Timeline for Horizontal Rack of blocks revisited a.k.a. if it were on top of lava, which block would you choose to stand on?
Current License: CC BY-SA 4.0
14 events
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| Apr 25, 2021 at 23:45 | history | edited | Roger Wood | CC BY-SA 4.0 |
failed to read the question properly.
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| Apr 25, 2021 at 23:07 | comment | added | silverrahul | I re read Pavlo's answer. Cant say i understood it completely, but i agree, it is good answer. But he said, he will add further things and explain better, but does not look like he is gonna anymore | |
| Apr 25, 2021 at 22:35 | comment | added | Roger Wood | I'm more impressed now with @Pavlo. B. answer. There are two modes of failure. | |
| Apr 25, 2021 at 22:26 | comment | added | Roger Wood | @silverrahul It seems like this mode of failure will compete with the 'friction' mode. It seems obvious that the bridge will fail anyway if the friction coeffcient is very small. | |
| Apr 25, 2021 at 22:25 | comment | added | Roger Wood | @silverrahul I see what's happening. I re-read your question again, and there is nothing to say that the end interfaces are separated by a fixed distance or remain vertical. There is only a statement about the horizontal normal forces through the stack being fixed. I now agree. The bridge can also fail especially with the weight at the center. This will occur via the rotation of the blocks when the torque provided by horizontal force acting at the top of the block is no longer sufficient to prevent the rotation. | |
| Apr 25, 2021 at 21:54 | comment | added | silverrahul | At the end of the day, whenever intuition clashes with our model, either our model is wrong or our intuition is wrong. Of course, the ultimate test would be experiment, but i am too lazy to do a proper controlled rigorous experiment. | |
| Apr 25, 2021 at 21:47 | comment | added | silverrahul | I had tried with toy alphabet blocks, and my intuition was not wrong. Of course, the 2 variables can be the horizontal force applied and coefficient of friction. But , i am not sure how they would matter. As long as the horizontal force and coefficient are high enough to hold them in equilibrum, i do not see how they can change the central block from weakest to strongest | |
| Apr 25, 2021 at 21:41 | comment | added | Roger Wood | @silverrahul In re-reading your question, I'm hearing that your 'real life' corresponds to your intuition that the middle block is least safe. I have the same feeling, but I suspect that it arises from the fact that the distance to leap to safety is a maximum. I think our intuition is wrong. | |
| Apr 25, 2021 at 21:04 | comment | added | silverrahul | " It's usually the case that you have to conjure a simple enough version that you can actually solve it, " Yes, in most examples, a relatively simple version with few assumptions and idealisations is able to explain the real result. But in this case, no one is able to explain the real life result with any kind of simple version ( or with a complicated version for that matter ) | |
| Apr 25, 2021 at 21:01 | comment | added | Roger Wood | @silverrahul Hah, yes, real life is tricky - too many variables. It's usually the case that you have to conjure a simple enough version that you can actually solve it, An added advantage of a simple model is that it can often be parameterized and can give some insights into the behavior over a range of parameters. | |
| Apr 25, 2021 at 20:46 | comment | added | silverrahul | Yeah, a fun question that no one seems to be able to give a straight answer to. Most answers seem to be unable to explain what would happen in real life | |
| Apr 25, 2021 at 20:38 | comment | added | Roger Wood | @silverrahul I have no idea. Unless the friction has a very simple form, you would have to calculate it numerically. It may also depend on the sequence in which the load is applied in time and position. e.g. is it best to step straight to the middle of the bridge, or creep in gradually from one end, or get yourself lowered very gradually from a helicopter? - it's certainly a fun question! | |
| Apr 25, 2021 at 19:00 | comment | added | silverrahul | So, if i got this right. then you are saying, in case A, standing in center is best. In case B, standing wherever does not matter. If these are the 2 extremes, what happens in real systems ? what is between these 2 extremes of "center is best" and "it does not matter" ? | |
| Apr 25, 2021 at 18:42 | history | answered | Roger Wood | CC BY-SA 4.0 |