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Important question I need help with because I'm being stupid.
Alright, you have rod with a circular cross section made out of some material, hanging from a ceiling.
We can take its tensile strength (Pa = kg*m*s^-2*m^-2) and divide it by density (kg*m^-3). We are left with specific strength, kind of like the weight to strength ratio in units of m^2/s^2. Now we can divide this by the acceleration due to gravity, to express the specific strength in meters. This value tells you how long of a single cross section beam you could hang from a ceiling before breaking.
For example, steel is around 6km, aerospace aluminium is 20km, the strongest metal is titanium at 29km, so on and so forth. However, you could make the cross section thinner near the end where it doesn't carry much stress, and add it on to the bottom, to make the rod longer.
My question is, what would be the function of the radius of the length from the top of the ceiling be (in the axial component of the rod), if given the radius at the bottom and top of the rod, in order to maximize the length of the structure (cross sectional area as a function of length is fine too of course). Please help, my curiousity is getting the best of me, and I'm struggling to obtain an answer 
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United States44439 Posts
Bullshit. This is clearly a Google interview question.
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Does the elevator "close door" button do anything?
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Norway28923 Posts
closes the door slightly faster?
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ZigguratOfUr
Iraq16955 Posts
On September 04 2016 05:50 Epishade wrote:
Does the elevator "close door" button do anything?
Depends where you are in the world. Often not in the US (due to 4.10.7 of the ADA), unless you have the key.
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On September 04 2016 06:17 ZigguratOfUr wrote:Show nested quote +On September 04 2016 05:50 Epishade wrote:
Does the elevator "close door" button do anything? Depends where you are in the world. Often not in the US (due to 4.10.7 of the ADA), unless you have the key.
it says :
"The minimum acceptable time from notification that a car is answering a call until the doors of that car start to close
shall be calculated from the following equation: T = D/(1.5 ft/s) or T = D/(445 mm/s) where T total time in seconds and D distance (in feet or millimeters) from a point in the lobby or corridor 60 in (1525 mm) directly in front of the farthest call button controlling that car to the centerline of its hoistway door. For cars with in-car lanterns, T begins when the lantern is visible from the vicinity of hall call buttons and an audible signal is sounded. The minimum acceptable notification time shall be 5 seconds.
Elevator closing time is serious business.
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I'm sure private elevators don't give a shit about regulations though
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I read somewhere that the close button is often (usually?) disconnected, but even then has a psychological effect.
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Skip to floor trick doesn't work anymore since everybody caught on, only firefighter key works now.
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On September 04 2016 00:59 KwarK wrote:
Playing by the rules that the state murdering all the babies sets would be absurd. It comes down to ongoing baby genocide and how far you're willing to go to stop it. And throwing a bomb in an empty abortion clinic would definitely save a lot of babies. It's not a vague terrorist political gain or raising awareness of the issue, it's like sabotaging the gas chambers. The outcome is the goal. The only reason not to is a social agreement the state claims it has with you that demands your consent to its genocide.
I think you're fixated on the state. The issue is society, the demos, us folks. There is no stopping the "baby genocide" by force. It cannot be done. So your remaining sane options are to either flail wildly with no end goal in mind (as you are proposing) or else actually work toward defeating the evil.
The problem is that you can't fight the problem with violence because you gain some small thing (make a few abortions impossible) but lose a far larger thing (the goodwill of people around you).
There's also the important point that being pro-life presupposes a principled stance in favor of the preservation of life, which refuses to admit exceptions for practicality. Violence is obviously antithetical to that. Now, mind you, plenty of pro-life folks are ok with violence in other spheres, but I like to argue against the most reasonable position available. Which might be the principled pro-life stance of, say, Catholicism, which argues against everything that cuts life short: war, abortion, euthanasia, suicide, the death penalty etc.
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On September 04 2016 03:46 FiWiFaKi wrote:Important question I need help with because I'm being stupid. Alright, you have rod with a circular cross section made out of some material, hanging from a ceiling. We can take its tensile strength (Pa = kg*m*s^-2*m^-2) and divide it by density (kg*m^-3). We are left with specific strength, kind of like the weight to strength ratio in units of m^2/s^2. Now we can divide this by the acceleration due to gravity, to express the specific strength in meters. This value tells you how long of a single cross section beam you could hang from a ceiling before breaking. For example, steel is around 6km, aerospace aluminium is 20km, the strongest metal is titanium at 29km, so on and so forth. However, you could make the cross section thinner near the end where it doesn't carry much stress, and add it on to the bottom, to make the rod longer. My question is, what would be the function of the radius of the length from the top of the ceiling be (in the axial component of the rod), if given the radius at the bottom and top of the rod, in order to maximize the length of the structure (cross sectional area as a function of length is fine too of course). Please help, my curiousity is getting the best of me, and I'm struggling to obtain an answer
I haven't done this kind of mechanics, but seems like a pretty basic differential equation? I'm on my phone though, so bear with me...
The strength scales with cross section. The mass to carry is the cross section integrated over the length underneath. So if you want to be on the carrying capacity at all points, let L be the length from the top, and a(L) the cross section at that point:
a(L) proportional to integral{of x from L to infinity} a(x) dx = A(infinity) - A(L),
where A(L) is the primitive function of a(L). Set the proportionality constant to 1 for easier notation (I'm on a phone) and take derivate wrt L:
a'(L) = -a(L)
Which solved by
a(L) = exp(-L).
The radius, being the square root of the area, is still an exponential.
It kindof makes sense that it's an exponential, so that the thickness at any point of the"thread" does not depend on what is happening above it, only below. Doesn't know where the ceiling is.
Edit: you can trace all the constants pretty easily if you want, but not doing it on the phone...
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On September 04 2016 07:21 OtherWorld wrote:
I'm sure private elevators don't give a shit about regulations though
At least here in the US, all elevators have inspection requirements in all 50 states, usually administered via municipal building inspectors.
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Norway28923 Posts
speaking of elevators, I've been really amused by the concept of the sabbath-elevators used in areas with large numbers of super orthodox jews. Basically they're programmed to just go up and down and stop on every single floor - because even something as small as operating an electronic switch is too much work for the sabbath.
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Something I have always wondered: " If you lay down straight on your bathroom floor, could you use the bathroom scale to weigh your own head?" I don`t have a scale at this time, but I have heard that most of the TL staff have bathrooms. Could anyone post the findings ?
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On September 04 2016 21:13 SPcrusader wrote:
Something I have always wondered: " If you lay down straight on your bathroom floor, could you use the bathroom scale to weigh your own head?" I don`t have a scale at this time, but I have heard that most of the TL staff have bathrooms. Could anyone post the findings ?
Yes, you could, but it wouldn't be very accurate. I also don't have a bathroom scale, but the results will vary by how much of your head/neck you put on the scale. And of course, the force you yourself exert on pushing your head up or down.
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On September 04 2016 21:13 SPcrusader wrote:
Something I have always wondered: " If you lay down straight on your bathroom floor, could you use the bathroom scale to weigh your own head?" I don`t have a scale at this time, but I have heard that most of the TL staff have bathrooms. Could anyone post the findings ?
I think I'd like you to provide a source to the statement that most of the TL staff have bathrooms. Heard from where? It's not really good practice to just throw statements like that around without better motivation.
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On September 04 2016 21:13 SPcrusader wrote:
Something I have always wondered: " If you lay down straight on your bathroom floor, could you use the bathroom scale to weigh your own head?" I don`t have a scale at this time, but I have heard that most of the TL staff have bathrooms. Could anyone post the findings ?
Who would do such a thing, it's clearly a waste of time... On a completely unrelated note, my head weighs 6.125 kg
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Ok, this is going to be an odd one. After having spend way to much time on r/unexpectedjihad/ I really, really need the song that is used in this video: + Show Spoiler +
I find it really relaxing but haven't managed to find it without "alahu akbar" shouts or in acceptable quality. If there is a clean high quality recording of this please send me in its direction.
EDIT: Name of the song would also help but propably not that much...
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On September 04 2016 21:13 SPcrusader wrote:
Something I have always wondered: " If you lay down straight on your bathroom floor, could you use the bathroom scale to weigh your own head?" I don`t have a scale at this time, but I have heard that most of the TL staff have bathrooms. Could anyone post the findings ?
I'm afraid you'd would get a lot of variation based on the angle of your head/neck, because it'll modify how much of your head's weight is supported by your neck and thus not measure. I think the only reliable way to weight your own head is to cut it off and have someone do it for you.
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EPT
