Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: netrista on 19/05/2017 23:28:09
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I have a mundane energy transference question. If it's too mundane for the group, please delete or ignore as appropriate. Otherwise, my husband and I would like some assistance vetting what we believe to be a case of unexpected energy transference through the walls in our home.
Observation: My husband and I heard a loud boom in our livingroom. The dramatic sound suggested my 7ft, wooden bookcase had toppled into my wooden desk. On inspection, we discovered nothing to be the case. Instead, we found a framed picture in an unexpected location in the home. The picture is framed in wood, 1'X1' and about 3 lbs in weight. It was hung about 5'2" off the ground by a tack. It's current location suggested it was thrown at a 45 degree angle roughly 9ft across the room. The trajectory entailed that it was initially thrown somewhat upward (at least 2 inches or so) to clear a tall object that was poised in front of it. Roughly four hours later, a wooden clothing rod in abutting room crashed to the floor undeniably due to the weight of the clothes hung on it.
Theory: The curtain rod resides in a room that shares the entirety of a 10' L by 7' H, load-bearing wall with the living room. This wall is is covered with cheap paneling. The curtain rod resides in 3'7" space where a doorway once resided. It has since been covered over with a slim piece of panelling, thereby creating a closet. The opposite side of this piece of paneling is where the aforementioned picture hung. That said, the wooden rod is 1 inch think and had roughly 50 items of clothing on it including heavy coats. We suspect that tension created by the wooden rod buiilt up over the course of the day and transferred through the wall and precipitated the picture going flying. Then, of course, the rod gave way itself.
Contraindications: We can't account for the incredible noise. We can't assess why another picture (identical in dimensions) hung an inch above the first one remained in place. We can't ascertain why the rod the fell before without such a dramatic outcome. And, we wonder if transference--if possible--would cause such an incredible trajectory.
Finally, any commentary is appreciated. We are engrossed in solving the problem, as we are concerned that something like a hidden roof truss failure contributed to the phenomenon. Thanks!
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It's certainly a strange story, but one must consider simple explanations first. You don't say where you live. Might there have been a minor earth tremor that day which was sufficient to break the retaining / hanging wire of the picture and then, having weakened the curtain rail, caused that to break later.
Regarding the noise, when a big object moves a lot of air it can produce low frequency loud sounds without having to move particularly fast. Think about a hand slapped down on a table-top. A picture presents a big surface area to the floor, so it will move a lot of air as it lands, most likely accounting for the sound.
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Thanks for your reply! I found the solution to the problem after using a Work/Force/Distance calculator. The amount of force needed combined with the required angle of impact lead me in the right direction. First, note that we discovered an air pocket high on the wall behind the closet paneling. We also realized there were bags of stove pellets on the floor that had created an incline akin to a ramp. We theorized that my son had some how propelled himself up this "ramp," passed through an incredible density of clothing, struck the air pocket high on the wall, displaced the air and launched the picture across the room. This is by no means an easy feat for several reasons, one of which entails him moving faster than the speed of light, as he was nowhere to be found before, during or after the incident and he vigorously denied being in the vicinity. Nevertheless, we have since confirmed that he "bumped" the wall. Sorry about all the brouhaha. However, we are engineers and we aggressively tackle problems, especially ones that hint at structural failures in our very old home. :)
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I'm glad that there was a rational explanation! What sort of engineer are you?
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OK, so the rod, which I assume was both painted and nailed to the load bearing wall, was in contact with the thin wood panel. Picture I assume was hung using a nail put through the panel, and into the rail as well. Probably what happened is the end of the rail where the panel is, had a fracture of the glue bond that hel d it to the wall. This breaking of the bond pulled down on the picture nail, probably breaking it off in the panel as well, but imparting an upward force as a jerk on the painting suspension string. This then went up, and cleared the obstacle and went sailing to it's final position.
the breaking of the glue bond energy was imparted to the thin board, turning it into a large resonant panel and transferring this energy into sound in the air. The remainder of the rail, now having lost the load bearing ability of the panel section, now went into stress well past design load, and eventually this caused more glue bonds to fracture, and then the mass of the clothes on the unsupported section cause a brittle fracture of the rail at some point, and probably the elastic energy of the supported section was enough on the release to break it off the wall in most measure. If you had looked in the room pre failure it is likely you would have seen a section of rail broken free at the panel side, and deflected down from the load till it failed.
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Maybe it wasn't your son, maybe the rod was bent in an arch shape and this arch suddenly reversed (hence the noise) causing a force to be imparted into the wall thus propelling your picture across the room, and due to the rod now being in a sagged reverse arch could no longer sustain the load and then collapsed.... Your sons innocent and you now need to buy him a new bike ;)