Question 1

Why do some countries still use inches?

Accepted Answer

The US, the UK (partly), and Canada inherited the British imperial system, while Russia and most of the world use metric. Inches survive in specific niches everywhere: TV and smartphone screen diagonals, pipe threads, and a person's height in the US (feet and inches).

Question 2

How long is one inch?

Accepted Answer

Exactly 2.54 cm (the 1959 definition). 12 inches make a foot, 3 feet a yard, and 1,760 yards a mile. For screens, a 15.6″ diagonal is 39.6 cm and 6.7″ is 17 cm.

Question 3

What is a nautical mile?

Accepted Answer

A nautical mile is exactly 1,852 m — one arcminute of latitude along a meridian. Do not confuse it with the land mile (1,609 m). A knot is one nautical mile per hour ≈ 1.852 km/h. Aviation and shipping use nautical miles.

Question 4

How can I convert quickly in my head?

Accepted Answer

Kilometres to miles: divide by 1.6. Miles to km: multiply by 1.6. Centimetres to inches: divide by 2.54 (roughly ÷2.5). Metres to feet: multiply by 3.28 (roughly ×3). So 180 cm ≈ 5 ft 11 in.

Question 5

What is an angstrom for?

Accepted Answer

An angstrom (Å) is 10⁻¹⁰ m = 0.1 nm. Atoms span about 0.3–3 Å and visible light has wavelengths of 4,000–7,000 Å. In crystallography, chemistry, and optics the angstrom is sometimes handier than the nanometre.

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