proton boron 11 fusion / fission shielding

[Aero]

My Grandniece was born on March 3-rd. She weighed 7 jin, 4 tael. Things are not as confusing as they could be.

[blaisepascal]

Meters and yards are easy if you do not have to bee tooo precise with it.
A yard is roughly 1 meter (well 1 meter is 1.09 yards). So that is not so bad. I usually simply multiply meters by 3 to get a rough estimate in feet.
And to get pounds you multiply the kilograms by 2 (well 2.2 if you have to be more precise... 2 for the ladies ).
Inches... well as I said, most americans dont know how many inches go into a foot. They also can not tell me how many cubic inches make a gallon. These things are very, very simple in the metric system. 1 dm^3 is a liter. That is 10cmx10cmx10cm.
Also practical is that a litre of water roughly weighs (well actually has the mass of) 1kg. Water freezes at 0 degrees C and boils at 100 and so on...

40 inches to the meter is good too.

An a liter is a quart roughly.

I tend to use the 10ft = 3m estimate. It's good to less than 2%, which is close enough for the types of things I estimate. If I need better precision than 2in over 10ft (or 5cm over 3m), I can specify one system or the other.

For longer distances, I use the Golden Mean and fibonnaci numbers to get rough conversions between miles and km. As an example, 72mi = (55+13+2+1+1)mi, which roughly corresponds to (89+21+3+2+1)km = 116km. The actual conversion is 72mi=115.8722km, so it's close. This works because (a) the limit ratio of successive numbers in the Fibonnaci sequence is the golden mean, approximately 1.618, and (b) the conversion factor for miles to kilometers is 1.609. The two ratios are close enough for an estimate.

I had always been taught that a (US) gallon of water weighed 8lb. I was surprised to find out recently that it actually weighs closer to 8.33lb.

[Billy Catringer]

You can also use 1 km = 5/8 statute mile. That one is handy for me because I can usually do the math in my head. The nautical mile is 1.15 miles. I have to use a pencil and paper if I'm drunk or tired. The US gallon is 231 cubic inches. That got pounded into my head when I was working on some hydroponics systems. An Imperial gallon of water weighs 10lbs which, means that an Imperial gallon must be a hair over 277 cubic inches.

For the most part, the metric system is easier to cope with, I just wish that the metric gods would have set the meter and yard to equal lengths. That would have made switching over to the metric system far less painful for those of us who cannot roll their tongues up tight enough to speak French properly.

The foot and inch system is terribly convenient when you are working with furniture, jewelry boxes and those sort of things. I guess that is why some Japanese craftsman have hung onto the shaku and sun. The shaku is 11.95 inches and there are ten sun to the shaku.

[Skipjack]

The shaku is 11.95 inches and there are ten sun to the shaku.

The problem with that comparison is that there are 12 inches in the foot, not 10.

The kilogram was chosen because it was easier to make a reference of that. A gram is a very small amount. Back in the days it would have been to imprecise for larger weights. So it was easier to make a kilogram and divide that by 1000.

[Billy Catringer]

Which makes the sun about 1 1/8" long, I know. Too bad we didn't have sense enough to make the inch = 1/10 of a foot, huh?

[blaisepascal]

Bringing this moderately back on topic, MSimon's point that the sizes of the building/shielding/etc are likely to be in "English" measurements because the US construction industry works in "English" measures is a legitimate one. But even within that industry, the names of the sizes of goods is not completely within the measurement system. A standard 2"x4" board isn't 2" thick, nor 4" wide, but rather smaller. The same piece of lumber in Canada is called a 5x10, because it's nominally 5cmx10cm.

A lot of the dimensions used in the US construction trade are that way because of tradition and ease of getting material, not because there's anything inherently good about it.

Stick frame construction tends to have studs at 16" or 24" on center because those measurements evenly divide a standard 8'x4' sheet (8' divided by 6 is 16", divided by 4 is 24"). A slight change in the side of a standard sheet to 240cmx120cm would put equivalent studs at 40cm or 60cm spacing. That would perhaps be even easier to deal with than 16" or 24" as far as math, and the sheet would only be 1.5% shorter.

Alternatively you could make the standard sheet 250cmx125cm (2.5% longer), and get 5 studs on 50cm centers, and be even more "metricy".

Running a construction shop on the metric system wouldn't be any harder than running it on an "english" system -- if you could get the materials, especially sheet goods, sized in metric sizes. But there's no market incentive to change in the US right now.

[Skipjack]

Well historically that is clear. The imperial system is very old and was developed out of actual practical every day life situations. A foot really was a foot (I think it was later actually standardized to the length of the foot of some king). An ell was really the length of the lower arm bone "elle" and so on (if you have ever watched a sales person unroll and quickly guesstimate the length of a peace of fabric, you will emmediately know how that came to be).
Anyway, back then a dozen was a very popular number in trade and every day life.

[Skipjack]

Running a construction shop on the metric system wouldn't be any harder than running it on an "english" system

Well all the construction here in Europe is done in the metric system and I have not noticed that our construction is any worse than yours... In fact I know some construction people that worked overseas (in the US) and they would tell you that the way things are built in the US would not quite be legal here...

[tombo]

Keeping the units straight is the least of our minor engineering problems and yes it is a chore when our tables and handbooks have 3 kinds of metric in addition to several different disciplines worth of american units. Tons of refrigeration and gauges of wire anyone?
Having worked on mixed unit (metric/american) projects I discovered that it is better to design in inches and convert to mm for reasons of round off error and local material availability. For example yes I can get metric screws and shafting and steel shapes but it costs twice as much or more than inch designated ones. Also steel alloys are different on opposite sides of "the Pond" which to me was even more difficult to cope with. This is one of the perennial frictions between scientists and engineers and builders. When we get down to actual hardware some of us will straighten it out detail be detail as needed. Get over it. Learn to covert. It will stretch your mind.

[Skipjack]

I am converting it all the time. It just annoys me to no avail.
For all that dont want to do it in their heads, or can not do it in their heads, there is also
convertit.com
Awesome site! I love it.

[MSimon]

A lot of the dimensions used in the US construction trade are that way because of tradition and ease of getting material, not because there's anything inherently good about it.

Well no. A 2X4 is actually 2X4 rough cut. It is when it becomes finished lumber (faces planed) that the dimensions shrink.

That may not be strictly true these days but that is how it evolved.

[Art Carlson]

A lot of the dimensions used in the US construction trade are that way because of tradition and ease of getting material, not because there's anything inherently good about it.

Well no. A 2X4 is actually 2X4 rough cut. It is when it becomes finished lumber (faces planed) that the dimensions shrink.

That may not be strictly true these days but that is how it evolved.

My father, who worked in the lumber trade, claimed that 2X4s were originally rough cut to 2" by 4" and finished to 1-3/4" by 3-3/4". Once people got used to that being the meaning of 2X4, they started rough cutting them to 1-3/4" by 3-3/4" and finishing them to 1-1/2" by 3-1/2".

(Wikipedia tells the story differently, but I'm sticking by my Dad!)

[Billy Catringer]

A lot of the dimensions used in the US construction trade are that way because of tradition and ease of getting material, not because there's anything inherently good about it.

Well no. A 2X4 is actually 2X4 rough cut. It is when it becomes finished lumber (faces planed) that the dimensions shrink.

That may not be strictly true these days but that is how it evolved.

My father, who worked in the lumber trade, claimed that 2X4s were originally rough cut to 2" by 4" and finished to 1-3/4" by 3-3/4". Once people got used to that being the meaning of 2X4, they started rough cutting them to 1-3/4" by 3-3/4" and finishing them to 1-1/2" by 3-1/2".

(Wikipedia tells the story differently, but I'm sticking by my Dad!)

Your dad is right, Art. They've started shaving 2 x 6'x here. When I was a kid they were 1 1/2" x 5 1/2". I was at Lowes a few weeks ago buying some small lots of lumber and discovered that the 2 x 6's are now 1 1/2" x 5 1/4". Half inch plywood is now 15/32". I did not need any other sizes so I didn't check them, but you can bet that they have been shaved as well.

The older houses here, built just after WWI and earlier have 2" x X" lumber in them.

[olivier]

The imperial system is very old and was developed out of actual practical every day life situations.

Since it is not a physical unit I may be (even more) off topic, but my favorite unit is the British Guinea. I have been taught the inescapable logic by which it came to be worth twenty-one twentieths of a pound. I still believe something like that must have been invented by a psychopath.

A foot really was a foot...

All imperial units have their French equivalents which were in use before the Revolution. "An inch" translates as "un pouce" meaning "a thumb", "a foot" as "un pied" meaning "a foot", "a fathom" as "une brasse" meaning the distance you swim in one breaststroke movement. I let you discover how "yard" translates (a double entendre which may not be explained on a decent forum). Search on the excellent Québecois Grand Dictionnaire Terminologique to learn why there is some exaggeration there.

[chrismb]

Which is heavier - an ounce of feathers or an ounce of gold?

If you think you know that one, try;
which is heavier - a pound of feathers or a pound of gold?