GalacticCactus Forum
Forums => English & Linguistics => Topic started by: Porter on December 16, 2007, 09:52:43 PM
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On another thread, we were talking about words that are both common everyday English words and technical terms. Sometimes, such as with parts of the body, the words mean exactly the same thing.
This thread is for words that don't.
Stress, Strain, and Pressue: In common every day English, these three words mean pretty much the same thing. As engineering terms, however, they don't.
Mathematically, stress and pressure are defined identically -- force divided by area. Generally, the term pressure is used when it's something else applying the force (water pressure, atmospheric pressure, the pressure that Hulk's footsteps place on the asphalt, etc.), otherwise the term stress is used, such as the stress applied to the wings of an airplane.
Strain is something completely different. When you pull on a metal rod, it will stretch a little bit. That stretch is called strain. It is calculated by dividing the change in length by the total length.
It is worth noting that within the elastic range, strain and stress are proportional (double the stress and you'll double the strain), so while they've very different things, they're closely tied to each other.
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Is Pressue the stress caused by someone pressing a suit? With steam or in court?
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I'm guessing that you're making a joke that I don't get, but I don't really know.
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The pun has to do with a suit of clothes vs. a lawsuit. And pressing with an iron vs. bringing litigation.
Good one, pooka.
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I'm guessing that you're making a joke that I don't get, but I don't really know.
She's making fun of your typo.
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That too.
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There is also a disconnect between the scientific usage of theory as opposed to it's colloquial connotation. I think it's probably true of most things technical.
But mostly, I just wanted to use "colloquial connotation" in a sentence.
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Ooh! Theory is a good one.
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Force: That's just a unit of, well force, (:wallbash:), like pounds or Newtons.
Work: Work is defined as force multiplied by the distance that force is applied over. So I can push my house all day with 100 pounds of force, but no work was accomplished because it didn't move. But if I push my car all day, I will accomplish work, because I'll be able to move it.
Power: Work divided by the time it takes. Let's assume my little car jack can lift just as much as the nice hydraulic jacks at the mechanics. While they use the same amount of work to lift my front end a foot off the ground, the mechanic's will use a lot more power because it will accomplish it much faster.
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Mathematically, stress and pressure are defined identically -- force divided by area. Generally, the term pressure is used when it's something else applying the force (water pressure, atmospheric pressure, the pressure that Hulk's footsteps place on the asphalt, etc.), otherwise the term stress is used, such as the stress applied to the wings of an airplane.
I'm not quite sure I understand the distinction. Wouldn't there *always* be something else applying the force?
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Something else may be applying the force but not directly applying the pressure. I misspoke earlier, using force when I should have used pressure.
The distinction is rather ill-defined, and I'm not sure that there's technically any meaningful difference between the two.
Let's say for the science fair my son designs a bridge made out of toothpicks, and we analyze the amount of stress a ten pound weight would put on all the different toothpicks. Depending on the design, some toothpicks could be under 10X or 100X the stress of other toothpicks.
But the weight isn't applying more stress to one toothpick than another - it's applying one force which creates different amounts of stress.
Same with the airplane wing -- what's causing the stress on the wing while it's just sitting there? It's the weight of the wing. But the earth's gravity isn't applying pressure to that part of the wing, it's just applying a force. It's the way that the wing is cantilevered out that is causing the stress.
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*cough* engineers *cough*
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Well, yeah. I mean, I'm talking about engineering terms.
And it's not like you never sound like a nerd when talking about things you love. :)
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Oh, okay, that made a lot of sense. Thanks!
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This was a salvo in the physicists v. engineers war. While only an honorary member of the physicists, I still couldn't let the opportunity go by twice. ;)
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Hadn't you heard? There's been a treaty signed between the engineers and the physicists. We're both at war against the mathematicians.
We've always been at war against the mathematicians.
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Is it time for the two minutes hate yet?
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At GC, it's always time for two minutes of hate! :)
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Yeah, just try to tell me how weight isn't mass again. Like, I'll believe it when I see it dude.
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Weight and mass are completely different things, but as long as we remain on the earth (and aren't doing any calculations which depend on the distinction between the two), you can pretty much ignore that and pretend like mass and weight are the same thing.
But if we got to go on a field trip to outer space, you'd notice the difference pretty quick. While nothing would weigh anything, you'd still be able to tell that more massive things are harder to move -- they have more inertia.
To complicate matters, pounds is a unit of force while kilograms is a unit of mass. So if I went to the moon, I'd only be about 33 pounds, but I'd still be about 100 kilograms.
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Yeah, I guess the point was that the word "weight" doesn't really exist in physics. Just so long as they don't decide that while it's sitting around not being used, they could use it to label something else.
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Weight certainly does exist in physics.
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:pirate:
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It does! I have no idea why you'd say it doesn't.
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Hadn't you heard? There's been a treaty signed between the engineers and the physicists. We're both at war against the mathematicians.
We've always been at war against the mathematicians.
That explains so much about my parents. ;)
And of course weight exists in physics. What did you think a newton was for? :D
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What did you think a newton was for?
Wrapping around fig paste?
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A newton is the SI unit for force or weight.
The old English unit for mass is the slug, but it's become increasingly common for people to use the "pounds mass" unit, which is the amount of mass that would weigh one pound of force under exactly 1.0 gravities (32.2 feet per second squared, IIRC).
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Wrapping around fig paste?
Great TOPP.
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Mass is the concentration of combat power. :rolleyes: