chris Posted December 19, 2003 Report Posted December 19, 2003 My son asked me last night why CDs had round holes instead of just about any other shape that would conceivably be used to hold the disc more firmly. I figured I'd ask the most musically knowledgeable bunch I know It does seems like it would make more sense of the hole in the center were shaped like, say, a + sign or something... Quote
couw Posted December 19, 2003 Report Posted December 19, 2003 the holidays are coming up, people are starting to really have time for the questions their children ask them Quote
JSngry Posted December 19, 2003 Report Posted December 19, 2003 Does the CD spin, or is it the laser? If it's the former, then I think that answers the question. If not, then I don't know. Quote
Alexander Posted December 19, 2003 Report Posted December 19, 2003 Does the CD spin, or is it the laser? If it's the former, then I think that answers the question. If not, then I don't know. It's the former. Quote
chris Posted December 19, 2003 Author Report Posted December 19, 2003 Well, the CD certainly spins, but wouldn't it be a better "grip" if the hole had a shape other than circular? As my son said: you don't see screws with round slots for turning them Quote
John B Posted December 19, 2003 Report Posted December 19, 2003 Does the CD spin, or is it the laser? If it's the former, then I think that answers the question. If not, then I don't know. That sounds like a zen riddle. It is not the cd or the laser that spins, it is your mind. Quote
Dmitry Posted December 19, 2003 Report Posted December 19, 2003 In order to be read by the laser CD must rotate. It's makes more sense to rotate an object with a round center hole than the one with square hole. Less interferences, even spead of the rotational forces across the cd surface. Non-round hole would create an uneven path of rotation, methinks. Quote
couw Posted December 19, 2003 Report Posted December 19, 2003 and now someone please translate all that friction, interferences, rotational forces, and uneven paths of rotation talk into something a child may understand. Quote
chris Posted December 19, 2003 Author Report Posted December 19, 2003 I guess even if it were a symmetrical shape like a plus sign that still would potentially cause wobble? That makes sense. I tried to convince him it had to do with tolerance for even wear from the spindle (as in, if it started to wear, at least it would wear evenly so it wouldn't wobble), but I think he saw through my "dad has no idea, really" smokescreen. Too bad he's past the age of "because Dad said so"... However, I think I will spring the Zen koan on him first Quote
Dmitry Posted December 19, 2003 Report Posted December 19, 2003 and now someone please translate all that friction, interferences, rotational forces, and uneven paths of rotation talk into something a child may understand. A child will understand just fine. It the adults that might need assistance... The square pegs go into the square holes, and the round pegs go into the round holes. Fill a round mug 1/2 with water or a beverage of your choice, rotate the pencil inside. Chances are no water comes out the rim. Now do the same with a square mug. Water will splash outside. Helped? Quote
Alexander Posted December 19, 2003 Report Posted December 19, 2003 Well, the CD certainly spins, but wouldn't it be a better "grip" if the hole had a shape other than circular? As my son said: you don't see screws with round slots for turning them Have you ever had a problem with the CD flying out of the CD player? The round hole is fine! If it ain't broke... Quote
catesta Posted December 19, 2003 Report Posted December 19, 2003 Too bad he's past the age of "because Dad said so"... There is a certain age bracket for that? Dang....., I need to get my dad on the horn, he's got a lot of splaining to do. Quote
couw Posted December 19, 2003 Report Posted December 19, 2003 yup, helped. But WHAT does all this stirring of beverages have to do with CDs having round holes? Quote
Chrome Posted December 19, 2003 Report Posted December 19, 2003 And I always thought the holes were round so you could hold 'em on your finger when you fumbling with jewel cases, etc.! Quote
Dmitry Posted December 19, 2003 Report Posted December 19, 2003 yup, helped. But WHAT does all this stirring of beverages have to do with CDs having round holes? It's called a visual aide. Americans love those. Pie charts and all. You might also ask him to poke in his nose. Round finger in a round nostril gets the boogers out way better than a square one would. Of course if the boy is 15 and older you might want to use some other references. B) Quote
catesta Posted December 19, 2003 Report Posted December 19, 2003 Fill a round mug 1/2 with water or a beverage of your choice, rotate the pencil inside. Chances are no water comes out the rim. Now do the same with a square mug. Water will splash outside. Helped? D, I tried this with one of those coned paper dixie type water cooler cups, the friggin' pencil went right trough it. Quote
catesta Posted December 19, 2003 Report Posted December 19, 2003 You might also ask him to poke in his nose. Round finger in a round nostril gets the boogers out way better than a square one would. Of course if the boy is 15 and older you might want to use some other references. B) Quote
chris Posted December 19, 2003 Author Report Posted December 19, 2003 These are actually great explanations of why the CD iself is round, but not really of why the hole in the middle is round... the spindle grips the CD and doesn't move relative to the CD as the water in the round cup does. If the function of the hole in the middle is to give the mechanism something to hold onto when it spins, then the shape, as long as it is symmetrical on four major axes, is really immaterial, right-- it could be shaped like a + or an * -- the more corners there are, until it effectively becomes circular, the more tolerance there would be for error, I suppose. However, when it comes to having a gripping surface and providing a firm hold onto the disc, then shapes other than round would seem to be better-- or at least there would be no chance of slipping (which I guess isn't really a problem, but you know True, it isn't broken, so don't fix it... But really, I'm just trying to avoid going to work! Quote
couw Posted December 19, 2003 Report Posted December 19, 2003 You might also ask him to poke in his nose. Round finger in a round nostril gets the boogers out way better than a square one would. Of course if the boy is 15 and older you might want to use some other references. B) now, that's all nice and gross and stimulating in various ways, but the question remains: why are the nostrils round? - cause your fingers are too - so, why are the fingers round? - 'cause of the friction; to illustrate, imagine a glass of Wodka-Martini .... Somehow all this visual aide stuff is shite without a nice scary formula to go with it. Show them kids you still know something they don't! and end your short lecture, with "see, it's simple logic." Quote
patricia Posted December 19, 2003 Report Posted December 19, 2003 (edited) At the risk of sounding like a small, curious child [which isn't a bad idea], it seems to me that the design of the Robertson [square] or Phillips [star-shaped] would have more firmly connected the CD to the turney-thing on which it plays. However, unless you have a square or star-shaped finger, the fumbling would have been made more complicated, on the CD's trip from the jewelcase to the player. So, you would be solving a problem that really isn't a problem with one which would cause annoyance as CD's careened across rooms for lack of a convenient finger-hole. Speaking of nose-navigation, I'm reminded of an incident of just that. My daughter wasn't walking yet and was just about to perform some probing with her finger. I was sitting right beside her and frowned, telling her, "Don't put your finger in your nose!!" In a split second, she grabbed MY pinkie, with the intent of using it for the operation. Who says kids don't listen? Edited December 19, 2003 by patricia Quote
couw Posted December 19, 2003 Report Posted December 19, 2003 Wheel is the greatest invention of mankind. Followed by compounding of interest, self-adhesive postage stamps and fox news channel. I thought CDs were the greatest invention of man kind? I mean, what's this thread all about? Beverages? Quote
JSngry Posted December 19, 2003 Report Posted December 19, 2003 I thought the hole was round so's it would remind us of records... Quote
Dmitry Posted December 19, 2003 Report Posted December 19, 2003 I thought CDs were the greatest invention of man kind? I mean, what's this thread all about? Beverages? I think it's about unqualified adults taking on a task of explaining obvious things to children that would otherwise be better off figuring out those things on their own. Did anyone say beverage? Quote
couw Posted December 19, 2003 Report Posted December 19, 2003 (edited) Have one on me! (beverage that is) the clue does lie in beverages BTW, it would be infinitely more difficult to put a disk in Correctly when there is a polygon of any shape you have to fit your disk onto. With wobbly eye-sight and trembling hands, the operation is easiest when dealing with a round hole. There's one dimension less to deal with. prosit Edited December 19, 2003 by couw Quote
rockefeller center Posted December 19, 2003 Report Posted December 19, 2003 (edited) These are actually great explanations of why the CD iself is round, but not really of why the hole in the middle is round... the spindle grips the CD and doesn't move relative to the CD as the water in the round cup does. If the function of the hole in the middle is to give the mechanism something to hold onto when it spins, then the shape, as long as it is symmetrical on four major axes, is really immaterial, right-- it could be shaped like a + or an * -- the more corners there are, until it effectively becomes circular, the more tolerance there would be for error, I suppose. However, when it comes to having a gripping surface and providing a firm hold onto the disc, then shapes other than round would seem to be better-- or at least there would be no chance of slipping (which I guess isn't really a problem, but you know True, it isn't broken, so don't fix it... But really, I'm just trying to avoid going to work! If the whole in the middle was not round, you would have to place the CD in a certain angle relative to the spindle. Edited December 19, 2003 by rockefeller center Quote
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