Air pressure in the context of Vacuum flush

Contrails (/ˈkɒntreɪlz/; short for "condensation trails") or vapour trails are line-shaped clouds produced by aircraft engine exhaust or changes in air pressure, typically at aircraft cruising altitudes several kilometres/miles above the Earth's surface. They are composed primarily of water, in the form of ice crystals. The combination of water vapor in aircraft engine exhaust and the low ambient temperatures at high altitudes cause the trails' formation.

Impurities in the engine exhaust from the fuel, including soot and sulfur compounds (0.05% by weight in jet fuel) provide some of the particles that serve as cloud condensation nuclei for water droplet growth in the exhaust. If water droplets form, they can freeze to form ice particles that compose a contrail. Their formation can also be triggered by changes in air pressure in wingtip vortices, or in the air over the entire wing surface. Contrails, and other clouds caused directly by human activity, are called homogenitus.

In digital recording, an audio or video signal is converted into a stream of discrete numbers representing the changes over time in air pressure for audio, or chroma and luminance values for video. This number stream is saved to a storage device. To play back a digital recording, the numbers are retrieved and converted back into their original analog audio or video forms so that they can be heard or seen.

In a properly matched analog-to-digital converter (ADC) and digital-to-analog converter (DAC) pair, the analog signal is accurately reconstructed, within the constraints of the Nyquist–Shannon sampling theorem, which dictates the sampling rate and quantization error dependent on the audio or video bit depth. Because the signal is stored digitally, assuming proper error detection and correction, the recording is not degraded by copying, storage or interference.

The field of articulatory phonetics is a subfield of phonetics that studies articulation and ways that humans produce speech. Articulatory phoneticians explain how humans produce speech sounds via the interaction of different physiological structures. Generally, articulatory phonetics is concerned with the transformation of aerodynamic energy into acoustic energy. Aerodynamic energy refers to the airflow through the vocal tract. Its potential form is air pressure; its kinetic form is the actual dynamic airflow. Acoustic energy is variation in the air pressure that can be represented as sound waves, which are then perceived by the human auditory system as sound.

A sea breeze or onshore breeze is a wind that blows in the afternoon from a large body of water toward or onto a landmass. By contrast, a land breeze or offshore breeze is a wind that blows in the night from a landmass toward or onto a large body of water. Sea breezes and land breezes are both important factors in coastal regions' prevailing winds.

Sea breeze and land breeze develop due to differences in air pressure created by the differing heat capacities of water and dry land. As such, sea breezes and land breezes are more localised than prevailing winds. Since land heats up much faster than water under solar radiation, a sea breeze is a common occurrence along coasts after sunrise. On the other hand, dry land also cools faster than water without solar radiation, so the wind instead flows from the land towards the sea when the sea breeze dissipates after sunset.

A barometer is a scientific instrument that is used to measure air pressure. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, pressure systems and frontal boundaries.

Barometers and pressure altimeters (the most basic and common type of altimeter) are essentially the same instrument, but used for different purposes. A pressure altimeter is used to estimate altitude by measuring the pressure of the atmosphere surrounding the altimeter and comparing the result to the expected atmospheric pressure at various altitudes, while a barometer is kept at a constant altitude and measures subtle pressure changes caused by weather and elements of weather. The average atmospheric pressure on the Earth's surface varies between 940 and 1040 hPa (mbar). The average atmospheric pressure at sea level is 1013 hPa (mbar).

A pressure suit is a protective suit worn by high-altitude pilots who may fly at altitudes where the air pressure is too low for an unprotected person to survive, even when breathing pure oxygen at positive pressure. Such suits may be either full-pressure (e.g., a space suit) or partial-pressure (as used by aircrew). Partial-pressure suits work by providing mechanical counter-pressure to assist breathing at altitude.

In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time. Periodic waveforms repeat regularly at a constant period. The term can also be used for non-periodic or aperiodic signals, like chirps and pulses.

In electronics, the term is usually applied to time-varying voltages, currents, or electromagnetic fields. In acoustics, it is usually applied to steady periodic sounds — variations of pressure in air or other media. In these cases, the waveform is an attribute that is independent of the frequency, amplitude, or phase shift of the signal.

An air blaster or air cannon is a de-clogging device with two main components: a pressure vessel (storing air pressure) and a triggering mechanism (high speed release of compressed air). They are permanently installed on silos, bins and hoppers for powdery materials, and are used to prevent caking and to allow maximum storage capacity. They are also used in the film and theatre industries to project simulated debris from explosions, and as surprise effects in Halloween haunts and other attractions.

Air blasters do not need any specific air supply. Available plant air is enough with a minimum of 4 bar air pressure (60 psi or 400 kPa), although 5 to 6 bar are preferred for better results (75 to 90 psi). The average air consumption is moderate, and depends on the number of firings per hour, size of the pressure vessel, and number of blasters installed. For instance, a 50-liter air blaster consumes 0.60 normal cubic metres per hour at 6 bar air pressure (90 psi or 600 kPa), with 2 firings per hour.

In fluid mechanics, the pressure-gradient force is the force that results when there is a difference in pressure across a surface. In general, a pressure is a force per unit area across a surface. A difference in pressure across a surface then implies a difference in force, which can result in an acceleration according to Newton's second law of motion, if there is no additional force to balance it. The resulting force is always directed from the region of higher-pressure to the region of lower-pressure. When a fluid is in an equilibrium state (i.e. there are no net forces, and no acceleration), the system is referred to as being in hydrostatic equilibrium. In the case of atmospheres, the pressure-gradient force is balanced by the gravitational force, maintaining hydrostatic equilibrium. In Earth's atmosphere, for example, air pressure decreases at altitudes above Earth's surface, thus providing a pressure-gradient force which counteracts the force of gravity on the atmosphere.

A virga, also called a dry storm, is an observable streak or shaft of precipitation that evaporates or sublimates before reaching the ground. A shaft of precipitation that does not evaporate before reaching the ground is known in meteorology as a precipitation shaft. At high altitudes, precipitation falls mainly as ice crystals before melting and finally evaporating. This is often due to compressional heating, because air pressure increases closer to the ground. Virga is very common in deserts and temperate climates. In North America, it is commonly seen in the Western United States and the Canadian Prairies. It is also very common in the Middle East, Australia, and North Africa.

Virgae can cause varying weather effects because as rain is changed from liquid to vapor form it removes significant amounts of heat from the air due to water's high heat of vaporization. Precipitation falling into these cooling downdrafts may eventually reach the ground. In some instances these pockets of colder air can descend rapidly, creating a wet or dry microburst which can be extremely hazardous to aviation. Conversely, precipitation evaporating at high altitude can compressionally heat as it falls, and result in a gusty downburst which may substantially and rapidly warm the surface temperature. This fairly rare phenomenon, a heat burst, also tends to be of exceedingly dry air.

In fluid mechanics the term static pressure refers to a term in Bernoulli's equation written as static pressure + dynamic pressure = total pressure. Since pressure measurements at any single point in a fluid always give the static pressure value, the 'static' is often dropped.In the design and operation of aircraft, static pressure is the air pressure in the aircraft's static pressure system.