Using your common sense to solve a physics problem.

quote:

---

So yes, I really think that science is just disciplining common sense to a point where one can apply past experiences to predict and explain future events.

---

Unfortunately, it's not so simple as "disciplining" common sense. For example, common sense told people that objects fell with a velocity in proportion to their weight. It told people that the outer planets moved forward, then stopped and turned backwards, then moved forwards again. It told people that if you have a tall, thin pipe filled with water stopped off by a cork at the base, that it will put less pressure on the cork than if you had a big tank full of water of the same height. Etc.The problem is accumulated knowledge. Only through application of accumulated knowledge can physics be solved accurately. Data must be acquired, and fit into a common framework; then one can work within the framework. It was only through huge amounts of experimentation conducted the world over that we managed to reach the state of modern physics. Even kinematics (like your problem), which we now take for granted, took a long time - and a lot of testing - to quantify.One of the big problems with creationists is that they assume the framework must be wrong. Mind you, they don't attempt to fit the centuries of accumulated evidence into a different framework; they just assume, using their "common sense", that there must be a different framework out there - something, anything - that works instead. They furthermore assume that had this framework simply been considered, all of these people who worked so hard in their evidence collecting throughout the centuries would have found that their data fit into it - all of the billions of datapoints out there.This is the antithesis of science, and it is very flawed. One of the biggest flaws is that the standard bible-literalist framework *was* the default framework used for a long time. Scientists tried and tried, to no avail, to keep it. Look at the early scientists in the fields of geology, physics, chemistry, biology, etc, in Europe - they were almost all Christians. Even today, the majority of western scientists are Christians - and a fair number of them were brought up in creationist households. Far from never being considered it, these people would undoubtedly *love* to have the bible being proven literally true. They believe in God, they believe in Christ, and just like the creationists on this board, they want to find any evidence possible that the words within that book are literally true as much as possible.

---

"Illuminant light,
illuminate me."

Heh, I had to deal with rigid body kinematics recently. Here's a good paper that covers all of the angular momentum stuff:Rigid Body Simulation I - Unconstrained Rigid Body DynamicsThe biggest question that I had when working (addressed by this paper) was as follows: Picture a long, lightweight bar with a small, dense, heavy weight on its center. If you push on the center, all of the work that you apply goes into accelerating the object forward. If you apply the force to the end of the rod, almost all goes into angular acceleration. However, if you apply the force in-between, how much goes to angular acceleration and how much to linear momentum? Also, given that 100% of the work goes into angular momentum if you push on the end, what happens if you push at both ends at once? It would seem like you would get two angular accelerations in opposite directions, they would cancel out, and there would be no momentum - but we know that it will instead gain linear momentum.The error was based on a false assumption that I had, that seems so simple in retrospect: that the work is the same in all cases. It isn't; work is force times distance, and you push for a longer distance if you push along the end of the rod. It's not an issue of "some percent of work as linear force, and the rest as torque"; it is the full linear force plus the full torque, always.

---

"Illuminant light,
illuminate me."

The bar looks like this:---------------O---------------If you push on either end, almost all the work will go into angular momentum. If you push on the weight in the center (the O), all of the work will go into linear momentum. If you push on both ends at once, the angular acceleration cancels out, but the bar accelerates linearly.

---

"Illuminant light,
illuminate me."

That's why we're dealing with "Rigid body kinematics"

---

"Illuminant light,
illuminate me."

You seem to not want to cover a basic physics problem with your common sense. Fine, given your remarks insulting engineers, lets give you an engineering problem.You're building a double-layer catwalk in a hotel. The catwalk's mass is supported by steel hangar rods that run from the ceiling, through the upper catwalk, and down to the lower catwalk; a nut on the rod 6.1 meters up from the base holds up the first catwalk, and a nut at the end of the rod holds up the second catwalk.You find that you can't get a hangar rod which will allow you to have a nut 6.1 meters up from the base. Using your common sense, what would be the ramifications of using two hangar rods - one from the ceiling to the upper catwalk (with a nut at the bottom of the catwalk), and then one from the upper catwalk to the lower catwalk (with a nut above the upper catwalk to support the rod, and one below the lower catwalk to support the catwalk)? Would it have the same carrying capacity, reduced carrying capacity, or increased carrying capacity, and if different, how much?

---

"Illuminant light,
illuminate me."

How'd you do?Crash!You see, the people on-site thought they'd only be adding the weight of a bit more rod and an extra nut, too. However, if they had repeated the original structural design analysis, they would have discovered the fact that the nut supporting the upper catwalk has twice the force on it after the modification, and while you don't normally expect a nut to be a failure point, the tensile stress imposed was too much for it. See below:Original:
Modified:
Rethinking it, can you see what's going on? Originally, the *rod only* was bearing the weight of both catwalks, but after the modification, the *nut* that supports the upper catwalk *also* has to support the weight of the lower catwalk.Your "common sense" just killed 114 people. A structural analysis would have told you that the new design would put too much stress on the nut. You can't just ignore all of those tensile strengths and just build things based on looks - to know what materials can take what amounts of stress when forces combine in complex ways, you need to know your physics. Just because a nut looks like it might hold, doesn't mean it will. The only reason that the original design for the catwalk was (relatively) sound to begin with was because it *was* calculated (using physics), and that's how they knew what materials to build with, what diameter rods to use, etc.If you didn't do structrural analyses from the start, *every* building would be killing people because common sense fails way too often. You can't just "common sense" your way to the results of physics problems.That is why we find it annoying when you sit here and insult people who use science in their jobs, as if you somehow know better.

---

"Illuminant light,
illuminate me."

It wasn't the wrong sized nut. It was the right sized nut; however, it was an invalid design modification that doubled the stress on the nut. The nut was sized right to hold up the original catwalk. The "common sense" modification, however, ruined this. I asked you for the rammifications of the design change. Using your common sense, the fact that you'd have to double the strength of the nut completely slipped past you; you simply stated that you'd only have to bear the weight of a few more inches of rod and an extra nut.Do you honestly think that if we built buildings without structural analyses, that they wouldn't be collapsing all over the place?This message has been edited by Rei, 09-24-2004 12:22 PM

---

"Illuminant light,
illuminate me."

quote:

---

I think your story proves my point. The engineer can miss something, where in that situation, if I was on the job, I might have caught it.

---

But... the engineer *DID* get it right, and *YOU* got it wrong. The engineers conducted a structural analysis and determined how much the nut could hold. *They were right*. You, however, just used your common sense, figured that the structure would be safe given the modification, and completely failed. Your concept that there'd only be the extra stress of a few inches of pipe and an extra nut was *wrong*. If this had been your job, you would have been responsible for the deaths of these people.This message has been edited by Rei, 09-24-2004 04:24 PM

---

"Illuminant light,
illuminate me."

Probably the worst thing about channels like the discovery channel is sins of omission.For example, they had a show about Nefertiti, in which they postulated that Nefertiti was in fact the pharaoh Smenkhkare. They present a lot of the very real, very compelling evidence that Nefertiti was Smenkhkare. However, they omitted the information that argues against it - for example, the fact that Smenkhkare married one of Nefertiti's daughters (Ankhesenpaaten), nor discussed that something that is possibly Smenkhkare's body already exists.I mean, they don't always omit stuff; unfortunately, it happens too often to be a consistant, reliable source of information. The Nefertiti show, for example, was a lot more entertaining the way they presented it as a dedicated archaeologist, who through her efforts, conclusively overturned long-held views about one of Egypt's pharaohs. Presenting the nuance that is found in the real world isn't as entertaining, however.This message has been edited by Rei, 09-24-2004 07:33 PM

---

"Illuminant light,
illuminate me."

I asked you for the rammificatoins of the change. You said that the rammifications were that it had to support a few more inches of rod and an extra nut. You never even mentioned the increased tensile load on the first nut. Are you going to try and claim that you thought of it, but didn't think it was important enough to mention it? Because it most definitely was a serious ramification.

---

"Illuminant light,
illuminate me."

I don't care if you would have suggested that change; that is completely off topic. You were asked for the rammifications of a proposed change. You pointed only to minor rammifications, and completely ignored the major ones (which led to collapse). You completely failed, where a mathematical analysis would easily have succeeded.This message has been edited by Rei, 09-27-2004 01:25 PM

---

"Illuminant light,
illuminate me."

And when it rains, do you watch all of the water in the water cycle on Earth (which would be involved in your flood model)? Do you see the upstream and downstream rammifications of the rain? Do you get any data about the continents? Do you see ice dams breaking or glaciers melting or anything of the sort? Anything?Gee - even ignoring the fact that I think we've conclusively shown that common sense usually fails in complex problems like the one you discussed, I'd say that you have a severe shortage of data on this one as well, wouldn't you?P.S. - If you don't think that common sense usually fails in complex problems like the one you proposed, I'd like an answer to how long you think it would take Lake Mead to drain. I've computed the answer in both normal and 1000x normal influx situations (I'll want to cross-check my fluid model with someone else first) using Riemann sums instead of direct integration (yeah, I'm lazy, but it works ), so I have the answer - but if you're not yet convinced at how poorly common sense works, I'd like to hear you answer.A little data for you to make it easier on you. Lake Mead has a volume of 35.2 km^3 and a surface area of 637 km^2. Its deepest depth - at the dam - is 170 meters. The base of the dam is 201.2 meters wide; at the crest, it is 379.2 meters wide. The crest is 221 meters above the base. Its influx of water is about 700 cubic meters per second.This message has been edited by Rei, 09-28-2004 05:55 PM

---

"Illuminant light,
illuminate me."

quote:

---

What if the water on the other side of the dam was as high as the dam? where would it go?

---

That's irrelevant to the problem here. We're talking about how quickly water drains away.

quote:

---

In a global flood, things would be much different, and the water may not have anywhere to go.

---

Not possible, unless the earth is incredibly flat. In which case, you have a lot of explaining to do on why it's not today.

quote:

---

I am well aware of how fast any lake could drain out. Thats common sense.

---

And yet, you refuse to give a number. Gee, I wonder why....

quote:

---

So tell me, I live on a mountain where the slope is about 30degrees. How long would it take water to run off? The hieght is about 500ft above everything else around it. The base of it takes up about 400 acres. It would seem impossible that it would ever flood right? Well it does.

---

Tell me, how deep does the water stand on your 30 degree slope? On a real 30 degree slope (i.e., not just something that averages 30 degrees), you can make the soil *soggy*, but water can never stand more than a centimeters or so without constant influx. If you're talking about an average, you can get hills and troughs, in which some parts are above water, and others aren't. I don't think that's what you're proposing for the global flood, though, because that would still leave much above the surface.*Standing water*, when given an unobstructed path to a state of lower potential energy, moves *very fast*. The water near the base of Hoover Dam, should it collapse, would be going almost twice the speed of a car on a highway (ignoring drag; there's actually an effect in which the water *right* on the bottom moves slowly, and there's a speed gradient from there up to a few feet where it is moving at full speed). That's only 170 meters in height's worth of water pressure.This message has been edited by Rei, 09-28-2004 07:24 PM

---

"Illuminant light,
illuminate me."

quote:

---

quote:

---

That's irrelevant to the problem here. We're talking about how quickly water drains away.

---

​

No we are not, we are talking about a world wide flood, stay on topic then.

---

Wrong. Your proposed hypothesis was that areas get flooded faster than the water can drain away. So, we're discussing the ability for water to drain away. Unless you're changing your hypothesis, that is.

quote:

---

quote:

---

And yet, you refuse to give a number. Gee, I wonder why....

---

​

Bcause it is an isolated event, and has nothing to do with how fast it would drain out in a world wide flood, so it proves nothing.

---

Actually, it *does* - it shows how quickly large amounts of water drain away, so long as there is a path. Do you know *why* they drain away so fast? Because the velocity of the water is proportional to the square root of its depth - look up Bernoulli's law sometime. [quote]

quote:

---

Tell me, how deep does the water stand on your 30 degree slope

​

The top of the mountain I am not really sure, I wouldn't expect much.

---

Biiiingo!

quote:

---

But here near the bottom, the water literaly sparys out of the cracks in the rocks.

---

Let me raise a couple of words of yours to stare at for a minute:...here near the bottom...Stare at them for a minute, will you?

quote:

---

What I think is happening is, once the mountain can no longer retain water, the water has no-where to go. The hydro-static pressure builds up in the ground water, and then forces it back out the mouintain, where it would collect with the rain water and have a doubling effect.

---

Instead of postulating with no knowlege on the subject, how about you *gasp* look it up? What is the geological makeup of your mountain? What minerals are in abundance? How much fracturing is there?

quote:

---

This whole prcess gets less, and less the closer you get to the top.

---

Biiiingo...

quote:

---

But it was this process that made me think to myself, just how bad would this get if it rained extremely hard for 40 days.

---

At the top? None. It comes out of the bottom not due to some mystery pressure, but due to gravity. The water needs to go somewhere, and it wants to go down. So, it goes down. Often fractures are the easiest path. It is irrelevant whether it goes down in fractures or down on the surface of the mountain; it still goes down. The deeper the water, the greater the pressure, and the faster it moves.If the fractures fill up faster than they can discharge? It'll go over the surface.

quote:

---

Just how much would it back up, from the oceans to here. this is where my hypothesis ends, and real science has to take over.

---

It doesn't. Not a bit. The deeper water gets on a slope, the faster it moves. As I mentioned, water at the base of a 170 meter wall of water will move at around 57 meters per second (ignoring drag; however, a layer of drag will only exist right near the bottom and sides). Do the math: sqrt(2*9.8*depth). Deep walls of water get downstream *fast*. End of story.Lets clear up some details about your proposed system here.You have fractures in rock that allow water to penetrate. The main determination on how much water enters the fracture vs. flows over the surface is drag; since fractures are narrow, there is a lot of drag. The drag will be proportional to the square of the velocity, and the velocity will be linearly proportional to the amount of water flowing through. So, as the fractures near capacity, less water flows through them, and the more flows over them. In your intense-rain model, almost all of the water, consequently, will go on the surface, unless God magically changes drag.

---

"Illuminant light,
illuminate me."