a ? in regards to current si units

I think a meter was originally one pace of a ruler (king). Rather natural!! Why do you think a ruler is called a ruler?

A ruler is a person who governs, a rule is a guideline.

So, if you want company, take a ruler, if you want to measure, take a rule

Tony

In the SA English I know we measure with a ruler.

But I will accept, after all Oxford (with 1 000 007 words) is better than any local rule (expired school dictionary).

When I grew up the saying were "England waves the rules" or was it "rule the waves"?

I actually looked it up in the Pharos dictionary of my grandson :-

both ruler and rule are translated as "liniaal" "duimstok"

(inch-stick) which is your rule.

Interesting question, I don't know of any naturally occurring objects that could be used reliably as a standardized ruler, at least not any that are big enough to be practical, but there are some cheats you can use for approximations: A grown mans thumb is ~1" wide for example... here are a bunch of examples of 'anthropic' measurements: http://en.wikipedia.org/wiki/Cubit. I have measured many of mine and can tell you for example that my cubit is 18", my span is 9", my thumb is 1" wide at the knuckle... I use this knowledge to great effect and recommend anyone who deals with measurements should take some of themselves for future use.

If you only use a single anthropic unit (cubit, palm, span...) then you can build something using another persons same unit and you will get good results that are scaled to you... not quiet the same as what we think of as a ruler (as soon as you start adding sub-units things start to get really wacky), but pretty useful for deserted island applications none-the-less.

I gave you the wrong link for anthropic measurements... the correct link is:

http://en.wikipedia.org/wiki/Anthropic_units

The Newton is not a base unit! Anyway, good answer.

Perhaps not now... but on MY desert island the Newton is THE base unit. In fact it's the only unit. We do everything based on Newtons - you can even buy stuff with em. And I'm working on a giant Newton-powered death ray with which I'm going to destroy your puny candela powered world. Fools! Mwooahh ha ha ha! (damn, giving too much away again.)

but good point - thanks.

A Newton is the unit of force, and is defined as.........the force required to give a mass of 1kg at an acceleration of 1m/sec² Symbol N

f = m x g (N) f = force, m = mass, g = FORCE due to gravity, (9.81m/sec²)

May I ask what units use for force.

I hope that you are not confusing this with pressure or stress where the preferred unit is stupid.......the Pascal (Pa) which is defined as ...a force of 1N applied over an area of 1m² .......an incredibly small unit, it is more common to use MPa (Mega-Pascals) or 1N/mm² The bar or kg/cm² can also be used for pressure

Sure - Newtons are the unit of force, it's just (as SG80 reminded me) they are a derived unit, not a base unit.

That is, (as you just did) you can derive Newtons by using the base units of time, length and mass.

Base units can't be derived, they have to be defined, and the fewer base units you have the more powerful and universal your system becomes.

So the SI system has been pared down to seven base units, everything else (units of force, velocity, acceleration, pressure etc) may be defined in terms of them.

Oh shit!..........What was I thinking.

No!.................I was not thinking..........sorry for that error.

Yeah, well I did the same thing just up the page, so don't feel bad! And you were dead right about the stupid Pascal... never have to switch exponents so much as dealing with pressure.

Before thefrench revolution (1789) every seigneuries had the privilege to define their own measurement system. After the revolution, some lord heads in the basket and the abolition of privileges the young republic had to define a new measurement system. through the idealism of this period they look for a universal and eternal reference and they choose to define the meter as part of a earth meridian. So, two scientifics had in charge to really measure the distance between Dunkerque (north of France and Barcelona (north of spain) that took several years, one of them became fool, but the meter was defined and the metric system was born and is now adopted by all the countries .... except one or two...... and the NASA.

Comprehensive answer but I think we're missing the point here. All of this equipment is a far stretch from the pen & paper given to us in the question! And a lot of reference to Paris which I would mightily prefer to the desert island, but I need to build an airport first :-)

Basic astronomy will give us time and, ultimately also, distance.

Time will give us distance more portably if we use, as I suggested, a pendulum.

Distance will give us an accurate volume, which when filled with distilled water (boiled seawater) will give us a unit mass.

Force comes from mass, distance and time so again we are covered.

Force allows us to define the amp.

Temperature from the properties of aforementioned distilled water.

I remember a UK TV programme where they did just this; put boffins on a remote island and ask them to do some wonderful things with basic equipment, like make a map of the island. They had to invent ways to make ink, pen and paper, and make surveying instruments from tree-bark etc.

hey - no fair... sure I started with units that required lab equipment to measure, but pared it back to basic astronomy, fixed angles, distance, and even unit mass using volume of water based on distances. Maybe my post was too long winded to read through to the end.

On reflection mea culpa, I did read the whole post but then forgot your correct ending as I wrote mine as I was trying to wreck my brains thinking of the name of that programme .

And still can't.

I've been trying to think of other bases for length than astronomy e.g. parallel slits with sunlight, vibrations in a string, etc. I seem to remember the plague on Voyager Probe (or was it Pioneer) was designed by Carl Sagan and had a method to define a unit length, but again I think it was precision physics.

And by the way, I don't think as much as people drink I do.

What an elegant and interesting question. I'll give much greater thought to this tonight when meddlesome work does not intervene

My initial thought would be time. Or rather the measure of. Astronomical observation (from our own day to the transition of moons on planets) will give access to a universal clock. A simple Chinese water clock (i.e. drip, drip) would allow you to break the day into more useful units (sound familiar?), and from this a simple pendulum can swing in synch to give a standard length, viz:

T ≈ 2∏√(L/g)

Would I be right in saying that local variations in g due to height would be cancelled out by this method also??

I don't think you would cancel out variations in g by synchronising with the water clock (if that's what you meant), since both the pendulum and the water clock are dependent on g as their force. A droplet of water breaks off when the surface tension force is overcome by the weight force, and the weight force is m*g. So in very low gravity the droplet could be enormous by the time the forces were in equilibrium, and consequently the time between drips would be much greater. (Or maybe I misunderstood you). Nice idea though.

........Pi comes to mind..........

We could have 2Pi (radians).......or 360⁰

Oh!........What the hell.............just devise a new system of weights and measures.

http://en.wikipedia.org/wiki/Physical_constant

I remember in my physics class learning physics at a cc it drove me insane. Yet here i am on this site posting questions about something that has been bugging me .

The reason i asked the above question in base units and what is a natural unit has something to do with this really cool equation

1/x = 1-x to solve you must put in quadratic form

http://en.wikipedia.org/wiki/Golden_ratio

While reading about the golden ratio and how its related to the Fibonacci sequence and that the "Fine structure constant" has a ratio 1/137. I then wondered if there was some way of using it as a base measurement.

http://en.wikipedia.org/wiki/Fine-structure_constant

On following site it explains all the ways the golden ratio is expressed in several mathematical concepts.

http://goldennumber.net/math.htm

Somehow there is got to be a way to use this ratio or any of the known ratios in math such as pi,phi, sqrt of 2, sqrt 3 etc. as a kind of fixed universal and beyond type of measurement.

http://en.wikipedia.org/wiki/Mathematical_constant

I was thinking if you could get a fixed measurement from a geometric object that represents one of those ratios and derive and use as a measument reference.

I found this link, apparently i am not alone in my thinking
http://math.ucr.edu/home/baez/constants.html

here's other stuf

http://en.wikipedia.org/wiki/Natural_units
http://en.wikipedia.org/wiki/Fundamental_physical_constants

Ok.... you are in a desert island and you need to use a SI unit like a meter? Using only things you're finding on the island is not possible and only paper&pen is not enough! Measurement units are not mathematical entities but physical ones. The power of the SI units is that you don't need to go in Paris for the unit models, but in theory you can built the unit model in any lab with enough stuff... You are in a desert island and you need a measurement unit i.e. to measure the length? You are free to use everything you want... Just define the length unit as the length of your paper sheet, and the time unit as the time need to the pen to fall down from a height=paper length... and so on. The point is that a measurement unit is nothing of absolute or divine is just a convention between people. About the ratios (pi, golden ratio...) and use them as measurement unit I don't think that's possible... because they are ratios, they are adimensional entities: You can't use them to compare other physical entity.