Atmospheric Pressure (atm): A Unit of Pressure with Real Life Examples

Atmosphere (atm) is a unit of measurement used to quantify pressure, specifically the pressure exerted by the Earth’s atmosphere. One atmosphere is approximately equal to the pressure exerted by a column of mercury that is about one meter high at sea level. It’s like the weight of the air around us pressing down on everything.
For instance, at sea level, we typically experience an atmospheric pressure of around 1 atm, and this pressure is vital for various processes in our daily lives.
In practical terms, when scuba diving, the pressure increases as you go deeper into the water. At a depth of 10 meters underwater, the pressure is about 2 atm, exerting twice the pressure we experience at the surface. Similarly, weather reports often mention atmospheric pressure in atm, affecting our daily plans and activities.

Real Life Examples of atm Pressure

1. Weather Forecasts: Typically around 1 atm (at sea level).
2. Vacuum Sealing Food: Creating a pressure lower than 1 atm inside the packaging.
3. Scuba Diving: Varies with depth, e.g., about 2 atm at 10 meters underwater.
4. Altitude and Air Travel: Decreases with altitude, e.g., around 0.7 atm on a high mountain.
5. Canning and Food Preservation: Creating pressures similar to or slightly higher than 1 atm inside sealed containers.

Mathematical Relations of 1 atm

A table that includes conversions of 1 atmosphere (atm) to various units of pressure, along with daily life examples for better understanding:

Case Study

Title: Designing Pressure Systems for a Satellite Propulsion System with 30 Atmospheres (atm) Pressure

Background: Engineering students are tasked with designing pressure systems for a satellite propulsion system that utilizes a specific chemical propellant. The propulsion system requires maintaining a pressure of 30 atmospheres (atm) within the propellant tanks for efficient thrust generation.

Design Requirements:

1. Pressure: 30 atm (atm to Pa: 1 atm=101,325 Pa)
2. Safety factor: 2.0

Steps:

1. Pressure in Pascals (Pa): 30 atm=30×101,325 Pa=3,039,750 Pa
2. Material Strength Analysis: Research materials with suitable yield and ultimate strengths suitable for the pressure requirements. Assume a material with yield strength (σyield) of 400 MPa.
3. Structural Design: Calculate the required thickness (t) of the tank using the formula: t=P×r^2×σyield×Safety Factor
   where P is pressure in Pa, r is the radius of the tank.
4. Safety Measures: Incorporate pressure relief valves and rupture discs to maintain pressure within the safe limits and avoid any catastrophic failures.

In summary, the students will calculate pressure in Pascals, analyze material strength, design the pressure vessels structurally, and implement safety measures for an effective and reliable pressure system for the satellite’s propulsion system operating at 30 atmospheres (atm).

Derive 1atm = 101325 Pascals

• 1 Pascal (Pa) is 1 Newton per square meter (1 Pa=1 N/m2).
• 1 atmosphere (atm) is the pressure exerted by a 760 mm column of mercury at 0 degrees Celsius.
• We can calculate this pressure using the density of mercury (ρHg) and acceleration due to gravity (g)
• Pressure in atm=ρHg×g×height of mercury column
• Given the density of mercury is approximately 13,595 kg/m3 and g≈9.81 m/s2, and the height is 760 mm (0.76 m)
• Pressure in atm=13,595×9.81×0.76N/m2=101,325N/m2=101,325Pa

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