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I came up with a short quiz and posted this on another board. I just wanted to see how savvy folks were around here. I'll post the answers later if I need.

Here are a few questions to challenge those on their basic high school level scientific knowledge. Scenario: With all that heavy holiday eating, you're concerned about your health, and you're preoccupied with your weight, so you monitor it every chance you get.

1A. You step on a set of scales marked in U.S. customary units. What is your weight?

1B. What is your mass?

2A. You step on a set of scales marked in SI (metric) units. What is your weight?

2B. What is your mass?

3. You have been selected to crew on the moon station for a month. Your doctor lends you his balance scales, and you have a set of spring loaded bathroom scales as well. Mission control says you can take one scale but not both. Which one do you take, and why?

4. On the flight to Houston, you step on the bathroom scales in the lavatory of your 747 while it is on the ground. Your weight is 170 lbs. After you take off, the Captain informs you that the plane has attained a constant climb rate of 1932 feet per minute (that's 32.2 feet per second, or 9.8 meters per second, for you metric people. We're keeping the numbers simple here). You step on the scales again - what do they read?

5A. You get to the moon. You pull out your doctor's balance scale and weigh yourself. What is your weight?

5B. What is your mass?

(Hint - the moon's gravitational pull is approximately 1/6th of earth's.)
 

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Don't read any answers until you post your own.










1A. You step on a set of scales marked in U.S. customary units. What is your weight?

205 lb

1B. What is your mass?

6.36 slugs

2A. You step on a set of scales marked in SI (metric) units. What is your weight?

Probably reads 93 kg, but should read 913 N

2B. What is your mass?

93 kg

3. You have been selected to crew on the moon station for a month. Your doctor lends you his balance scales, and you have a set of spring loaded bathroom scales as well. Mission control says you can take one scale but not both. Which one do you take, and why?

The answer you're looking for is balance scales because they will read the same regardless of gravity. I would take the bathroom scales though because they are much more portable, and I can divide by 6.

4. On the flight to Houston, you step on the bathroom scales in the lavatory of your 747 while it is on the ground. Your weight is 170 lbs. After you take off, the Captain informs you that the plane has attained a constant climb rate of 1932 feet per minute (that's 32.2 feet per second, or 9.8 meters per second, for you metric people. We're keeping the numbers simple here). You step on the scales again - what do they read?

170 lbs. - almost got me.

5A. You get to the moon. You pull out your doctor's balance scale and weigh yourself. What is your weight?

170 lbs.

5B. What is your mass?

5.3 slugs
 

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Welcome to highscool physics.


1a. 170lbs
1b. No idea what the english unit of mass is, but i think its still pounds, or maybe troy pounds, or some other rediculous unit.
2a. some large number of newtons
2b. about 80kg
3. I'm going to be a smartass. I'm going to take the spring scales and a calculator, to convert in lesser gravity. It costs something like $20k to bring a pound into orbit, and I dont feel like ripping off the taxpayer just so that I can have my balance scales
4. 340lbs at 2g's. Not that I would ever get that far because the planes wings would rip off long before that. its a 747 for farks sake
5a. still 170lbs, balance scales dont care what the gravity is, as long as there is one.
5b. still around 80kg

Wtf is the hint for? I suspect you ment to ask the question with spring scales, or you are just trying to confuse people.


Edit: crap, got me with the plane...
 

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Discussion Starter #5
Heh, heh, heh. Good, good.

FYI a 747 has an operational load factor limitation of 2.5 g's. New aircraft, including heavy airliners, are certified for a minimum load factor of 3.8 g's in the normal category.
 

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Really? Damn, that would be pretty damn frightening.
 

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Discussion Starter #7
Not really. A constant 60 degree bank is 2.5 g's. In fact, Airbus flight computers limit the maximum bank angle of 60 degrees just so that limit isn't exceeded. And it's very easy to exceed 2 g's in moderate turbulence.
 

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Learn something new every day...

Here is my favorite question to make smart people feel stupid (best used verbally)

Whats two plus two devided by two?
 

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Discussion Starter #10
2?

As a side note, the secondary English unit of mass is the pound-mass (lbm), which, by definition is 1 slug/32.2. This is so one lbm will numerically approximately equal one pound-force (lbf, primary weight unit) when placed on a scale. And in fact, most balance scales that display pounds actually are calibrated in lbm, which is a mass. (Since the actual acceleration due to gravity is 31.some odd and variable number feet/sec/sec, 1 lbm doesn't exactly weigh 1 lbf. The difference is less than the accuracy of a normal balance or scale so we don't worry about it.)

Also, and this really screws with people when doing complex thermodynamic calculations between the units, but in the metric system, mass (grams) is a base unit, and weight (newtons) is a derived unit, calculated from mass. In the English system, it's opposite - weight (lbf) is a base unit, and mass (the slug) is a derived unit. A slug, by definition, is the mass that will incur a force of 1 lbf when subjected to an acceleration of 1 ft/sec/sec. Likewise, a Newton is the force incurred when 1 kg is subjected to an acceleration of 1 m/sec/sec. Note that neither system uses gravity in the definition of either force or mass.

(EDIT: I think I received payback)
 

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I think the rule of thumb is not to do any complex calculation in english units. Thats just asking for trouble
 

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Kevlar7R said:
3. Order of operations gets em.

2+ (2/2)=3
2+ (1)=3
This was the value I would have indicated for exactly the same reason.
 

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Discussion Starter #13
Just as an update:

sportbikes.com - 3 for 3 (very good) And those that got stumped by the plane problem at least understood why so that counts. Good job.

gsxr.com - 0 for 4 (very bad) but at least some people attempted it, and a couple had some of the basic concepts.

sportbikes.ws - 0 for 5 (even worse) nobody even tried to answer it.

gixxer.com - (yeah right!) I didn't even try it.
 

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Oh, cmon, no stuntlife.com or uponone.com?
 

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Lol, well I vote you throw it from the roof and measure the time it takes to land.
 

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Kevlar7R said:
Well, at least that confirms my assumption that we are the intellectual hooligans.

:)

Here is a thought provoker for you:

You wish to determine the height of a building. The only instrument available is a barometer. How would you go about determining the height of the building?
Using shadows ;)
 

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Vash said:
Oh, cmon, no stuntlife.com or uponone.com?
:laughing: Oh man, wrong timing. Got some smoked ham stuck in my throat from that one.
 

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How about going to the janitor and saying "I'll give you a shiney new barometer if you tell me how tall the building is"
 
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