Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Helen Stohlman on 31/05/2008 18:27:21
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This question has occurred to me this week since my Guatemalan adopted grandmoher died. Here, pallbearers actually carry the coffin on their shoulders through the streets. I helped to carry Mama Naya, but at 1.83 meters I tower over Guatemalan women and am taller the vast majority of men. I took my turn with five men (3 on each side); I was the tallest of all of them, and several people have commented to me that I would have had to bear more weight since I'm taller. This seems counterintuitive to me - if I'm taller, the coffin is slanted downward away from my shoulder, and I would think that the person across from me would bear more weight. I tried to bend my knees so as not to overburden the guy next to me; but was I actually giving him more weight that way instead of less?
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His shoulders are further from the Earth's surface so the pull of gravity would be less. Not that he'd notice.
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It all depends how the pall bearers of different shoulder heights are positioned, if on one side you have one tall guy at the front and one tall guy on the back with a short guy between them he will have to carry very little of the weight.
A skilled undertaker will position the bearers for the best sharing of the load but considerations of prestige might make this difficult.
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if you put all the dwarfs on one side and the giants on the other, the body will slide to the dwarfs side and they will end up with all the weight.
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This is getting jolly silly, I'm sure no one would choose two dwarfs and two giants to be pallbearers. We are not burying Gandolf here. If you were the only taller guy then I think it would have been the guy in the oposite corner that had more weight but then we have to think about the dead persons centre of gravity which is going to be around the chest area. If you were at the front of the coffin these two factors would have balanced out somewhat. This is demonstated in magic acts when a magicians assistant can be lying flat balancing on only one chair placed at her centre of gravity. There are a lot of factors here.
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I'm not sure what a Gandolf is, but Mama Naya was just a small woman. The casket was much heavier than the body. I was at the back next to the next tallest man, about three inches shorter than I am. Those in the middle and front were a bit shorter. I was definitely the giant in the situation, as Guatemalans are short and I am not! BTW, I am a woman, but I carried with the men because I'm too tall to join the women.
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I don't think that the angle of the casket will make any difference to how it weighs to the people carrying it. For example, when we put two tall people at the back of the casket and two short people on the front, and then stand them on level ground, the casket will be tilted froward but when we then move them onto a slope of the right gradient, the casket becomes level.
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It is not a trivial question and depends upon the actual geometry of the situation but take the simplest model.
Imagine the pall bearers (A,B,C,D, clockwise) are of equal heights and the 'load' consists of a mass where the diagonals cross (i.e. the middle of the box) and it is on the floor of the box. They will be carrying 1/4 of the load each and you can replace them with 4 spring balances. Raising one corner (A) will increase the load on that corner because, if you take moments about the opposite corner (C), you will be reducing the loads on the other two (B,D) corners. If you take moments about a line through the corners (B,D) the load on the corner (C) will also increase, to be the same as the load at (A). The total of the four loads will always be the same.
In the end, if you lift high enough, you and your diagonal partner (A and C) would be lifting the whole load between you and the other diagonal loads (B and D)would be zero (apart from a bit of force to balance the arrangement a bit.
Real people are not the same as spring balances and will react to changes by compensating, raising their arms and even pushing and pulling laterally to avoid the load sliding. Also, the centre of mass of the load would be above the plane of the shoulders of the bearers, so raising one end or one side will tip the CM in the direction of the lower bearer(s) and increase their load. The effect 'side to side' would be greater than the effect ' end to end' because the angle of tilt would be greater for a given difference in bearer height.
Having the two short ones one end and the two tall ones the other end would be 'fairest'.[diagram=349_0]
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Aha! I knew it had to be more complicated. They do their best to place people of similar height next to each other, but what happens when only one (me) is taller? I'm 1.83 meters and the next tallest guy is about 1.75. In your picture, I was D and he was A. Plus there six, so there was one between A and B and one between D and C. All of these people were shorter, matched from side to side. I did try to compensate by bending my knees.
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I guess that yours was the least worst configuration. I think B would have suffered a bit until you bent your knees.
It was hardly the situation for experimentation, though. Try it with three friends and a table, sometime.