Name: atmospheric pressure and altitude
Uploaded: 2025-05-22T09:06:09.000Z
Duration: 1 min 18 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Systems

ESS.EES.2.5

Variation of Atmospheric Pressure

La Tierra está envuelta por capas de aire, conocidas como atmósfera. Es arrastrado hacia la superficie por la gravedad y ejerce una presión conocida como presión atmosférica.
La presión atmosférica cambia con la altura y se puede dar en términos del peso o la densidad del aire. Sin embargo, según la ley de los gases ideales, la densidad también depende de la presión.
Suponiendo que la temperatura del aire y la aceleración debida a la gravedad permanecen constantes con la altura y sustituyendo la expresión por la densidad y reorganizando la ecuación, se puede obtener la tasa de cambio de presión con la altura.
Aquí, las cantidades constantes dentro de los paréntesis se denominan alfa.
A continuación, se integra la ecuación a partir del nivel del mar y se resuelve para obtener la relación de la presión con la altura: la fórmula barométrica.
Al considerar las moléculas de nitrógeno a 300 kelvin, se puede obtener un valor aproximado de uno sobre alfa, una longitud característica conocida como altura de la escala de presión. 
La presión atmosférica desciende exponencialmente por un factor de uno sobre e por cada 8.800 metros sobre el nivel del mar.

<ol>
	<li>OpenStax. (2019). Física Universitaria Vol. 1. [Versión web]. Recuperado de la sección 14.1 pp- 696 <a href="https://openstax.org/books/university-physics-volume-1/pages/14-1-fluids-density-and-pressure">https://openstax.org/books/university-physics-volume-1/pages/14-1-fluids-density-and-pressure</a></li>
</ol>

variación de la presión atmosférica

El cambio en la presión atmosférica con la altura es particularmente interesante. La disminución en la presión atmosférica con el aumento de la altitud se debe a la disminución de la fuerza gravitacional por unidad de área a medida que nos alejamos de la superficie de la tierra. Suponiendo que la temperatura del aire es constante a una altitud dada y que la ley de los gases ideales de la termodinámica describe la atmósfera de manera aproximada, podemos encontrar la variación de la presión atmosférica con la altura. Sea p(y) la presión atmosférica a una altura y. La densidad ρ en y, la temperatura T en la escala Kelvin (K) y la masa m de una molécula de aire están relacionadas con la presión absoluta por la ley de gases ideales, en la forma: <img alt="Equation1" src="/files/ftp_upload/14711/14711_Equation_1.svg" style="text-align: center; height: 38px;"> Utilizando la densidad de la ley de gases ideales, se integra la tasa de variación de la presión con la altura desde el nivel del mar, y se obtiene la expresión final: <img alt="Equation2" src="/files/ftp_upload/14711/14711_Equation_2.svg" style="text-align: center; height: 17px;"> donde, <img alt="Equation3" src="/files/ftp_upload/14711/14711_Equation_3.svg" style="text-align: center; height: 38px;"> La presión atmosférica disminuye exponencialmente con la altura, ya que el eje y apunta hacia arriba desde el suelo, y y tiene valores positivos en la atmósfera por encima del nivel del mar. La presión disminuye en un factor de 1/e cuando la altura es de 1/α, lo que nos da una interpretación física para α. La constante 1/α es una escala de longitud que caracteriza cómo varía la presión con la altura y a menudo se le llama altura de escala de presión.

Variación de la Presión Atmosférica

El cambio en la presión atmosférica con la altura es particularmente interesante. La disminución de la presión atmosférica con el aumento de la altitud se debe a la ...

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Education

Educación

JoVE Core

Physics

Física

Unit 1

Unidad 1

Fluid Mechanics

Mecánica de fluidos

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

atmospheric pressure and altitude

Atmospheric pressure and altitude are closely linked. As height increases, atmospheric pressure decreases. This happens because the gravitational force per unit area becomes smaller as we move away from Earth’s surface.

To describe this change, the atmosphere is treated with a constant air temperature at a given altitude. The ideal gas law of thermodynamics is also used as a good approximation for the air. Let p(y) be the atmospheric pressure at height y. The density ρ at y, the temperature T in Kelvin, and the mass m of an air molecule are related to absolute pressure by the ideal gas law.

Using the density from the ideal gas law, the rate of change of pressure with height can be integrated from sea level. The result shows that atmospheric pressure drops exponentially with height. Since the y-axis points upward from the ground, y has positive values above sea level in the atmosphere.

The pressure drops by a factor of 1/e when the height reaches 1/α. This gives a physical meaning to α. The constant 1/α is a length scale that describes how pressure changes with height, and it is often called the pressure scale height.

Atmospheric Pressure and Altitude

characteristics of fluids

Fluid Behavior Under Force

Fluid behavior under force differs from the behavior of solids. When a force acts parallel to the top surface of a solid, the solid resists it because of internal friction between its layers. This is called shearing resistance. If the force is removed, the shearing forces help the solid return to its original shape. Other deformation forces can also change the shape of a solid for a short time, as long as the force stays below a threshold magnitude. Solids usually keep their shape, which makes...

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density

Density, Floating, and Specific Gravity

Density helps explain why objects sink or float in a fluid. It is also useful for identifying a substance and for learning about its phase and substructure. The SI unit of density is kg/m3, and the cgs unit is g/cm3. Liquids and solids usually have densities that are roughly comparable. That matches the fact that their atoms are in close contact. Gases have much lower densities than liquids and solids because their atoms are separated by large amounts of empty space. Density does not always...

pressure of fluids

Fluid Pressure in Everyday Life

Fluid pressure appears in many everyday situations, including blood pressure and weather systems. The same force can have a very different effect depending on the area it acts on. A force spread over 1 mm² creates 100 times more pressure than the same force spread over 1 cm². That is why a sharp needle can pierce skin with a small force, while the same force from a finger usually does not. Pressure is especially important when studying fluids. A fluid does not offer much resistance to a force...

variation of atmospheric pressure

Atmospheric pressure and altitude are closely linked. As height increases, atmospheric pressure decreases. This happens because the gravitational force per unit area becomes smaller as we move away from Earth’s surface. To describe this change, the atmosphere is treated with a constant air temperature at a given altitude. The ideal gas law of thermodynamics is also used as a good approximation for the air. Let p(y) be the atmospheric pressure at height y. The density ρ at y, the temperature T...

pascal's law

Pascal’s Principle in Static Fluids

Pascal’s principle explains how pressure changes move through a fluid that is not flowing. A fluid at rest is in static equilibrium. If the fluid is water, it is in hydrostatic equilibrium. In this state, the net force on any part of the fluid must be zero, or the fluid will begin to flow. Blaise Pascal described this idea in 1653 in Treatise on the Equilibrium of Liquids. He showed that when pressure changes in an enclosed fluid, that change is transmitted without loss through the fluid and...

application of pascal's law

Hydraulic Force Transfer with Pascal's Law

Hydraulic force transfer uses Pascal's law to move pressure through an enclosed fluid. Pascal showed experimentally that a change in pressure applied to a confined fluid is transmitted undiminished throughout the fluid and to the walls of its container. That idea is the basis of hydraulics, a major part of modern mechanical technology. Hydraulic systems appear in automotive brakes, hydraulic jacks, and many other machines. A simple hydraulic system uses two pistons at the same height. Because...

pressure gauges

Gauge vs Absolute Pressure

Pressure gauges often show pressure relative to atmospheric pressure. Many gauges, including those on scuba tanks, are set to read zero at atmospheric pressure. That reading is called gauge pressure. When the pressure inside the tank is higher than atmospheric pressure, the gauge shows a positive value. Some gauges can also measure negative pressure. This is useful in a vacuum chamber, which is a rigid chamber where some air has been pumped out. Because the pressure inside the chamber is below...

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archimedes' principle

Buoyant Force from Fluid Pressure

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density and archimedes' principle

How Buoyancy Depends on Density

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accelerating fluids

Fluid Pressure in an Accelerating Elevator

Fluid pressure changes when a liquid accelerates inside a moving container. A beaker placed in an elevator that moves upward with constant acceleration is one example. In this setup, the pressure and buoyant force equations must be modified. To find the pressure difference, the liquid is modeled as a thin vertical cylinder with height h and an infinitesimal cross-sectional area, ΔS. Three vertical forces act on this small fluid element. The liquid below the bottom surface pushes upward, the...

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surface tension and surface energy

Why Liquids Form Drops and Float

Surface tension and surface energy explain why liquids behave the way they do at their surface. A paint brush moves freely in water, but its bristles stick together after it is taken out. That change is caused by surface tension. Inside a liquid, bulk molecules feel attractive forces from nearby molecules in all directions. At the surface, molecules feel a net downward pull from the molecules below them. Because of this imbalance, the liquid surface acts like a stretched membrane and tries to...

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excess pressure inside a drop and a bubble

excess-pressure-inside-a-drop-and-a-bubble

Surface Tension in Drops and Bubbles

Surface tension sets the pressure difference in small drops and bubbles. For a tiny liquid drop, gravity can be neglected, so the drop is treated as spherical. It can also be viewed as two equal hemispherical drops joined together by surface tension. The forces on the drop come from three sources. The liquid inside pushes outward, the air outside pushes inward, and surface tension acts along the diameter between the two hemispheres. Since surface tension is force per unit length, it creates a...

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buoyancy

Buoyant Force in Sinking and Floating

Buoyant force explains why objects float, sink, or stay suspended in a fluid. A fluid can be a liquid or a gas, and every object placed in it experiences this upward force. A metal ball sinks, while a rubber ball floats. A submarine also changes its buoyancy to move up or down. The force comes from pressure changes in the fluid. Fluid pressure increases with depth because the weight of the fluid above also increases. That means the bottom of an object feels more pressure than the top. This...

contact angle

Wetting and Surface Curvature

Wetting and surface curvature describe how a liquid behaves where it meets a solid. When a solid is dipped into a liquid, the liquid surface can bend near the contact line. In some cases, the liquid rises along the solid. In others, the surface becomes convex or depressed near the solid. This behavior comes from cohesive and adhesive forces. Adhesive force is the attraction between molecules of different materials, such as a solid and a liquid. Cohesive force is the attraction between...

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rise of liquid in a capillary tube

Capillary Action in Thin Tubes

Capillary action explains why liquid can rise or fall in a very thin tube compared with the liquid around it. A capillary is a narrow cylindrical tube, and the effect becomes noticeable when it is dipped into a liquid. The movement happens because two forces act in opposite directions. Cohesive forces make liquid molecules stick to each other, so the liquid tends to hold together and form a rounded shape. Adhesive forces pull the liquid toward the walls of the container. In a narrow glass...

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laminar and turbulent flow

Fluid Motion Patterns in Air and Water

Fluid dynamics studies fluids in motion. Scientists often use velocity vectors to show fluid motion in places like meteorology. For example, wind in the atmosphere can be mapped with vectors that show the speed and direction of the wind at each point. Another way to show fluid motion is with a streamline. A streamline shows the path of a small volume of fluid as it flows. When the flow changes with time, the streamlines do not match the flow lines. The fluid velocity is always tangential to...

equation of continuity

Fluid Flow in Narrowing Pipes

Fluid flow in a pipe is described by flow rate and average speed. Flow rate, or volume flow rate, is the amount of fluid that passes a point through an area in a given time. It depends on both how fast the fluid moves and the size and shape of the conduit. For a river or pipe, a greater speed usually means a greater flow rate. A larger cross-sectional area also increases flow rate. That is why the same fluid can move differently through conduits of different sizes. The relationship becomes...

bernoulli's equation

Fluid Pressure and Speed in Motion

Bernoulli's equation connects fluid pressure with fluid speed. It helps explain why moving fluids can create pressure changes in everyday situations. One example is when two trains pass each other quickly and seem to pull inward. The same effect can happen when two cars pass each other at high speed. As the air between the trains or cars speeds up, its pressure drops. The air on the outside stays at atmospheric pressure. That pressure difference creates a net inward force on the vehicles.

bernoulli's principle

Fluid Pressure and Speed Changes

Bernoulli's equation links fluid pressure and fluid speed in a static, incompressible fluid. For horizontal flow, where gravitational energy density stays constant, the equation is especially useful. In that setting, the result is known as Bernoulli's principle. Bernoulli's principle says that fluid pressure drops when speed increases, and pressure rises when speed decreases. This pressure-speed relationship helps explain how moving fluids behave in simple flow situations. It also provides a...

bernoulli's principle: applications

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Bernoulli's principle helps explain how many fluid devices work when the fluid moves at a constant height. It is useful for devices that use fast flow to create low pressure and for devices that measure fluid speed. Some devices use this pressure change to pull one fluid into another. These are called entrainment devices. A Bunsen burner uses an adjustable gas nozzle to entrain air for proper combustion. An atomizer uses a squeeze bulb to make a jet of air that pulls perfume drops into the...

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energy conservation and bernoulli's equation

energy-conservation-and-bernoulli-s-equation

Bernoulli’s Equation in Streamlined Flow

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viscosity

Viscosity and How Fluids Flow

Viscosity describes how easily a fluid flows. Water moves quickly, while honey and maple syrup flow slowly and stick to a surface. That difference comes from fluid friction between liquid layers and between a fluid and the material around it. In this example, water has a lower viscosity than honey and maple syrup. Viscosity is measured in newton-second per meter squared (N·s/m2) or pascal-second (Pa·s). It also changes with temperature and can differ from one fluid to another by several orders...

poiseuille's law and reynolds number

Fluid Resistance, Viscosity, and Flow Regime

Fluid resistance, viscosity, and flow regime shape how liquid moves through a horizontal tube. Fluid flows from high pressure to low pressure. The flow rate, Q, is the ratio of the pressure difference to the resistance in the tube. A larger pressure difference gives a higher flow rate. Poiseuille's law describes laminar flow of an incompressible fluid in a tube. In this relation, the factors that affect flow rate except pressure are grouped into resistance. Resistance depends on the tube size...

stokes' law

Terminal Velocity in a Viscous Fluid

Viscous forces act like friction in a liquid. They resist the relative motion of molecules and pull back on a solid body moving through the fluid. The size of this force depends on the body’s shape and size, its speed, and the liquid’s viscosity, density, and temperature. For a spherical solid object, the force in a fluid is described by Stokes’ law. This law applies only at low Reynolds number, when the flow is laminar and not turbulent. Experiments show that the force is proportional to the...

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key terms and concepts

See how atmospheric pressure decreases with altitude, why the drop is exponential, and what the pressure scale height tells us about the atmosphere.

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physics

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ESS.EES.3.4

Virginia  Standards of Learning

HIgh School

Earth Science

ES.11

ES.11.a

ES.12

ES.12.e

Alabama Course of Study Science

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9-12.ESS.2.7.e

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9-12.P.1.4

9-12.P.1.4.b

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Use models to explain how plate tectonics influence topography.

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ESS.EES.2.4

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Atmospheric Pressure and Altitude

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