science

Centimetre or millimetre of water

Centimetre or millimetre of water is a 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 Centimetre or millimetre of water rather than just read about it. In short: A centimetre or millimetre of water (US spelling centimeter or millimeter of water) are less commonly used measures of pressure based on the pressure head of water. Centimetre of water A centimetre of water is a unit of pressure.

Key takeaways

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

Reference excerpt

A centimetre or millimetre of water (US spelling centimeter or millimeter of water) are less commonly used measures of pressure based on the pressure head of water.

Centimetre of water

A centimetre of water is a unit of pressure. It may be defined as the pressure exerted by a column of water of 1 cm in height at 4 °C (temperature of maximum density) at the standard acceleration of gravity, so that 1 cmH2O (4°C) = 999.9720 kg/m3 × 9.80665 m/s2 × 1 cm = 98.063754138 Pa ≈ 98.0638 Pa, but conventionally a nominal maximum water density of 1000 kg/m3 is used, giving 98.0665 Pa. The centimetre of water unit is frequently used to measure the central venous pressure, the intracranial pressure while sampling cerebrospinal fluid, as well as determining pressures during mechanical ventilation or in water supply networks (then usually in metres water column). It is also a common unit of pressure in the speech sciences. This unit is commonly used to specify the pressure to which a CPAP machine is set after a polysomnogram.

Millimetre of water

Millimetre of water (US spelling millimeter of water) is a unit of pressure. It may be defined as the pressure exerted by a column of water of 1 mm in height at 4 °C (temperature of maximum density) at the standard acceleration of gravity, so that 1 mmH2O (4 °C) = 999.9720 kg/m3 × 9.80665 m/s2 × 1 mm = 9.8063754138 Pa ≈ 9.80638 Pa, but conventionally a nominal maximum water density of 1000 kg/m3 is used, giving 9.80665 Pa.

In limited and largely historic contexts it may vary with temperature, using the equation:

P = ρ·g·h/1000, where P: pressure in Pa ρ: density of water (conventionally 1000 kg/m3 at 4 °C) g: acceleration due to gravity (conventionally 9.80665 m/s2 but sometimes locally determined) h: water height in millimetres. The unit is often used to describe how much water rainwear or other outerwear can take or how much water a tent can resist without leaking.

See also Inch of mercury Inch of water Millimetre of mercury

References

External links Pressure conversion calculator at Cornell University website

Worked examples

Example 1 — a first encounter with Centimetre or millimetre of water

Start with the simplest possible case. Write down what Centimetre or millimetre of water claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Centimetre or millimetre of water 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 Centimetre or millimetre of water 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 Centimetre or millimetre of water

In research: Centimetre or millimetre of water appears in 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 Centimetre or millimetre of water 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: Centimetre or millimetre of water is common in secondary-school and first-year university syllabi. It links to neighbouring topics Units of pressure, so understanding it makes those chapters shorter.
In everyday life: Look for Centimetre or millimetre of water 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 Centimetre or millimetre of water in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Centimetre or millimetre of water 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 Centimetre or millimetre of water out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Centimetre or millimetre of water in simple terms?

A centimetre or millimetre of water (US spelling centimeter or millimeter of water) are less commonly used measures of pressure based on the pressure head of water. Centimetre of water A centimetre of water is a unit of pressure.

Why does Centimetre or millimetre of water matter?

Because it connects several 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 Centimetre or millimetre of water?

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 Centimetre or millimetre of water.