science

FFF system

FFF system 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 FFF system rather than just read about it. In short: The furlong–firkin–fortnight (FFF) system is a humorous system of units based on unusual or impractical measurements. The length unit of the system is the furlong, the mass unit is the mass of a firkin of water, and the time unit is the fortnight.

Key takeaways

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

Reference excerpt

The furlong–firkin–fortnight (FFF) system is a humorous system of units based on unusual or impractical measurements. The length unit of the system is the furlong, the mass unit is the mass of a firkin of water, and the time unit is the fortnight. Like the SI or metre–kilogram–second systems, there are derived units for velocity, volume, mass and weight, etc. It is sometimes referred to as the FFFF system where the fourth 'F' is degrees Fahrenheit for temperature. While the FFF system is not used in practice, it has been used as an example in discussions of the relative merits of different systems of units. Some of the FFF units, notably the microfortnight, have been used jokingly in computer science. The derived unit furlongs per fortnight has served frequently in classroom examples of unit conversion and dimensional analysis.

Base units and definitions

Multiples and derived units

Microfortnight and other decimal prefixes One microfortnight is equal to 1.2096 seconds. This has become a joke in computer science because in the VMS operating system, the TIMEPROMPTWAIT variable, which holds the time the system will wait for an operator to set the correct date and time at boot if it realizes that the current value is invalid, is set in microfortnights. This is because the computer uses a loop instead of the internal clock, which has not been activated yet to run the timer. The documentation notes that "[t]he time unit of micro-fortnights is approximated as seconds in the implementation". The Jargon File reports that the millifortnight (about 20 minutes) and nanofortnight have been occasionally used.

Furlong per fortnight One furlong per fortnight is a speed that would be barely noticeable to the naked eye. It converts to:

1.663×10−4 m/s, (i.e. 0.1663 mm/s) roughly 1 cm/min (to within 1 part in 400) 5.987×10−4 km/h roughly 3⁄8 in/min 3.720×10−4 mph the speed of the tip of a 3+3⁄4 inch minute hand

Speed of light The speed of light is 1.8026×1012 furlongs per fortnight (1.8026 terafurlongs per fortnight). By mass–energy equivalence, 1 firkin is equal to 3.24936676×1024 firkin·⁠furlong2/fortnight2⁠ (≈ 3.478×1015 BTU, or 3.669×1018 joules).

Others In the FFF system, heat transfer coefficients are conventionally reported as BTU per foot-fathom per degree Fahrenheit per fortnight. Thermal conductivity has units of BTU per fortnight per furlong per degree Fahrenheit. The furlong per fortnight and firkin per fortnight can refer to "any obscure unit".

See also List of unusual units of measurement List of humorous units of measurement

Footnotes

References

Worked examples

Example 1 — a first encounter with FFF system

Start with the simplest possible case. Write down what FFF system 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 FFF system 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 FFF system 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 FFF system

In research: FFF system 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 FFF system 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: FFF system is common in secondary-school and first-year university syllabi. It links to neighbouring topics Systems of units, Technology humour, so understanding it makes those chapters shorter.
In everyday life: Look for FFF system 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 FFF system in 20 minutes

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

Frequently asked questions

What is FFF system in simple terms?

Why does FFF system 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 FFF system?

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 FFF system.