• May 31, 2016
May 31, 2016, 3:59:48 pm *
Welcome, Guest. Please Log In to participate in forums.
News: Talk online about your experiences as an adjunct, visiting assistant professor, postdoc, or other contract faculty member.
 
Pages: 1 ... 337 338 [339] 340 341 ... 931
  Print  
Author Topic: Bang Your Head on Your Desk - the thread of teaching despair!  (Read 2424107 times)
genius_at_large
Wylie E. Coyote, Genius at Large
Distinguished Senior Member
*****
Posts: 2,213


« Reply #5070 on: March 22, 2012, 4:40:11 pm »

Patron Saint of the Snowflakes has missed a third class now (unexcused) in a class that only meets once a week. When he does show up, he insists on behaving as if he's still in middle school. Looks like we'll be able free up some more scholarship money for next semester if he doesn't shape up fast.
Logged

I'm just a peckerwood who lives in the hills with too many guns.

I don't get lost-I like to investigate alternative destinations.
mystictechgal
Happy in my "full, rich adulthood", and as a
Member-Moderator
Distinguished Senior Member
*****
Posts: 18,668

One step at a time


« Reply #5071 on: March 23, 2012, 12:28:02 am »

And if the learner intended recipient of said knowledge is not engaged, it's OUR fault. We didn't inspire/motivate/captivate/entertain/stimulate them enough.

You don't sound learner-centered, my embittered amigo. You may require some professional indoctrination development training.

Do we work at the same place?

As for all the sigfig talk, I too am having trouble explaining the difference between 100 g and 100.0 g.  We should not be having these issues this far into the semester.  Haven't we been applying these rules all term?  (Well, some of us have.)

"We" (I put it in quotes because sometimes it feels like the only part of "we" that's listening is "me") have a big discussion about the balance and about how one should always write the mass to three decimals because our balances read to the nearest milligram and...

<insert loud, scary, thunderous voice>

THOU SHALT NOT ROUND DATA!

If the mass is 50.000 g then you dang well better write 50.000 g. I'll repeat-

<insert loud, scary, thunderous voice>

THOU SHALT NOT ROUND DATA!

Most students get it but I still have a few in the last half of the term who struggle with how to write the mass and how many decimals to use when subtracting masses (say, final mass - initial mass). These students, the ones who struggle with how to record masses as read from the balance, usually are doing very poorly, overall, in the course.

Alan

Interesting. Our scales go to three decimals, too, but I've lost points for using them. Many of the directions for labs specify the use of tenths or hundredths, which we then round to, and regardless of how specific our measuring techniques might be the final answer contains no more figures than the least of any of the numbers used in the calculation. That's sometimes problematic when working end of chapter problems when, for instance, the fewest figures used in one of the givens is two, I get an answer of, say, 0.0654 and convert it, as taught, to 6.4 x 10^-2 only to find that the answer given in the back of the book is 0.0654.
Logged

Quote
You must realize that a university cannot educate you. You must do that for yourself, although a college or university is the place where it is likely that you can study most efficiently.
http://www.lhup.edu/~dsimanek/chapman.htm

"Is all the same, only different" -- HL
cc_alan
is a wossname
Distinguished Senior Member
*****
Posts: 10,259

Caution! Nekkid Zamboni driver ahead.


« Reply #5072 on: March 23, 2012, 1:30:15 am »

Interesting. Our scales go to three decimals, too, but I've lost points for using them. Many of the directions for labs specify the use of tenths or hundredths, which we then round to, and regardless of how specific our measuring techniques might be the final answer contains no more figures than the least of any of the numbers used in the calculation. That's sometimes problematic when working end of chapter problems when, for instance, the fewest figures used in one of the givens is two, I get an answer of, say, 0.0654 and convert it, as taught, to 6.4 x 10^-2 only to find that the answer given in the back of the book is 0.0654.

The bolded part sounds like a simple incompatibility between the instructions and the equipment. Are you using a publisher's lab manual or are you using a "home-brew" lab manual? In one of the labs I teach we use a publisher's lab manual and I make a few corrections/additions to the instructions at the start of each lab to reconcile the differences between our lab's equipment and that assumed by the lab manual.

I obviously don't know your lab setup but I'm scratching my head as to why you would lose credit for properly recording a mass from the balance. It's possible that the difference is coming from a later calculation. Have you asked your lab instructor about it? If you've lost credit for simply recording a balance reading to 3 decimals, I suggest asking your lab instructor to explain. If it's "because that's what the instructions say" then you could push it or write it in your evaluation of the lab instructor. I guarantee that if an evaluation came back where I work with a reasoned description as to how the lab instructor is following incorrect lab manual instructions just "because", the chair would at least inquire about it.

I've had that battle with an instructor when it came to incorrect information in the textbook. This coworker would use something incorrect from the book even though that person knew it was wrong. When I asked for the reason, it was something along the lines of "not wanting to confuse the students by telling them something different."

<insert head-banging moment>

As for the calculation differences, this could be due to any number of reasons-

1. The answer in the book is wrong.
2. You are confusing the significant figure rules for addition/subtraction with multiplication/division.

As to my reason #2 and using your answer-

0.0654 has three significant figures as written but four decimal places. 0.065 or 6.5x10^-2 has three decimals but 2 significant figures. If the final answer is supposed to have three decimals then 0.065 is correct (say, the addition/subtraction rule). If the final answer is supposed to have three significant figures then 0.0654 is correct.

Alan
Logged

Guess what? I got a fever and the only prescription is MORE COWBELL!
conjugate
Compulsive punster and insatiable reader, and
Member-Moderator
Distinguished Senior Member
*****
Posts: 19,152

Tends to have warped sense of humor


« Reply #5073 on: March 23, 2012, 10:49:14 am »


I obviously don't know your lab setup but I'm scratching my head as to why you would lose credit for properly recording a mass from the balance. It's possible that the difference is coming from a later calculation. Have you asked your lab instructor about it? If you've lost credit for simply recording a balance reading to 3 decimals, I suggest asking your lab instructor to explain. If it's "because that's what the instructions say" then you could push it or write it in your evaluation of the lab instructor. I guarantee that if an evaluation came back where I work with a reasoned description as to how the lab instructor is following incorrect lab manual instructions just "because", the chair would at least inquire about it.


If some other numbers involved in the computation are available only to one or two significant figures, then possibly the lesson being taught is that all the numbers involved should have about the same level of precision.

Suppose I measure, say, the radius of a circle to the nearest cm, and use an approximation of pi to (say) 5000 digits to compute the circumference or area.  Obviously, I can't expect 5000 digits of precision in the result.  It may be that the lab instructor is trying to emphasize this by counting off for students who use higher precision in one measurement than is available in another measurement.

Mind you, it sounds pretty silly to me, but then I don't deal with numbers that represent reality in any sense.  I only rarely tell my students to write "units" or "square units" after problems that involve finding lengths or areas when units aren't specified, because I don't think in those terms much myself.
Logged

Unfortunately, I think conjugate gives good advice.
∀ε>0∃δ>0∋|xa|<δ⇒|(x)-(a)|<ε
cc_alan
is a wossname
Distinguished Senior Member
*****
Posts: 10,259

Caution! Nekkid Zamboni driver ahead.


« Reply #5074 on: March 23, 2012, 11:08:46 am »


I obviously don't know your lab setup but I'm scratching my head as to why you would lose credit for properly recording a mass from the balance. It's possible that the difference is coming from a later calculation. Have you asked your lab instructor about it? If you've lost credit for simply recording a balance reading to 3 decimals, I suggest asking your lab instructor to explain. If it's "because that's what the instructions say" then you could push it or write it in your evaluation of the lab instructor. I guarantee that if an evaluation came back where I work with a reasoned description as to how the lab instructor is following incorrect lab manual instructions just "because", the chair would at least inquire about it.


If some other numbers involved in the computation are available only to one or two significant figures, then possibly the lesson being taught is that all the numbers involved should have about the same level of precision.

But that question is whether it's a measurement or a computation. If someone is writing down a mass measurement and the balance reads to 1, 2, or 3 decimals, then regardless of what the instructions say the mass measurement needs to be written according to the instrument. Otherwise you've lost the ability to recover your original data.

*Data* is not rounded.

Alan
Logged

Guess what? I got a fever and the only prescription is MORE COWBELL!
octoprof
Member-Moderator
Distinguished Senior Member
*****
Posts: 49,600

Love your loved ones while you can.


WWW
« Reply #5075 on: March 23, 2012, 11:17:39 am »

But that question is whether it's a measurement or a computation. If someone is writing down a mass measurement and the balance reads to 1, 2, or 3 decimals, then regardless of what the instructions say the mass measurement needs to be written according to the instrument. Otherwise you've lost the ability to recover your original data.

*Data* is not rounded.

Alan

I love this post. I can't seem to get my cost accounting students to understand that all that crazy rounding they do results in very inaccurate numbers. And, those numbers are meant to be used to make decisions. So, maybe, having more accurate results, might be a good idea, eh? 

They seem to think calculations of costs should only have two decimal places because they are dollars...

<bangs head on desk>
Logged

Love your neighbor.

Your new cephaloverlord.
ALL HAIL TO THE OCTO!!!

When you are accustomed to privilege, equality feels like oppression.
cc_alan
is a wossname
Distinguished Senior Member
*****
Posts: 10,259

Caution! Nekkid Zamboni driver ahead.


« Reply #5076 on: March 23, 2012, 11:22:50 am »

But that question is whether it's a measurement or a computation. If someone is writing down a mass measurement and the balance reads to 1, 2, or 3 decimals, then regardless of what the instructions say the mass measurement needs to be written according to the instrument. Otherwise you've lost the ability to recover your original data.

*Data* is not rounded.

Alan

I love this post. I can't seem to get my cost accounting students to understand that all that crazy rounding they do results in very inaccurate numbers. And, those numbers are meant to be used to make decisions. So, maybe, having more accurate results, might be a good idea, eh? 

They seem to think calculations of costs should only have two decimal places because they are dollars...

<bangs head on desk>

Office Space! Siphon-off those "unneeded" decimal places and let's party!

<insert more exclamation points>

Alan
Logged

Guess what? I got a fever and the only prescription is MORE COWBELL!
octoprof
Member-Moderator
Distinguished Senior Member
*****
Posts: 49,600

Love your loved ones while you can.


WWW
« Reply #5077 on: March 23, 2012, 11:24:50 am »

But that question is whether it's a measurement or a computation. If someone is writing down a mass measurement and the balance reads to 1, 2, or 3 decimals, then regardless of what the instructions say the mass measurement needs to be written according to the instrument. Otherwise you've lost the ability to recover your original data.

*Data* is not rounded.

Alan

I love this post. I can't seem to get my cost accounting students to understand that all that crazy rounding they do results in very inaccurate numbers. And, those numbers are meant to be used to make decisions. So, maybe, having more accurate results, might be a good idea, eh? 

They seem to think calculations of costs should only have two decimal places because they are dollars...

<bangs head on desk>

Office Space! Siphon-off those "unneeded" decimal places and let's party!

<insert more exclamation points>

Alan

<cackles!>

They just can't get that when you round off those "unneeded" decimal places and then multiple that cost-per-unit by 2,000,000 units... the results are pretty much crap.
Logged

Love your neighbor.

Your new cephaloverlord.
ALL HAIL TO THE OCTO!!!

When you are accustomed to privilege, equality feels like oppression.
galactic_hedgehog
Procrastinating, Python-quoting, Blue Blazer-drinking, chocolate-chip cookie-eating, Pastafarian, Not So
Distinguished Senior Member
*****
Posts: 18,841

Mind Ninja


WWW
« Reply #5078 on: March 23, 2012, 11:36:50 am »

Interesting. Our scales go to three decimals, too, but I've lost points for using them. Many of the directions for labs specify the use of tenths or hundredths, which we then round to, and regardless of how specific our measuring techniques might be the final answer contains no more figures than the least of any of the numbers used in the calculation. That's sometimes problematic when working end of chapter problems when, for instance, the fewest figures used in one of the givens is two, I get an answer of, say, 0.0654 and convert it, as taught, to 6.4 x 10^-2 only to find that the answer given in the back of the book is 0.0654.

The bolded part sounds like a simple incompatibility between the instructions and the equipment. Are you using a publisher's lab manual or are you using a "home-brew" lab manual? In one of the labs I teach we use a publisher's lab manual and I make a few corrections/additions to the instructions at the start of each lab to reconcile the differences between our lab's equipment and that assumed by the lab manual.

I obviously don't know your lab setup but I'm scratching my head as to why you would lose credit for properly recording a mass from the balance. It's possible that the difference is coming from a later calculation. Have you asked your lab instructor about it? If you've lost credit for simply recording a balance reading to 3 decimals, I suggest asking your lab instructor to explain. If it's "because that's what the instructions say" then you could push it or write it in your evaluation of the lab instructor. I guarantee that if an evaluation came back where I work with a reasoned description as to how the lab instructor is following incorrect lab manual instructions just "because", the chair would at least inquire about it.

It could also be due to an instructor who doesn't know the proper rules of rounding.  Perhaps that person thinks that you round all number to, say, two digits before calculations, instead of after.
Logged

ellaminnowphd
Curiously Strong
Distinguished Senior Member
*****
Posts: 3,810


« Reply #5079 on: March 23, 2012, 11:47:12 am »

Apparently when I was in elementary school (I don't remember this, it's my mom's story) I told my teacher that what was wrong with the world was that everyone rounded up.  My teacher was amused enough to call my mom. 
Logged

cc_alan
is a wossname
Distinguished Senior Member
*****
Posts: 10,259

Caution! Nekkid Zamboni driver ahead.


« Reply #5080 on: March 23, 2012, 11:52:17 am »

Interesting. Our scales go to three decimals, too, but I've lost points for using them. Many of the directions for labs specify the use of tenths or hundredths, which we then round to, and regardless of how specific our measuring techniques might be the final answer contains no more figures than the least of any of the numbers used in the calculation. That's sometimes problematic when working end of chapter problems when, for instance, the fewest figures used in one of the givens is two, I get an answer of, say, 0.0654 and convert it, as taught, to 6.4 x 10^-2 only to find that the answer given in the back of the book is 0.0654.

The bolded part sounds like a simple incompatibility between the instructions and the equipment. Are you using a publisher's lab manual or are you using a "home-brew" lab manual? In one of the labs I teach we use a publisher's lab manual and I make a few corrections/additions to the instructions at the start of each lab to reconcile the differences between our lab's equipment and that assumed by the lab manual.

I obviously don't know your lab setup but I'm scratching my head as to why you would lose credit for properly recording a mass from the balance. It's possible that the difference is coming from a later calculation. Have you asked your lab instructor about it? If you've lost credit for simply recording a balance reading to 3 decimals, I suggest asking your lab instructor to explain. If it's "because that's what the instructions say" then you could push it or write it in your evaluation of the lab instructor. I guarantee that if an evaluation came back where I work with a reasoned description as to how the lab instructor is following incorrect lab manual instructions just "because", the chair would at least inquire about it.

It could also be due to an instructor who doesn't know the proper rules of rounding.  Perhaps that person thinks that you round all number to, say, two digits before calculations, instead of after.

Oh, yes. That's a good thought. Well, not a "good" thought but... you know. I have students who make that mistake.

<off to party with Octo on our new island that we just bought with all those "unneeded" decimal places>

Hmm. Where did I put my extra flare?

Alan
Logged

Guess what? I got a fever and the only prescription is MORE COWBELL!
octoprof
Member-Moderator
Distinguished Senior Member
*****
Posts: 49,600

Love your loved ones while you can.


WWW
« Reply #5081 on: March 23, 2012, 12:20:55 pm »

Interesting. Our scales go to three decimals, too, but I've lost points for using them. Many of the directions for labs specify the use of tenths or hundredths, which we then round to, and regardless of how specific our measuring techniques might be the final answer contains no more figures than the least of any of the numbers used in the calculation. That's sometimes problematic when working end of chapter problems when, for instance, the fewest figures used in one of the givens is two, I get an answer of, say, 0.0654 and convert it, as taught, to 6.4 x 10^-2 only to find that the answer given in the back of the book is 0.0654.

The bolded part sounds like a simple incompatibility between the instructions and the equipment. Are you using a publisher's lab manual or are you using a "home-brew" lab manual? In one of the labs I teach we use a publisher's lab manual and I make a few corrections/additions to the instructions at the start of each lab to reconcile the differences between our lab's equipment and that assumed by the lab manual.

I obviously don't know your lab setup but I'm scratching my head as to why you would lose credit for properly recording a mass from the balance. It's possible that the difference is coming from a later calculation. Have you asked your lab instructor about it? If you've lost credit for simply recording a balance reading to 3 decimals, I suggest asking your lab instructor to explain. If it's "because that's what the instructions say" then you could push it or write it in your evaluation of the lab instructor. I guarantee that if an evaluation came back where I work with a reasoned description as to how the lab instructor is following incorrect lab manual instructions just "because", the chair would at least inquire about it.

It could also be due to an instructor who doesn't know the proper rules of rounding.  Perhaps that person thinks that you round all number to, say, two digits before calculations, instead of after.

Oh, yes. That's a good thought. Well, not a "good" thought but... you know. I have students who make that mistake.

<off to party with Octo on our new island that we just bought with all those "unneeded" decimal places>

Hmm. Where did I put my extra flare?

Alan

Those unneeded decimal places are the explanation for a classic financial fraud in banks...

<fires up the grill for some ribeyes>
« Last Edit: March 23, 2012, 12:21:30 pm by octoprof » Logged

Love your neighbor.

Your new cephaloverlord.
ALL HAIL TO THE OCTO!!!

When you are accustomed to privilege, equality feels like oppression.
conjugate
Compulsive punster and insatiable reader, and
Member-Moderator
Distinguished Senior Member
*****
Posts: 19,152

Tends to have warped sense of humor


« Reply #5082 on: March 23, 2012, 12:35:46 pm »


Those unneeded decimal places are the explanation for a classic financial fraud in banks...

<fires up the grill for some ribeyes>

Also, a key plot element of the second Superman movie, when Richard Pryor played the role of the programmer who first conceived the scheme.

In addition (warning: programming trivia to follow) because many personal computers early on did not use floating-point chips, money was often stored as whole numbers (integers) through the clever scheme of multiplying by 100.  After the "round-off" scheme became known, many banks required that calculations keep (I think) down to the nearest thousandth of a cent, or something silly, so that integer money had to be (dollars times one hundred thousand).  Since there were limits on the size of whole numbers (older PCs could not handle integers bigger than about 4.29 billion), larger number quantities necessarily required some fractions be dropped.  Thus, some software had to be specially written to enable calculations involving many millions of dollars accurate to a thousandth of a cent, to prevent the error that happens when you give a computer too big a number to cope with.

In particular, some versions of BASIC had a special "money" type so as to allow these kinds of calculations.  Today, many programming languages allow arbitrary precision calculations by specially programming in how to add, multiply, etc. numbers bigger than the maximum "built-in" number size, so this is less of a problem.

My moan of despair for today:

Today was a very important lecture.  It introduced the basic concepts of an idea that we will spend the next two or three weeks (at least) studying.  It's too bad for the several students (almost half the class) who weren't here today, because I'm sure not going to review especially for them.  "Get the notes from one of your classmates," I will say, and it's not my problem if the notes and the book together don't help them understand what an infinite series is.

Logged

Unfortunately, I think conjugate gives good advice.
∀ε>0∃δ>0∋|xa|<δ⇒|(x)-(a)|<ε
cc_alan
is a wossname
Distinguished Senior Member
*****
Posts: 10,259

Caution! Nekkid Zamboni driver ahead.


« Reply #5083 on: March 23, 2012, 12:42:19 pm »

Cool!

(Not for the despair but for the other information)

Alan
Logged

Guess what? I got a fever and the only prescription is MORE COWBELL!
mystictechgal
Happy in my "full, rich adulthood", and as a
Member-Moderator
Distinguished Senior Member
*****
Posts: 18,668

One step at a time


« Reply #5084 on: March 23, 2012, 12:43:05 pm »


I obviously don't know your lab setup but I'm scratching my head as to why you would lose credit for properly recording a mass from the balance. It's possible that the difference is coming from a later calculation. Have you asked your lab instructor about it? If you've lost credit for simply recording a balance reading to 3 decimals, I suggest asking your lab instructor to explain. If it's "because that's what the instructions say" then you could push it or write it in your evaluation of the lab instructor. I guarantee that if an evaluation came back where I work with a reasoned description as to how the lab instructor is following incorrect lab manual instructions just "because", the chair would at least inquire about it.


If some other numbers involved in the computation are available only to one or two significant figures, then possibly the lesson being taught is that all the numbers involved should have about the same level of precision.

Suppose I measure, say, the radius of a circle to the nearest cm, and use an approximation of pi to (say) 5000 digits to compute the circumference or area.  Obviously, I can't expect 5000 digits of precision in the result.  It may be that the lab instructor is trying to emphasize this by counting off for students who use higher precision in one measurement than is available in another measurement.

Mind you, it sounds pretty silly to me, but then I don't deal with numbers that represent reality in any sense.  I only rarely tell my students to write "units" or "square units" after problems that involve finding lengths or areas when units aren't specified, because I don't think in those terms much myself.


Yes. If one of the given numbers used in the computation only has 2 sig figs then the final answer should only have 2 sig figs.

And, yes, they're labs from the lab manual that often specify rounding of the scale/temperature/spectrographic/etc. data. Much of the time I ignore that--at least when taking my readings, if not when reporting them. (I am mindful of admonitions here, and in class, to pay attention to the directions.) I will, though, often round off intermediate calculations to 3 or 4 decimals, since that's how many decimals my professor's calculator seems to provide. The variation in calculators in the class sometimes provokes some discussion, but after the first couple of weeks the prof usually figures out who has, generally, what kind of calculator and if we're close and it's an obvious difference in rounding it's acceptable. I still don't like it when I round actual readings of data, though, I'm too OCD to like it--but, I do it.

My profs know the rounding rules. Sometimes, to make it a bit easier on us I've had them explain that in XYZ case (although I can't think of an example right now) the formal rules say to do ABC if one thing applies and DEF if something else is true, but, for now, we should just stick to the rules we know.

It's getting easier, but I'll still sometimes forget to apply the correct rule if, say, we've added numbers and then used that result later in the string of calculations to multiply, particularly when we've only done one of the operations early on and everything after has been a different operation. I tend to use the rule for whatever I've done last, which sometimes isn't the correct rule to apply. I'm learning.
Logged

Quote
You must realize that a university cannot educate you. You must do that for yourself, although a college or university is the place where it is likely that you can study most efficiently.
http://www.lhup.edu/~dsimanek/chapman.htm

"Is all the same, only different" -- HL
Pages: 1 ... 337 338 [339] 340 341 ... 931
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.9 | SMF © 2006-2008, Simple Machines LLC Valid XHTML 1.0! Valid CSS!
  • 1255 Twenty-Third St., N.W.
  • Washington, D.C. 20037
subscribe today

Get the insight you need for success in academe.