Moonbear
Staff Emeritus
Gold Member
JasonRox said:
Note: I apologize for my attitude because I shouldn't be so rude, but sometimes I just have to let it out.
That's what happens when you forget to use your [rant] tags. It's okay to vent, just try to warn us when that's what you're doing.

Here's the silver lining in case you didn't know there was one. If you learn now how to find the right person to correct problems and learn how to talk to them persuasively so they really help you out, you've learned a valuable lesson in how to deal with people and get things done for when you're out in the working world, where you're going to run into even more incompetent people.

Sig figs are stupid, it's like interval estimation only far less reliable.

cepheid
Staff Emeritus
Gold Member
Norman said:
I know this is pedantic, but couldn't 20 be considered exact since there is no decimal place?
Not if "20" is a measurement that arose from some experiment etc. That's the whole point...you definitely don't know for sure that it is exactly 20...your instruments have some limited precision.

If, on the other hand, it is just the number 20, then fine.

btw...cronxeh...never heard of that convention that: '20' is one sig fig and '20.' is two sig figs. I always thought that '20' was just ambiguous. Never seen '20.' before. hmm...interesting.

Gza said:
I find the whole obsession with sig figs in introductory physics classes to be pretty stupid, IMHO.
Taking note of sig. figs. is something like brushing your teeth. A simple task which you can teach any adult. But getting that into HABIT is another matter, and should be taught from young.

But also, i sometimes tend to write all 12 digits from my calculator in any computation (esp. in physics) in all my workings because i find them easier to type than saving them in the memory bank of the calculator. But of course, answers are in the appropriate amt. of sig figs.

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cronxeh
Gold Member
cepheid said:
Not if "20" is a measurement that arose from some experiment etc. That's the whole point...you definitely don't know for sure that it is exactly 20...your instruments have some limited precision.

If, on the other hand, it is just the number 20, then fine.

btw...cronxeh...never heard of that convention that: '20' is one sig fig and '20.' is two sig figs. I always thought that '20' was just ambiguous. Never seen '20.' before. hmm...interesting.

True but it brings home the point

It could be 20.1 or 20.2 or 20.3 or 20.4 or it could be 19.5 or 19.6 or 19.7 or 19.8 or 19.9 - all rounded from some other calculation, or even worse - by a program that student writes. Then there is a problem - we cant say if its 19.5 or 20.4 - it just says '20' and not '20.'

BLUE_CHIP
Moonbear said:
How would they know if you used a fountain pen? As far as I can tell, fountain pen ink and roller ball ink and gel pen ink all look pretty much the same on paper. Then again, I have a nice calligraphy pen I can loan you...the kind with a nub on the end and you have to keep dipping in ink. Makes for fun blobs and smears to prove you're following the rules. :rofl:
After having done his MSci. in maths, he went on a 2 year calligraphy course........ HE KNOWS when you dont follow the creiteria

Ill see if i can get a picture :P

Also, the number of sigfigs depends on the given tolerance. 20m/s^2 could be one or two (or more sigfigs)...

(20 +/- 10)m/s^2 is 1 sigfig, since the zero only tells you the magnitude of the number and only the first digit contains "relevant data" about the measurement
(20 +/- 1)m/s^2 is 2 sigfigs, since the outcome of the measurement is indicated by both digits, so you need to keep track of both in calculations

- Kamataat

Non-recycled paper
wow. my physics teacher is the best environmentalist I've ever seen. He will not let you in his classroom with a disposable cup or disposable anything; he insists it has to be reusable so fewer trees are used. Also, to decrease the number of trees that have to be used to make paper, he makes us e-mail our homework. The only time we use paper in his class is for notes (in which case we must use both sides of paper) which are two or 3 pages long and quizes and tests.

ShawnD
Your environmentalist teacher is insane. Trees, like corn, are grown on farms. If you need more trees, you simply grow more. Wasting lots of paper is like throwing out a whole ear of corn, of course it's bad, but forcing students to always use both sides is as crazy as eating the corn cob.
Sorry but I had corn on the cob for supper

As for a number like 100, I would interpret that as 3 digits. The general rule is that everything is done for a reason. If you write 5.00, it's because just 5 is not the same. If you write 100, it's because 1x10^2 is not the same.

DaveC426913
Gold Member
ShawnD said:
Your environmentalist teacher is insane. Trees, like corn, are grown on farms. If you need more trees, you simply grow more.
Yes, Shawn D is correct. If you need more paper, you just use more land, more equipment, more bleach for processing the paper, dump more toxic byproducts in the water, creating higher banks of foam (ever been within ten miles of a paper mill?) and create more waste heat and toxic gasses.

And when all that runs out - well, they're finding new planets every day!

As for a number like 100, I would interpret that as 3 digits. The general rule is that everything is done for a reason. If you write 5.00, it's because just 5 is not the same. If you write 100, it's because 1x10^2 is not the same.
Yeah, I think that's how most things are handled in the science of mathematics: it's all a matter of interpretation - you know, common sense.

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ShawnD
DaveC426913 said:
Yes, Shawn D is correct. If you need more paper, you just use more land, more equipment, more bleach for processing the paper, dump more toxic byproducts in the water, creating higher banks of foam (ever been within ten miles of a paper mill?) and create more waste heat and toxic gasses.
Break it down this way

Recycling
-Transport paper to some recycling place
-Grind the paper
-Bleach the paper
-Remake the paper
-Transport to stores

Environmental Impact:
-Roughly the same amount of bleeching as new paper

Landfill old stuff, make new stuff
-Transport trees to some place
-Grind the trees
-Bleach the pulp
-Make the paper
-Transport to stores

Environmental Impact:
-Landfilled paper is eaten by bacteria to create methane gas which heats peoples' homes

The only common recycling process that actually saves energy is recycling aluminum cans. Aluminum from bauxite takes much more energy than recycled aluminum.
Paper, however, is the exact opposite. Recycling paper requires energy every step of the way. Landfilling paper actually has a net gain in energy since you get a similar amount of energy from the collected methane as you would if you just burned the trees in the first place; being able to use the trees as paper before collecting the energy is just an added bonus.
Plastic is another thing that requires more energy to recycle than to make new, but plastic doesn't naturally break down so I would say that's totally worth recycling.

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Imparcticle said:
The only time we use paper in his class is for notes (in which case we must use both sides of paper) which are two or 3 pages long and quizes and tests.
Hahaha! I would do so well in that class! All my notes are highly compressed due to my extremely small handwriting. https://www.physicsforums.com/archive/t-15640_Tiny_Notetaking.html

I even have a more recent example with my AP Government notes, but id rather not get into that.

So far my personal record is 9 of my lines per 1 college ruled line, according to your teacher then id definitely be saving paper and the environment.

Motai: My teacher'd love you!! You know, our quizes are really short, usually 5 questions (and 7 points each...) long. My teacher gives it to us in slips of paper, so that paper can be saved. But we end up having to use our own paper to do the problems on, so this could be his way of saving money. :rofl:

Your environmentalist teacher is insane. Trees, like corn, are grown on farms. If you need more trees, you simply grow more. Wasting lots of paper is like throwing out a whole ear of corn, of course it's bad, but forcing students to always use both sides is as crazy as eating the corn cob.
Sorry but I had corn on the cob for supper

lol. Very true. I think I'll tell him that. I'll come back and tell you his reply.

I have to e-mail my hmwk now....

Chi Meson
Homework Helper
ShawnD,
What's your take on "resource recovery" , that is, places that burn trash for electricity? I have a similar attitude as yours when it comes to recycling, and I've thought that burning the plastic bags to get electricity is probably the best use of the resource if the gaseous output is "not too toxic."

That last point, depending on who you talk to, varies greatly. Our own "RR" plant in Connecticut is much cleaner than our coal-fired plants (but our "sooty six" are particularly bad).

ShawnD
Chi Meson said:
ShawnD,
What's your take on "resource recovery" , that is, places that burn trash for electricity?
I support them all the way. Most hydrocarbons burn fairly clean when given enough oxygen.

Chi Meson