Informally, a tangle of string is called a knot, although in mathematics a knot is a loop, having no beginning and no end, and is hence an embedding of a simple circle into three dimensional space. Knot theory asks whether one embedding can be smoothly transformed into another, and is therefore an area of topology.

Alternatively, a speed of one nautical mile per hour is called a "knot". In trying to estimate one's position by use of dead reckoning, speeds were estimated by throwing a lump of wood (the log) into the water, letting the string run out, and counting how many knots passed through the fingers in a given time. Originally the knots were 7 fathoms (42 feet) apart and the timer was 30 seconds, but this was later changed to 47'3" and 28 seconds respectively.

Exercise: What two speeds do these settings correspond to?

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