Horsepower, PS and kilowatts, and where the torque and power curves cross
Car power is printed in mechanical horsepower, metric horsepower (PS) or kilowatts, three units that differ by small fix...
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The clock rule taught for crosswind reads high, most of all at sixty degrees
The crosswind on a runway is the wind speed times the sine of the angle between wind and runway, and flight training tea...
Warm water shifts a pipe's Reynolds number more than the laminar limits differ
Physics texts put the end of laminar pipe flow at a Reynolds number of 2,000 or 2,300, depending on the source, and Reyn...
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Jet lag by direction, worked through on routes out of Singapore and Hong Kong
Flying east asks the body clock to run earlier and flying west asks it to run later, and early estimates from real fligh...
Rebar weight by the d²/162 rule runs a fraction heavy against the standards
Rebar mass per metre is usually worked out as the bar's diameter in millimetres, squared, divided by 162. We checked tha...
An X chromosome comes from fewer ancestors than a family tree allows
A man's X chromosome can come only from his mother's side, while a woman's comes from both parents, so the ancestors who...
Shortcut WBGT formulas land on both sides of Singapore's measured heat stress
Singapore's official heat stress readings blend three thermometers, one of them in the sun. Checked against 30 MSS stati...
Humidity adds close to 400 feet to density altitude at Changi
Water vapour is lighter than dry air, so humid air raises density altitude even at a sea-level airport. At Changi's Apri...
Homebrew ABV formulas part ways once original gravity reaches 1.070
Homebrewers turn original and final gravity readings into alcohol by volume with one of two formulas, which agree closel...
The same wind speed can mean twice the pressure, depending on its averaging time
Wind pressure follows the square of the speed, so whether a figure is a 3-second gust or a 10-minute mean can more than...
Thunder covers a kilometre in under three seconds in Singapore air
Dividing the seconds between a lightning flash and its thunder by three gives kilometres, but in Singapore's air sound c...
Rare blood-group variants allow most of the child blood types a chart forbids
The textbook ABO rule forbids at least one child blood type for every pairing of parent types except A with B. Rare inhe...
NParks allows about twice the time Naismith's rule gives on Singapore trails
Naismith's 1892 rule allows an hour for every three miles plus an hour for every 2,000 feet of climb, and the day he sai...
Why stopping distance charts disagree at the same speed
At 90 km/h, Singapore's driving handbook says 95 metres, Britain's table gives 73 at a slightly higher speed, and US roa...
The 24 solar terms in 2026, and why the date moves every year
A solar term is a moment, not a day: 寒露 2026 is 8 October at 14:29. Here are all 24 with their times, matching the Hon...
When yi (一) and bu (不) change tone, and why pinyin usually doesn't show it
一 is said yí before a fourth tone and yì before the others; 不 becomes bú only before a fourth tone; and a third tone r...
Finding the years your lunar and solar birthdays fall on the same day
Your lunar birthday and your solar birthday meet only a few times in a lifetime. The first match is at 19 for 57% of peo...
How many ancestors did you have a thousand years ago?
Doubling every generation gives you about a trillion ancestors a thousand years back, more people than have ever lived....
Two published rules for the new moon disagree about one month in three
MABIMS and Muhammadiyah's wujudul hilal are both published and computable a year ahead. Worked through fourteen lunation...
A4 is the answer to an equation, and US Letter is not the answer to anything
Two constraints — a ratio of √2 and an area of one square metre — have exactly one solution, and that solution is A0. Th...
The octane numbers on American and Asian pumps are not the same scale
American 87 is roughly 91 RON, because the United States posts the average of two laboratory tests while most of the wor...
22.4 litres is only correct if you say at what pressure
A mole of ideal gas occupies 22.414 litres at one atmosphere and 22.711 litres at one bar, and NIST publishes both as se...
Fourteen elements have no single atomic weight
Carbon is printed as 12.011 on every wall chart. IUPAC does not publish a single figure for carbon, or for thirteen othe...
The standard behind your headphone warning advises against the warning
Your iPhone's 80 dB for 40 hours limit comes from ITU-T H.870, implementing WHO recommendations. That standard says dose...
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