Pound (force) in the context of "Pressures"

Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.

In most circumstances, atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so atmospheric pressure decreases with increasing elevation. Because the atmosphere is thin relative to the Earth's radius—especially the dense atmospheric layer at low altitudes—the Earth's gravitational acceleration as a function of altitude can be approximated as constant and contributes little to this fall-off. Pressure measures force per unit area, with SI units of pascals (1 pascal = 1 newton per square metre, 1 N/m). On average, a column of air with a cross-sectional area of 1 square centimetre (cm), measured from the mean (average) sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons, resulting in a pressure of 10.1 N/cm or 101 kN/m (101 kilopascals, kPa). A column of air with a cross-sectional area of 1 in would have a weight of about 14.7 lbf, resulting in a pressure of 14.7 lbf/in.

Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled gage pressure) is the pressure relative to the ambient pressure.

Various units are used to express pressure. Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m); similarly, the pound-force per square inch (psi, symbol lbf/in) is the traditional unit of pressure in the imperial and US customary systems. Pressure may also be expressed in terms of standard atmospheric pressure; the unit atmosphere (atm) is equal to this pressure, and the torr is defined as 1⁄760 of this. Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.

The short ton (abbreviation: tn or st), also known as the US ton, is a measurement unit equal to 2,000 pounds (907.18 kg). It is commonly used in the United States, where it is known simply as a ton; however, the term is ambiguous, the single word "ton" being variously used for short, long, and metric tons.

The various tons are defined as units of mass. They are sometimes used as units of weight, the force exerted by a mass at standard gravity (e.g., short ton-force). One short ton exerts a weight at one standard gravity of 2,000 pound-force (lbf).

The specific weight, also known as the unit weight (symbol γ, the Greek letter gamma), is a volume-specific quantity defined as the weight W divided by the volume V of a material:$${\displaystyle \gamma ={\frac {W}{V}}\ .}$$Equivalently, it may also be formulated as the product of density, ρ, and gravity acceleration, g: $${\displaystyle \gamma =\rho \,g.}$$Its unit of measurement in the International System of Units (SI) is the newton per cubic metre (N/m), expressed in terms of base units as kg⋅m⋅s.A commonly used value is the specific weight of water on Earth at 4 °C (39 °F), which is 9.807 kilonewtons per cubic metre or 62.43 pounds-force per cubic foot.

The Space Shuttle Solid Rocket Booster (SRB) was the first solid-propellant rocket to be used for primary propulsion on a vehicle used for human spaceflight. A pair of them provided 85% of the Space Shuttle's thrust at liftoff and for the first two minutes of ascent. After burnout, they were jettisoned, and parachuted into the Atlantic Ocean, where they were recovered, examined, refurbished, and reused.

The Space Shuttle SRBs were the most powerful solid rocket motors to ever launch humans. The Space Launch System (SLS) SRBs, adapted from the shuttle, surpassed it as the most powerful solid rocket motors ever flown, after the launch of the Artemis 1 mission in 2022. Each Space Shuttle SRB provided a maximum 14.7 MN (3,300,000 lbf) thrust, roughly double the most powerful single-combustion chamber liquid-propellant rocket engine ever flown, the Rocketdyne F-1. With a combined mass of about 1,180 metric tons (2,600,000 lb), they comprised over half the mass of the Shuttle stack at liftoff.