Macroscopic Gas

1 macroscopic

1.1 pressure
1.2 temperature
1.3 specific volume
1.4 density

macroscopic

shuttle imagery of re-entry phase.

when observing gas, typical specify frame of reference or length scale. larger length scale corresponds macroscopic or global point of view of gas. region (referred volume) must sufficient in size contain large sampling of gas particles. resulting statistical analysis of sample size produces average behavior (i.e. velocity, temperature or pressure) of gas particles within region. in contrast, smaller length scale corresponds microscopic or particle point of view.

macroscopically, gas characteristics measured either in terms of gas particles (velocity, pressure, or temperature) or surroundings (volume). example, robert boyle studied pneumatic chemistry small portion of career. 1 of experiments related macroscopic properties of pressure , volume of gas. experiment used j-tube manometer looks test tube in shape of letter j. boyle trapped inert gas in closed end of test tube column of mercury, thereby making number of particles , temperature constant. observed when pressure increased in gas, adding more mercury column, trapped gas volume decreased (this known inverse relationship). furthermore, when boyle multiplied pressure , volume of each observation, product constant. relationship held every gas boyle observed leading law, (pv=k), named honor work in field.

there many mathematical tools available analyzing gas properties. gases subjected extreme conditions, these tools become bit more complex, euler equations inviscid flow navier–stokes equations account viscous effects. these equations adapted conditions of gas system in question. boyle s lab equipment allowed use of algebra obtain analytical results. results possible because studying gases in relatively low pressure situations behaved in ideal manner. these ideal relationships apply safety calculations variety of flight conditions on materials in use. high technology equipment in use today designed safely explore more exotic operating environments gases no longer behave in ideal manner. advanced math, including statistics , multivariable calculus, makes possible solution such complex dynamic situations space vehicle reentry. example analysis of space shuttle reentry pictured ensure material properties under loading condition appropriate. in flight regime, gas no longer behaving ideally.

pressure

the symbol used represent pressure in equations p or p si units of pascals.

when describing container of gas, term pressure (or absolute pressure) refers average force per unit area gas exerts on surface of container. within volume, easier visualize gas particles moving in straight lines until collide container (see diagram @ top of article). force imparted gas particle container during collision change in momentum of particle. during collision normal component of velocity changes. particle traveling parallel wall not change momentum. therefore, average force on surface must average change in linear momentum of these gas particle collisions.

pressure sum of normal components of force exerted particles impacting walls of container divided surface area of wall.

temperature


air balloon shrinks after submersion in liquid nitrogen

the symbol used represent temperature in equations t si units of kelvins.

the speed of gas particle proportional absolute temperature. volume of balloon in video shrinks when trapped gas particles slow down addition of extremely cold nitrogen. temperature of physical system related motions of particles (molecules , atoms) make [gas] system. in statistical mechanics, temperature measure of average kinetic energy stored in particle. methods of storing energy dictated degrees of freedom of particle (energy modes). kinetic energy added (endothermic process) gas particles way of collisions produces linear, rotational, , vibrational motion. in contrast, molecule in solid can increase vibrational modes addition of heat lattice crystal structure prevents both linear , rotational motions. these heated gas molecules have greater speed range varies due constant collisions other particles. speed range can described maxwell–boltzmann distribution. use of distribution implies ideal gases near thermodynamic equilibrium system of particles being considered.

specific volume

the symbol used represent specific volume in equations v si units of cubic meters per kilogram.

the symbol used represent volume in equations v si units of cubic meters.

when performing thermodynamic analysis, typical speak of intensive , extensive properties. properties depend on amount of gas (either mass or volume) called extensive properties, while properties not depend on amount of gas called intensive properties. specific volume example of intensive property because ratio of volume occupied unit of mass of gas identical throughout system @ equilibrium. 1000 atoms gas occupy same space other 1000 atoms given temperature , pressure. concept easier visualize solids such iron incompressible compared gases. since gas fills container in placed, volume extensive property.

density

the symbol used represent density in equations ρ (rho) si units of kilograms per cubic meter. term reciprocal of specific volume.

since gas molecules can move freely within container, mass characterized density. density amount of mass per unit volume of substance, or inverse of specific volume. gases, density can vary on wide range because particles free move closer when constrained pressure or volume. variation of density referred compressibility. pressure , temperature, density state variable of gas , change in density during process governed laws of thermodynamics. static gas, density same throughout entire container. density therefore scalar quantity. can shown kinetic theory density inversely proportional size of container in fixed mass of gas confined. in case of fixed mass, density decreases volume increases.