ATTN: Christophera re: Common Sense

[The Almond]

In an attempt not to derail the nearly 200 page behemoth thread you're participating in, I'm starting a new thread about common sense. You're appealing to common sense in almost every post in the thread, and I'd like to test your common sense at evaluating quantitative scientific outcomes.

For each of these questions, provide your common sense, non-math based answer:

1) Structural Engineering

a) What loading per square length unit should be employed for office spaces in calculations for live load?

b) Which will produce greater deflection on a cantilevered rectangular beam: A single point load at the end of the beam, or a distributed load equal to half of the point load over the entire beam?

2) Physics

a) Which object has greater kenetic energy, a bowling ball weighing 5kg and travelling at 1/3rd the speed of light, or a freight train weighing 500,000Gg (giga grams) travelling at 50km/hr?

b) Which is hotter: the surface of the sun, the core of the sun or the area immediately around the sun?

c) How far away does an object have to be in air from an object radiating heat at 500 KJ/hr to prevent the nominal temperature rise in aluminum from being greater than 200 K after 5 minutes?

3) Materials Science

a) Will concrete harden under water?

b) Will cold water always freeze faster than hot water?

c) Which metal is stiffer (i.e. will have lower deflection given constant load, length and moment of intertia): Cast iron (ASTM 20), Wrought Aluminum 6061-T6, or Magnesium alloy AM 1004-T61?

4) Chemistry

a) What has a higher pH, 0.5M Sulfuric Acid or 18M Hydrocyanic Acid?

b) Which takes up more space, 1 Mol of Hydrogen Gas or 1 Mol of Radon at constant temperature?

c) Is Iron more likely to rust at higher pH or lower pH?


Ok, that's 11 questions for you to ponder. I suppose you could look up the answers to all of them, but then again, whom would you be fooling?

 

[JLam]

(cue the sound of christophera's head asploding.)

 

[rwguinn]

Da&n--
Now I'm gonna have to look up the answers--and I am an inj--enju--engineer...

 

[The Almond]

Da&n--
Now I'm gonna have to look up the answers--and I am an inj--enju--engineer...

In truth, all of those questions are pretty basic 1st and 2nd year engineering school questions. I just picked them because they defy common sense.

 

[Horatius]

For each of these questions, provide your common sense, non-math based answer:

1) Structural Engineering

a) What loading per square length unit should be employed for office spaces in calculations for live load?

That's easy. 6000 squirrels per cubic furlong.

b) Which will produce greater deflection on a cantilevered rectangular beam: A single point load at the end of the beam, or a distributed load equal to half of the point load over the entire beam?

Now this one makes me wonder. My gut reaction is to say the point load, but that seems so obvious that it doens't fit in with the spirit of your post. Now I have to go do math

 

[uk_dave]

In truth, all of those questions are pretty basic 1st and 2nd year engineering school questions. I just picked them because they defy common sense.

Oh...I thought it was your homework

 

[UTGrad3920]

Of course if you have common sense you would be able to read the question and immediately "know" the answer to each question without having to go through "calculations". Just like you can watch a video of a collapsing building and know through common sense what made it collapse. When do you think people will get fed up and let our homes and offices be built from common sense instead of the government conspiring to waste our precious tax dollars hiring expensive engineers to go through all this useless math to build simple structures?

 

[rwguinn]

In truth, all of those questions are pretty basic 1st and 2nd year engineering school questions. I just picked them because they defy common sense.

No--no--Don't read me wrong
I was stating I have to look them up, (or calculate them) because they are potentially counter-intuitive.
As an engineer, I back up my intuition with numbers. Intuition has proven to be remarkably unreliable, judging by past experience.

 

[Minadin]

1) Structural Engineering

a) What loading per square length unit should be employed for office spaces in calculations for live load?

Common sense tells me that it should be about 100lb / square foot cause the average "larger" office worker weighes maybe 200 lbs, but if their that big, they are gonna take up at least 2 square feet even if the office is really crowded . . . or something.

b) Which will produce greater deflection on a cantilevered rectangular beam: A single point load at the end of the beam, or a distributed load equal to half of the point load over the entire beam?

Do you mean that the total weight of the equally distributed load is half, or the load per linear foot is half? Because it seems like a diving board (probably a poor analogy) would bend more if I was standing at the end of it rather than laying down along its length, however, if you spaced a bunch of kids about half my size equally along the entire board, that might make it bend more, I would have to go get my book from the back room again and figure it out to be sure.

 

[The Almond]

As an engineer, I back up my intuition with numbers. Intuition has proven to be remarkably unreliable, judging by past experience.

Mine too. Just Tuesday, I finished the design for a soil nail wall that required only two nails for the 15 foot structure. I must have redone the calculation 10 different times with different soil and steel properties because I was sure I'd need at least 4.

We don't even trust computer programs, either. I've been on projects where fully half of the calculations done by a computer were rechecked by the engineers. Naturally, the calculations were correct, but it seems like engineers don't trust computers, intuition or even one set of calculations. We check, re-check and finalize in order to design something.

Do you mean that the total weight of the equally distributed load is half, or the load per linear foot is half? Because it seems like a diving board (probably a poor analogy) would bend more if I was standing at the end of it rather than laying down along its length, however, if you spaced a bunch of kids about half my size equally along the entire board, that might make it bend more, I would have to go get my book from the back room again and figure it out to be sure.

What's with all of these questions? Shouldn't your common sense allow you to intuit the answer to the question by making approximations and assumptions? Why do you need to know the specific loading conditions? Are you going to do the calculations? [/sarcasm]

On a side note, your characterization of a diving board is a perfectly valid one. My structural mechanics prof. used video of people using diving boards in his lectures on force and deflection.

 

[Horatius]

We don't even trust computer programs, either. I've been on projects where fully half of the calculations done by a computer were rechecked by the engineers. Naturally, the calculations were correct, but it seems like engineers don't trust computers, intuition or even one set of calculations. We check, re-check and finalize in order to design something.

GIGO, right?

Back when I was TAing physics for first year engineering students, I had a group of them ask me to critique a presentaion they were doing, on deflection of a simple rectangular bridge vs. an I-beam shaped bridge. At one point they showed a deflection vs load calculation that was way out of line - like 1 m deflection per 1 N Load sort of thing. They had simply taken the numbers as they came out of the computer without thinking about it, so they didn't notice they had seriously dropped the ball somewhere. Very embarassing, but hopefully they learned something.

And that wasn't the only time I saw that effect. One involve figuing the muzzle velocity of a spring loaded cannon we used in a projectile motion lab. I had one physics student calculate a velocity so low, it would have taken 9 years to go 1 meter.

 

[The Almond]

GIGO, right?

And that wasn't the only time I saw that effect. One involve figuing the muzzle velocity of a spring loaded cannon we used in a projectile motion lab. I had one physics student calculate a velocity so low, it would have taken 9 years to go 1 meter.

You bring up an interesting point, it may be that common sense can indicate that something may be wrong, but it certainly doesn't prove it. Your students still had to go back and determine at what point theri calculations went wrong. What type of grade would you have given them had they said, "We think it's wrong but we can't tell you why."

 

[Horatius]

You bring up an interesting point, it may be that common sense can indicate that something may be wrong, but it certainly doesn't prove it. Your students still had to go back and determine at what point theri calculations went wrong. What type of grade would you have given them had they said, "We think it's wrong but we can't tell you why."

Well, it would have been hard to give a worse grade than they already had, but I'd've tried

But yeah, knowing there's an error is only the first step. Without being able to figure out where you dropped the ball, you don't actually learn all that much.

 

[Anti-sophist]

b) Which takes up more space, 1 Mol of Hydrogen Gas or 1 Mol of Radon at constant temperature?

This question seems underconstrained to me. PV=nRT, afterall.

 

[The Almond]

This question seems underconstrained to me.

Did your common sense tell you that, or does your understanding of basic gas law tell you that you need to keep temperature and pressure the same to determine the answer?

 

[The Almond]

OK, just to record, Christophera visited the website at about 11:30am this morning (Eastern US time) and didn't make any response to the thread. Now there's ample time for him to have viewed this, and now to research the answers. Just putting that out there.

 

[Anti-sophist]

Did your common sense tell you that, or does your understanding of basic gas law tell you that you need to keep temperature and pressure the same to determine the answer?

I cheated and used the equation. I am the worst scientist ever.

 

[The Almond]

I cheated and used the equation. I am the worst scientist ever.

Nah, you're just a cheater.

 

[The Almond]

Any chance I'm going to get your thoughts on this Chris?

 

[crucial_fiction]

I only read the questions and not the rest of the thread. I believe that I should be pretty spot on for the most part.



1.)
a. 7
b. Pluto was deemed not a real planet so this question doesn't make any sense.

2.)
a. KFC originated in Corbin, Kentucky I believe, not Jacksonville, Florida.
b. Yes, at a certain point in history, Pirates were indeed in the Carribean
c. I prefer Mountain Dew to Pepsi, even though they are bottled by the same company.

3.)
a. I dunno
b. Sometimes, but usually on thursdays
c. I'm kinda stiff right now

4.)
a. Honestly what does this have to say about modern society?
b. Only if you suspend all belief
c. I think if you have 5 people in a pool the PH will go up if they all pee at the same time...


Where's my prize?