Quiz: Firkins, hides and metres
How much, how long, how hot...
Wednesday marks the 50th anniversary of the SI system of units - better known as the modern metric system. Defining units, though, is no simple task - as this quiz will show....
1.) On the unity of units
Some of the SI units are familiar: the metre, kilogram, second. In October 1960, there were three others. What were they?
- ohm, joule, watt
- volt, celsius, lumen
- ampere, kelvin, candela
- firkin, pennyweight, jiffy
2.) Who counted those?
A seventh unit was later added, in 1971: the mole. What was it?
- the number of atoms in 12 grams of carbon
- the number of photons in one watt of light
- the number of metres from the Earth to the Moon
- the number, in cords, that a woodchuck could chuck if it could, in fact, chuck wood
3.) Turn up the volume
The SI system defined all the basic units, from which other units could be derived. A litre, for instance, is 10cm x 10cm x 10cm - and is how many pints?
4.) A long time ago - but how long?
The metre supplanted an untold number of archaic and irreconcilable measures of length. Which of these is NOT a former length measure?
5.) Forcing the issue
In 1998 Nasa lost a $125m Mars orbiter because its software was working in pounds-force, while the hardware was programmed in the SI unit for force, which is...
6.) Measuring candle power
The candela was first based on a candle made using * fat.
7.) In league with an author
Jules Verne popularised a unit of length with "20,000 Leagues Under the Sea". But how many kilometres is that?
- About 100,000
- About 1,000,000
- About 1,000,000,000
8.) Weighty question
Which of these weighs the most?
- 84 pounds
- 6 stone
- 3 quarters (or tods)
- they are all the same
9.) How low can you go?
Kelvin was the agreed SI temperature scale. Which most accurately describes the zero on this scale (or "absolute zero")?
- temperature at which atoms stop moving
- point at which liquid hydrogen freezes
- the lowest attainable temperature of an ice/water/salt mix
- In addition, the ampere (to measure electric current), kelvin (temperature) and candela (luminous intensity) were formalised. The others can be derived from these fundamental units, except the firkin (a quarter of a barrel, 40.9 litres), the pennyweight (1/20 of a troy ounce, or 1.56 grams) and the jiffy (two shakes of a lamb's tail).
- A mole is the number of individual atoms in exactly 12 grams of the most common form of carbon. And how many is that? A shade over 602,214,179,000,000,000,000,000.
- One pint is 568 millilitres, and a litre is 1.76 pints.
- A hide was actually a hotly disputed unit of area of around 120 acres (ahem, 49 hectares). A pace was a Roman's full stride (about a metre and a half), a barleycorn was a third of an inch (8.5 millimetres) and a chain 22 yards (about 20 metres and incidentally the distance between the stumps in cricket).
- The newton is the SI unit of force - it's the push needed to get a kilogram going one metre per second faster, every second.
- It was whale fat. More formally, a candela is the intensity of a source that puts out yellow light at 1/683 watt per steradian of solid angle. Aren't you glad they worked that out?
- It would have been 100,000 km. A league was originally the distance one could walk in an hour - the title refers to an underwater journey equivalent to about two and a half times around the Earth.
- They're all equal, and all based on the pound, with 14 pounds in a stone and 28 pounds in a quarter (it's a quarter of a "hundredweight" which is in turn 1/20 of an Imperial ton). The tod was the same 28-pound measure, used specifically for wool. See why one agreed unit is a good thing?
- Like the speed of light, absolute zero - where even the tiniest atomic motion freezes solid - can never really be reached, although scientists can get incredibly close. Zero on the Fahrenheit scale was defined as the ice/salt/water mix, and hydrogen freezes at a cool minus 259C, or 14 kelvin.
0 - 3 : it hertz to say
4 - 6 : parsec for the course
7 - 9 : treat yourself to a dram
Pictures courtesy National Physical Laboratory, Science Photo Library, Thinkstock