A test of your common sense

Over the years, the most potent argument coming from the creationist side is that you can use common sense to solve everything and that you don't need no scientist or engineer to tell you how the world works. I've been on this forum for a while, and every time I think of this topic, buzsaw and riverrat (god bless their souls) always come to mind.Here is a very simple elementary engineering problem. We have a beam that is 3L long. There are 2 force acting on the beam at equal distance from the ends. If this beam is to fail, where will it fail and why?Here's a quick drawing that I made. THe reason I chose this example is because lately I've been noticing that most people have misconceptions about this. I'd argue that this example represents normal everyday thing that most people deal with. And yet, most people appear to be oblivious when it comes to this simple problem.Edited by Taz, : No reason given.

Where ever God wants it to fail. God wanted it so.

Your description and diagram are incomplete. I presume you meant 2 forces located L units away from the endpoints of beam, at points marked B and C, equal in strength P, pressing downward. One end of the beam, marked D, rests on a cylinder of circular cross section such that all right side endpoints of the beam rest on the top of the cylinder. The other end of the beam, marked A, rests on a triangular parallelepiped with a right triangular cross section, with the right angle edge on the ground directly below all left side endpoints of the beam. The beam is also presumed to be a rectangular parallelepiped. I also assume that the limitations of drawing the diagram prevented making the top of the triangular parallelepiped exactly meet the bottom of the beam, rather than penetrate into it as shown.Is this correct?BTW, I have never seen this problem come up anywhere in my life. When you say "most", how many is that? What "normal everyday thing" is this a representation of?Edited by xongsmith, : further issuesEdited by xongsmith, : No reason given.Edited by xongsmith, : No reason given.

I agree with xongsmith on most points.This is not part of my common experience.The statement of the problem is incomplete.Based only on the picture, and assuming that the ends are just sitting there, it looks as if the beam would warp enough for one of the ends to slip off its support.I'm guessing that is not what you are asking, though it illustrates the incompleteness.Otherwise, I would expect it to fail near the center. There are upward force at A and B, that counter the downward forces (plus the weight of the beam). Between the upward forces and the downward forces, we have attempt to rotate the left part and the right part in opposite directions. That is, the combined effect will be to warp the beam. This attempt to warp will be resisted by the tensile strength of the beam, and I'm pretty sure that will be at a max near the mid point.

Assuming the beam was rigidly fixed at A and able to move on roller at D, I think the greatest stress would be at A - The beam would fail at A (the support/beam connection at A would fail).Contrary to NWR's view, I think the least stress would be a the middle point.Moose

Again, there are many things left out. Is the triangular support made out of carbon steel, the beam made out styrofoam and the circular support a big soap bubble? Are the 2 forces P carrying the weight of dustmotes or asteroids the size of Ceres? Are there lateral perturbations distributed around the application of each force P at points B and C? Are they big enough to make the triangular support fall to the left as the right end rolls off the cylinder? Can the cylinder even roll freely? When Taz says "fail" does he mean fall down or snap apart? Or does he mean Either One, whichever comes first? All of the relative tensile strengths and characteristics of the static stability of the elements have to be specified in a far greater detail than one would need if it were to be able to be merely categorized as a "simple" problem. The diagram leaves out a presumed solid ground underneath, but what if it is correctly drawn as only thin air?But most of all, what in the world is this "common every day thing"?

I say it fails in the middle, dead center, because that's where the combined moment is longest. No real idea, though. Edited by crashfrog, : No reason given.

Hahaha, you guys are funny.There's a reason why I said use your common sense rather than real engineering knowledge.And if you can't use everyday example to reflect this, then your imagination sucks.Instead of thinking beam, think other things. If we have just a single load in the middle then obviously when the beam/plank/car/board/person fails it's going to fail in the middle. That's where the greatest stress is. The point I'm trying to make is what if you have 2 loads like the drawing? When the beam/plank/car/board/person fails, where will it fail?By the way, xongsmith, that's a lot of BS.

Thank you! Your reply is the most common misconception that I was referring to. Most people would say the middle, which is of course wrong.The point of this thread is this is a relatively simple problem that reflects a very common everyday thing that people encounter. If you can't apply this example to real life example, then your imagination sucks. Anyway, despite how simple this example is, it's almost impossible to solve this with just common sense. And that's my point. Over the years I've seen many many creationists put all their money on common sense. I'd like to see them solve this problem using common sense.Any other taker?By the way, xongsmith, where did you learn all that mumbo jumbo?

Sorry you see it as BS, Taz. But you can't just have one end be a triangle about to tip over to the left and other be some metal tubing or something. Make your example identical at each end. Make all of the materials the same. Make it simple so that there is a simple solution that can be mis-intuited through "common sense".Just trying to help.You say: Too which I reply: Edited by xongsmith, : soapbox utteranceEdited by xongsmith, : whoops i meant mis-intuited

Hey, I'm not afraid to be wrong. Glad I could be of service!Any chance you could PM me with the right answer? My curiosity simply can't wait.

Hi again Taz...Not to be troublesome, but could you give me some kind of a clue about these questions I asked in Message 3: "Most" in my neck of the woods usually means "more than half".This may actually be off-topic, but you claimed that "lately I've been noticing that most people have misconceptions about this. I'd argue that this example represents normal everyday thing that most people deal with." For example, most people do not have any everyday experience carrying a load of bricks across a plank.Maybe you meant to say something along the lines of "this represents a simplified abstraction of certain events in ordinary life." This is similar to first studies of the quantum dynamic wave function of an atom where they first begin by assuming the atom is a spherically symmetric object, then add in the other terms.

I can't apply that example to anything in real life. I can't even determine whether you are trying to show something, misdirect attention or just plain don't know how to make a drawing.

OKAY.......my hipshot, common sense guess, without the needed information Taz left us to assume......assuming the drawing is as i assumed in Message 3, and that the whole experiment apparatus is perhaps on a carpet-ish unyeilding surface where the triangular support cannot slide on it, but the circular support can roll on it, and that all parts of the experiment are unattached in any way, whether by glue or magnetism or molecular attraction otherwise and that the beam, being of this world and subject to the visual recognition of common sense eyes, is ordinary and will bend some before it breaks, the "Fail" here must be a fall first, not a break - unless he defines it as a break, in which case we follow the fall down. Here is why:The beam will begin to bend before it breaks, making the endpoints A and B on it get closer together by an infinitesimally small amount at first. At this infinitely small step in time, the 2 ends move towards the middle, meaning that the end on the left drops precipitously down the triangle while the right end still rides pretty high on the circle. The next infinitesimally small increment in time finds the left end splaying out the triangular side, being a right angle triangle positioned so badly for the beam, lifting it's right corner off the rug, while the left side begins to slide off the circle, rolling it away to the right. Because Taz drew the right triangle not isosceles but 3-4-5-ish with the 5-ish pointing up, the left side is quicker to descend overall and quickly the hypotenuse meets the beam with an audible snapping sound. Then the circular descending rolling-away motion at the right completes and the right end touches the rug first. It is at this point that the relative power of the 2 forces, P, come into play. The one on the right initially got to bear down harder as the left side fell faster, but then the hypotenuse ended that and the one on left got a jolt of stubborn resistence. I suspect that, now, the common sense world beam, if "failing" meant breaking before falling, would break on the left side just fractions of a second before the right side gave way. By the time the P on the right gets to hit the beam full on, it is already on the ground, too late, and might even bounce.That would be my hipshot, common sense angle on it, assuming all the things I had to assume about Taz's ill-formed statement of the problem. These assumptions could be way off, yes.

Assuming whatever the beam is sitting on is stable and won't move, I would say it will fail at B and C. There's no stress on the middle. The stress is going to be from the pressure points to the ends.Two kids bouncing on a board. Fun till it breaks.