lift slowly, the hot air is allowed to cool. To decrease lift quickly, hot air is vented and replaced with ambient air. Unlike balloons using low-molecular-mass gases (see below), hot air balloons require continual burning of fuel in order to remain aloft.

Low molecular mass gases

Because any given volume of any gas at a given temperature and pressure contains nearly the same number of molecules (Avogadro's law), any gas with a lower molecular mass than that of air will be lighter than air (at the same temperature and pressure). The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically These four properties that constitute an ideal gas can be easily remembered by the acronym RIPE which stands for - R andom Motion (molecules are in constant random motion Avogadro's law ( Avogadro's Hypothesis, or Avogadro's Principle) is a Gas law named after Amedeo Avogadro, who in 1811 hypothesized The molecular mass (abbreviated m of a substance, more commonly referred to as molecular weight and abbreviated as MW, is the Mass of one

A sealed balloon expands as it rises because air pressure decreases with increasing altitude. Altitude is the Elevation of a point or object from a known level or datum (plural data As buoyancy depends on the mass of the displaced gas (Archimedes' principle) and because air is less dense at higher altitudes, balloons which rise to high altitudes (such as weather balloons) have to be allowed to expand as they climb so as to support the same weight. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is A weather or sounding balloon is a Balloon (specifically a type of High altitude balloon) which carries instruments aloft to send back information In the Physical sciences weight is a Measurement of the gravitational Force acting on an object Weather balloons are made with strong elastic "envelopes" so that they do not burst as they expand.

Determining which gases are lighter than air is relatively straightforward. These gases must have a molecular mass less than 28. 97 (the average molecular mass of air) and exist as a gas at atmospheric temperatures and pressures.

Assuming one atom per molecule of gas, the heaviest possible atom that could meet these criteria is silicon, which has an atomic mass of 28. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass 1. However, silicon does not become a gas until it reaches a very high temperature. The same applies to the metals aluminum, magnesium, sodium, beryllium and lithium and the hydrides of these. WikipediaNaming Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 Lithium (ˈlɪθiəm is a Chemical element with the symbol Li and Atomic number 3 Carbon and boron have high boiling points, but methane and borane (the hydrides of carbon and boron) are lighter than air. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. In chemistry a borane is a chemical compound of Boron and Hydrogen.

The following is a list of all stable materials with a molecular mass under 28. 8 and a boiling point under 100°C. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid Although isotopes are not considered here, it should be remembered that for the replacement of hydrogen with deuterium (or even tritium) the large relative mass difference can alter some of the properties of that specific gas (eg rates of reaction). Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Therefore ND3 can be considered a gas very different from NH3.


Compound Formula Mass Comments
Nitrogen N2 28 Majority component of air (~78%)
Carbon monoxide CO 28 Toxic, flammable
Ethylene C2H4 28 Flammable, reactive
Diborane B2H6 27. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Flammability is the ease with which a substance will ignite causing Fire or Combustion. Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. Diborane is the Chemical compound with the formula B2H6 It is a colorless gas at room temperature with a repulsively sweet odor 6 Spontaneously flammable in air
Hydrogen cyanide HCN 27 Very toxic, flammable, and water soluble
Acetylene C2H2 26 Extremely flammable, reactive, and unstable when compressed
Neon Ne 20. Hydrogen cyanide is a Chemical compound with Chemical formula HCN Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 2 Noble gas
Hydrogen fluoride HF 20 Very toxic, very corrosive, and water soluble
Water H2O 18 Liquid at room temperature
Ammonia NH3 17 Somewhat toxic, slightly flammable, and water soluble
Methane CH4 16 Flammable
Helium He 4 Noble gas, expensive, very small size makes it prone to leakage, must be replenished often
Hydrogen H2 2 Very flammable, relatively inexpensive petroleum by-product, prone to leakage

HAHAMICE

The acronym HAHAMICE was used to help emergency responders remember the gasses which are lighter than air. History Noble gas is translated from the German noun de ''Edelgas'' first used in 1898 by Hugo Erdmann to indicate their extremely low level of reactivity Structure HF forms orthorhombic crystals consisting of zig-zag chains of HF molecules Toxicity is the degree to which a substance is able to damage an exposed organism Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Room temperature (also referred to as ambient temperature) is a common term to denote a certain Temperature within enclosed space at which humans are accustomed Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical History Noble gas is translated from the German noun de ''Edelgas'' first used in 1898 by Hugo Erdmann to indicate their extremely low level of reactivity Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 It stood for:

H - Hydrogen
A - Ammonia
H - Helium
A - Acetylene
M - Methane
I - Illuminating Gases (old term for natural gas)
C - Carbon Monoxide
E - Ethylene

This acronym left out several gases, and was later changed to 4H MEDIC ANNA:

H - Hydrogen
H - Helium
H - Hydrogen Cyanide
H - Hydrogen Fluoride
M - Methane
E - Ethylene
D - Diborane
I - Illuminating Gases
C - Carbon Monoxide
A - Acetylene
N - Neon
N - Nitrogen
A - Ammonia

As is noticeable, the acronyms do not include all gases lighter than air.

Many of these gases are not practical for use in balloons. The following combine poor lift with objectionable properties: carbon monoxide, hydrogen cyanide, hydrogen fluoride, diborane, ethylene and acetylene. Nitrogen has negligible lift. Neon is harmless and offers a modest degree of lift; however it costs roughly the same as helium, another noble gas with far superior lift. The four remaining gases (ammonia, methane, helium, and hydrogen) have been used as balloon gases.

Ammonia has sometimes been used to fill weather balloons. A weather or sounding balloon is a Balloon (specifically a type of High altitude balloon) which carries instruments aloft to send back information Due to its relatively high boiling point (compared to helium and hydrogen), ammonia could potentially be refrigerated and liquified aboard an airship to reduce lift and add ballast (and returned to a gas to add lift and reduce ballast).

Methane (the chief component of natural gas) is sometimes used as a lift gas when hydrogen and helium are not available. Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, It has the advantage of not leaking through balloon walls as rapidly as the small-moleculed hydrogen and helium. (Most lighter-than-air balloons are made of aluminized plastic that limits such leakage; hydrogen and helium leak rapidly through latex balloons. )

Hydrogen and helium

Hydrogen and helium are the most commonly used lift gases. Although helium is twice as heavy as (diatomic) hydrogen, they are both so much lighter than air that this difference is inconsequential. Both provide about 9. 8 N of lift (the force to lift 1 kg) per cubic meter of gas at room temperature and sea level pressure. The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface Helium is preferred because it is not combustible.

The relative lifting power of hydrogen and helium can be calculated using the theory of buoyancy as follows:

The density at sea-level and 0°C for air and each of the gases is:

Thus helium is almost twice as dense as hydrogen. However, buoyancy depends upon the difference of the densities (ρgas) - (ρair) rather than upon their ratios. Thus the difference in buoyancies is about 8%, as seen from the buoyancy equation:

The negative signs indicate that these gases tend to rise in air.

Thus hydrogen's additional buoyancy compared to helium is:

Many countries have banned the use of hydrogen as a lift gas for manned vehicles. The Hindenburg disaster is frequently cited as an example of the risks posed by hydrogen. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout The high cost of helium (compared to hydrogen) has led researchers to reinvestigate the safety issues of using hydrogen as a lift gas: with good engineering and good handling practices, the risks can be significantly reduced.

Water vapour

Although pure water is not a gas at room temperature and sea level pressure, water in the vapor phase mixes readily with dry air, as do any two gases, until the partial pressure of the water vapor reaches the saturation water vapor pressure at the current temperature. In a mixture of Ideal gases each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium Such moist air is lighter than dry air at the same temperature, because the molecular mass of water is lower than the average molecular mass of dry air. Most hot air balloons burn propane (or some other hydrocarbon) to provide heat; the combustion products have an average molecular mass of 29. 1; the "light" water vapor more or less compensates for the "heavy" carbon dioxide. Pure water vapor (steam) can be used to lift balloons; however, the question of condensation must be addressed somehow. Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase One route would be simply to tolerate the condensation - this supposes a rather large balloon. Alternatively, the balloon could provide insulation (for example have a double-walled structure) or the water vapour (if pure) could be maintained at least at the boiling point of water at the altitude of use (100°C at sea level; less higher) by a heating device. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer [There are intriguing possibilities in using a mixture of air and water vapor, at a temperature high enough for the water component to remain as vapor. ] Two research efforts are currently underway to build steam-filled balloons (see external links below), taking rather different approaches; both of them have succeeded in practical demonstration of steam as a lift gas.

Vacuum balloon

First proposed by Italian monk Franceso de Lana in 1670, the vacuum balloon would be the ultimate expression of displacement lift power. A frequent topic of blue sky thinking, the basic principle has remained the same: A container strong enough to preserve a vacuum that displaces sufficient air to lift the container and an additional load. However, to avoid crushing by atmospheric pressure would require materials far stronger than any now available (see unobtainium). Unobtainium is a humorous term that refers to any extremely rare costly or physically impossible material needed to fulfill a given design for a given application

See also

External links

Gallery Types of aerostats See also Aerodyne Aerostatics Airship Balloon Terminology In some countries airships are also known as dirigibles from the French (fr ''diriger'' to direct plus -ible) meaning "directable" "Ballooning" redirects here For the behavior of Spiders and other Arthropods see Ballooning (spider. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is The hot air balloon is the oldest successful human-carrying Flight technology
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