Question 1

Why does Britain still use miles per hour?

Accepted Answer

Road signage and speed limits were left out of metrication. Changing every sign in the country was judged too expensive and too disruptive, so mph remained the legal standard while almost everything else went metric.

Question 2

What is a knot, and why not just say miles per hour?

Accepted Answer

A knot is one nautical mile per hour, and a nautical mile is one minute of latitude. That makes it directly readable off a chart: a vessel doing ten knots covers ten minutes of latitude in an hour, which no land unit can tell you.

Question 3

Where does the word knot come from?

Accepted Answer

Sailors trailed a weighted log on a line knotted at fixed intervals, then counted how many knots ran through their hands against a sand glass. The count was the speed, and the name stuck.

Question 4

Is Mach 1 always the same speed?

Accepted Answer

No. Mach is a ratio against the local speed of sound, which falls as air gets colder. Mach 1 is about 761 mph at sea level but nearer 660 mph in the thin cold air at cruising altitude.

Question 5

Is furlongs per fortnight a real unit?

Accepted Answer

It is a real calculation and a deliberate joke. Physics and engineering lecturers use it to show that dimensional analysis works regardless of how absurd the units are. One furlong per fortnight is roughly 0.0001 miles per hour.

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