earth science

Standard atmosphere (unit)

Standard atmosphere (unit) is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Standard atmosphere (unit) rather than just read about it. In short: The standard atmosphere (symbol: atm) is a unit of pressure defined as 101325 Pa. It is sometimes used as a reference pressure or standard pressure.

Key takeaways

Standard atmosphere (unit) belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Standard atmosphere (unit) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Standard atmosphere (unit) from memory before moving on to harder problems.

Reference excerpt

The standard atmosphere (symbol: atm) is a unit of pressure defined as 101325 Pa. It is sometimes used as a reference pressure or standard pressure. It is approximately equal to Earth's average atmospheric pressure at sea level.

History The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0 °C (32 °F) and standard gravity (gn = 9.80665 m/s2). It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure. In 1954, the 10th General Conference on Weights and Measures (CGPM) adopted standard atmosphere for general use and affirmed its definition of being precisely equal to 1013250 dynes per square centimetre (101325 Pa). This defined pressure in a way that is independent of the properties of any particular substance. In addition, the CGPM noted that there had been some misapprehension that the previous definition (from the 9th CGPM) "led some physicists to believe that this definition of the standard atmosphere was valid only for accurate work in thermometry." In chemistry and in various industries, the reference pressure referred to in standard temperature and pressure was commonly 1 atm (101.325 kPa) prior to 1982, but standards have since diverged; in 1982, the International Union of Pure and Applied Chemistry recommended that for the purposes of specifying the physical properties of substances, standard pressure should be precisely 100 kPa (1 bar).

Pressure units and equivalencies

A pressure of 1 atm can also be stated as:

≈ 1.033 kgf/cm2 ≈ 10.33 m H2O ≈ 760 mmHg

≈ 29.92 inHg ≈ 406.782 in H2O ≈ 2116.22 pounds-force per square foot (lbf/ft2) The notation ata has been used to indicate an absolute pressure measured in either standard atmospheres (atm) or technical atmospheres (at).

See also International Standard Atmosphere

References

Illustrations

Worked examples

Example 1 — a first encounter with Standard atmosphere (unit)

Start with the simplest possible case. Write down what Standard atmosphere (unit) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Standard atmosphere (unit) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Standard atmosphere (unit) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Standard atmosphere (unit)

In research: Standard atmosphere (unit) appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Standard atmosphere (unit) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Standard atmosphere (unit) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Atmospheric pressure, Units of pressure, so understanding it makes those chapters shorter.
In everyday life: Look for Standard atmosphere (unit) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Standard atmosphere (unit) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Standard atmosphere (unit) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Standard atmosphere (unit) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Standard atmosphere (unit) in simple terms?

The standard atmosphere (symbol: atm) is a unit of pressure defined as 101325 Pa. It is sometimes used as a reference pressure or standard pressure.

Why does Standard atmosphere (unit) matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Standard atmosphere (unit)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Standard atmosphere (unit).