Resistance of air

In this approach, a body is thrown up and then it falls along the same path. Observations are made in passing two fixed positions during the movement up and down, Fig. 3.2b. Of course, inside the cylinder where the movement takes place, there is always some air, but this approach allows us to reduce its influence better than in the previous method. This is related to the fact that the resistance of air is the same during motion in the different directions. However, in one case the friction force and field g have the same direction, while in the second case they are opposite to each other. In the symmetrical approach we measure moments when a mass passes the upper and lower stations. The point 0 is origin that corresponds to the highest position of the body where... 

Table 1.25 Freeze-thaw resistance of air-trained concrete containing water-reducing admixtures...

In the early days of the use of superplasticized concrete, some concerns were aired regarding the resistance of air-entrained concrete containing superplasticizers to freeze-thaw cycling. However, more recent research has indicated the following ... 

In earlier works on aerodynamics, it was believed that the resistance of air was a... 

Sarrau diaproved this and stated that the resistance of air is a function of a certain value, now known as the "Mach Number" (nombre de Mach, in French)... 

Droplet size. Big droplets settle faster than little droplets. Contrary to that nonsense we were taught in school, cannon balls do drop faster then BBs—if one accounts for the resistance of air (BBs are small spheres of lead shot used in air guns). 

Due to the fact that Hugoniot was the first to formulate the laws of the resistance of air to the flight of projectiles, he is generally considered as the founder of the modem science of "aerodynamics. The principles of aerodynamics are also applied to aeronautics... 

The motion of aerosol droplets following space spraying is governed by gravity and the resistance of air particle motion. Droplet settlement depends on the size of the droplet. The droplet settling velocity (Vi) (m/s) is given by Stokes law (Hinds, 1982) ... 

Convection is called forced convection if Ihe fluid is forced to flow over the surface by external means such as a fan, pump, or the wind. In contrast, convection is called natural (or free) convection if the fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid (Fig. 1 33). For example, in the absence of a fan, heat transfer from the surface of the hot block in Fig. 1-32 is by natural convection since any motion in the air in this case is due to the rise of Ihe warmer (and thus lighter) air near the surface and the fall of the cooler (and thus heavier) air to fill its place. Heat transfer between the block and the surrounding air is by conduction if the temperature difference between Ihe air and the block is not large enough to overcome the resistance of air to movement and thus to initiate natural convection currents. 

Overcoming the resistance of air cooler should be considered in selecting the type of local driving fan because air cooler is not motivated by itself. Metal hose is adopted to connect air cooler water pipes with main pipe of refrigerant water. 

After leaving the aperture the jet disintegrates due to air resistance and vaporization. Assuming that disintegration is caused by the resistance of air we obtain the erosion velocity Ue... 

The trajectory of the missile is calculated in two dimensions accoimting for a resistance of air proportional to the square of flight velocity. This applies to the so-called ballistic range which lies between very low velocities, where resistance is proportional to velocity, and supersonic velocities where resistance is a complex function. Fragments from vessel bursts are usually encountered in this range [2]. We then have the following equations of motion... 

If the usual model, which does not account for the resistance of air, is used we obtain the following results ... 

Comparison of the results suggests that the resistance of air should not be neglected when treating missile flight. 

The presence of potassium soaps in resins synthesised from crude sucrose esters had an adverse effect on the water resistance of air-dried films. The gloss of paints also was reduced. Improved performance was noted using soap-free sucrose esters or, particularly, the products obtained by extraction of these materials with methanol to remove the more hydrophilic mono- and disubstituted sucrose esters, free fatty acids emd unreacted methyl esters. 

Since the thermal resistance of air is higher than fibers, fiber has little influence on fabric thermal resistance, therefore insulated properties of fabric in a dry state. When a fabric becomes wet, the role of fiber on thermal resistance may become more important because of the low thermal resistance of wato-. As water saturates inte-yam spaces, air in these spaces is displaced, reducing the contribution of air and increasing the contribution of moisture transport of the fibers to the thermal resistance of a fabric. The thermal conductivity of wet fabrics is increased with increased moisture content. The sorption properties of a particular fibo", ie, hydrophihc and hydrophobic, influence the rapid thermal conductivity increase at the initial stage thereafter the increase of thermal conductivity with increasing wato" content behaves similarly for all fibo" types [25—27]. 

Important methods for the determination of the specific surface area and of the pore size distribution are based on the measurement of the gas adsorption isotherm [1,2]. The gas adsorption method and the evaluation according to Brunauer, Emmett and Teller using the two-parameter BET equation has been standardized in several countries for a number of years and an ISO standard just appeared. To establish the pore size distribution the method of Barrett, Joyner and Halenda (BJH) is generally accepted. Other methods for this purpose make use of the flow resistance of air through the compressed sample. The Blaine test and other flow tests used to characterize building materials are standardized world-wide. 

Fluid friction refers to air, water, or other types of fluid providing the resistance to movement between two objects. One example of fluid friction would be the resistance of air to an airplane flying. Another example would be the torque converter in an automatic transmission the transmission fluid provides the power to drive the automobile through jfriction with the impeller blades. 

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