SuperStockAndy Posted December 5, 2011 Posted December 5, 2011 What if you made a model weigh its scale weight? For instance, a '69 Z/28 Camaro weighs 3765 lbs. When you divide that by 25 (1/25 scale), you get 150.6 lbs. Is that right? It just seems stupidly heavy for a model.
JamesW Posted December 5, 2011 Posted December 5, 2011 Maybe heavy for a model, but if it were built out of actual steel, aluminum and all the other metals, plus the weight of all the fluids it would probably come close.
B-dub Posted December 5, 2011 Posted December 5, 2011 I can't see a 1:25 model being close to 150lb even if it was made out of all metal..
Junkman Posted December 5, 2011 Posted December 5, 2011 It's a bit more complicated. weight, being proportional to volume, scales as the cube of length. If typical lengths on the actual car are 25 times the model lengths, then its weight will be 253= 15,625 times the model's weight. In other words, the correct 1:25 scale weight of a 3765 lbs Camaro would be ca. 0.25 lbs.
Maindrian Pace Posted December 5, 2011 Posted December 5, 2011 It doesn't work that way. A 1:18 diecast doesn't weigh 200 lbs, does it? -MJS
SuperStockAndy Posted December 5, 2011 Author Posted December 5, 2011 I didn't know it was so complicated.......
JamesW Posted December 5, 2011 Posted December 5, 2011 It's a bit more complicated. weight, being proportional to volume, scales as the cube of length. If typical lengths on the actual car are 25 times the model lengths, then its weight will be 253= 15,625 times the model's weight. In other words, the correct 1:25 scale weight of a 3765 lbs Camaro would be ca. 0.25 lbs. It doesn't work that way. A 1:18 diecast doesn't weigh 200 lbs, does it? -MJS I thought about that AFTER I replied. lol
Aaronw Posted December 5, 2011 Posted December 5, 2011 (edited) Think about volume. A 25 foot truck is only 12" (1 foot) in 1/25, but while any single measurement is a linear 1/25 reduction, the volume / weight has to take into account that all three dimensions are shrinking. A 1/25 5.0 liter engine is not a 0.2 (5 divided by 25) liter engine it is a 0.00032 liter engine (5 divided by 25x25x25 or 15625) because it is 1/25 of three dimensions. A 0.2 liter engine would be like a small weed wacker motor or large RC airplane motor. Edited December 5, 2011 by Aaronw
Foxer Posted December 5, 2011 Posted December 5, 2011 (edited) Aaron has the right idea. Say the 1/25 Camaro that weighs 3765 lbs is 7" x 3" wide x 2" tall (from the rocker sills up). this is simplified, but close enough and I don't have a Camaro to measure. The volume is 7 x3x 2 = 42 cubic inches. If you assumed the same density as steel (.28 lb/cu in) it would weigh .28 x 42 = 11.7 lb. This is off because the 1:1 car is not all steel and is not proper scaling . Scaling the previous assumed dimensions up gives 175 inches long by 75" wide by 50" long = 656,250 cu in for the 1:1 car. The overall density would be 3727 divided by 656,250 = .0057 lb/ci. This seems small, but steel is .28 lb/ci.and a car is mostly air using only the outside volume. When scaling it is assumed the density of the material remains the same. This gives .0057 x 42 cu in = .24 lb. for the scale Camaro. I'm a Structural Engineer and would be interested on any takers to disprove this. Of course, It does assume the scale model is made from all the same materials as the 1:1 car. Scaling the material density would be unrealistic in my opinion. Edited December 5, 2011 by Foxer
Junkman Posted December 5, 2011 Posted December 5, 2011 Aaron has the right idea. Say the 1/25 Camaro that weighs 3765 lbs is 7" x 3" wide x 2" tall (from the rocker sills up). this is simplified, but close enough and I don't have a Camaro to measure. The volume is 7 x3x 2 = 42 cubic inches. If you assumed the same density as steel (.28 lb/cu in) it would weigh .28 x 42 = 11.7 lb. This is off because the 1:1 car is not all steel and is not proper scaling . Scaling the previous assumed dimensions up gives 175 inches long by 75" wide by 50" long = 656,250 cu in for the 1:1 car. The overall density would be 3727 divided by 656,250 = .0057 lb/ci. This seems small, but steel is .28 lb/ci.and a car is mostly air using only the outside volume. When scaling it is assumed the density of the material remains the same. This gives .0057 x 42 cu in = .24 lb. for the scale Camaro. I'm a Structural Engineer and would be interested on any takers to disprove this. Of course, It does assume the scale model is made from all the same materials as the 1:1 car. Scaling the material density would be unrealistic in my opinion. The exact result with my formula is 0.24096 lbs, so I'd consider it close enough. I have a Ph.D. in physics, if that counts for anything, and I say you are correct.
Aaronw Posted December 5, 2011 Posted December 5, 2011 The exact result with my formula is 0.24096 lbs, so I'd consider it close enough. I have a Ph.D. in physics, if that counts for anything, and I say you are correct. No I am sorry but you only took it to 5 decimal places, it is sloppy work like that, that is ruining kits.
Junkman Posted December 5, 2011 Posted December 5, 2011 (edited) No I am sorry but you only took it to 5 decimal places, it is sloppy work like that, that is ruining kits. Add the weight of the Dixie flag decal on the roof and the entire calculation is out of the window. Edited December 5, 2011 by Junkman
Harry P. Posted December 5, 2011 Posted December 5, 2011 ok, I'm confused. Say I have a square block of steel, one cubic foot (1 ft. x 1 ft. x 1 ft.) and let's say for the sake of argument that it weighs 25 pounds. Are you saying that if I had a smaller block of steel exactly 1/25 the size of the bigger one, that it wouldn't weigh 1 pound?
SuperStockAndy Posted December 5, 2011 Author Posted December 5, 2011 ok, I'm confused. Say I have a square block of steel, one cubic foot (1 ft. x 1 ft. x 1 ft.) and let's say for the sake of argument that it weighs 25 pounds. Are you saying that if I had a smaller block of steel exactly 1/25 the size of the bigger one, that it wouldn't weigh 1 pound? Yes, that's what's confusing me also. I'm under the influence that perhaps it's how tight the molecules are joined, maybe?
Agent G Posted December 5, 2011 Posted December 5, 2011 There's a whole lot of variables involved in this. The actual material involved, size, and volume are the major players. We once used a formula similar to Foxer to achieve the scale weight of a Sherman tank. The real deal mikes in at roughly 35 tons, logic concludes the 1/35th scale tank would weigh 1 TON. It doesn't, scale weight would be on the order of 24-25 pounds. Now you tell me how I can get that plastic model to weigh 25 lbs.? Maybe I could add enough of something to fill the voids, but what? Now if I accurately replicated the scale tank in like material, steel, steel, rubber, and more steel, I think I'd get there. G
Junkman Posted December 5, 2011 Posted December 5, 2011 ok, I'm confused. Say I have a square block of steel, one cubic foot (1 ft. x 1 ft. x 1 ft.) and let's say for the sake of argument that it weighs 25 pounds. Are you saying that if I had a smaller block of steel exactly 1/25 the size of the bigger one, that it wouldn't weigh 1 pound? Correct. It wouldn't weigh 1 pound. It would weigh (1/25th ft x 1/25th ft x 1/25th ft) x 25 pounds. And that's 0.0016 pounds. For more realistic figures: A cu ft of steel really weighs 490 pounds. A cube 1/25th it's size would be 0.48 in x 0.48 in x 0.48 in. A cube with less than half an inch edge length doesn't weigh 1/25th x 490 pounds, i.e. 19.6 pounds. It weighs (1/25th ft x 1/25th ft x 1/25th ft) x 490 pounds. And that's 0.03 pounds, roughly 14 grams.
SuperStockAndy Posted December 5, 2011 Author Posted December 5, 2011 Now you tell me how I can get that plastic model to weigh 25 lbs.? Maybe I could add enough of something to fill the voids, but what? Now if I accurately replicated the scale tank in like material, steel, steel, rubber, and more steel, I think I'd get there. Yeah, that's assuming that the model is made out of ALL the same materials as the 1:1.
Harry P. Posted December 5, 2011 Posted December 5, 2011 Correct. It wouldn't weigh 1 pound. It would weigh (1/25th ft x 1/25th ft x 1/25th ft) x 25 pounds. And that's 0.0016 pounds. For more realistic figures: A cu ft of steel really weighs 490 pounds. A cube 1/25th it's size would be 0.48 in x 0.48 in x 0.48 in. A cube with less than half an inch edge length doesn't weigh 1/25th x 490 pounds, i.e. 19.6 pounds. It weighs (1/25th ft x 1/25th ft x 1/25th ft) x 490 pounds. And that's 0.03 pounds, roughly 14 grams. Wow... that's so counter intuitive. Not arguing with you... I just find it hard to get the concept that 1/25 of the original does not weigh 1/25 of the original. So if a gallon of water weighs 8 pounds (just a guess)... don't 10 gallons weigh 80 pounds and vice versa?
Harry P. Posted December 5, 2011 Posted December 5, 2011 ok, I think I get it. Volume is three-dimensional, not two-dimensional.
SuperStockAndy Posted December 5, 2011 Author Posted December 5, 2011 ok, I think I get it. Volume is three-dimensional, not two-dimensional. I don't. This is waaaaaaay beyond my knowledge
Junkman Posted December 5, 2011 Posted December 5, 2011 There's a whole lot of variables involved in this. The actual material involved, size, and volume are the major players. We once used a formula similar to Foxer to achieve the scale weight of a Sherman tank. The real deal mikes in at roughly 35 tons, logic concludes the 1/35th scale tank would weigh 1 TON. It doesn't, scale weight would be on the order of 24-25 pounds. Now you tell me how I can get that plastic model to weigh 25 lbs.? Maybe I could add enough of something to fill the voids, but what? Now if I accurately replicated the scale tank in like material, steel, steel, rubber, and more steel, I think I'd get there. G There are no variables whatsoever. If the real tank weighs 35 metric tons, it's scale weight in 1/35 is 0.81 kg or 1.78 lbs if you prefer old money.
Tony T Posted December 5, 2011 Posted December 5, 2011 That is directly proportional, Harry...scale dimensions are linear. Yes, counter-intuitive, for sure, but physics wins!
Harry P. Posted December 5, 2011 Posted December 5, 2011 When I joined this forum I was told there would be no math...
SuperStockAndy Posted December 5, 2011 Author Posted December 5, 2011 When I joined this forum I was told there would be no math... I wish that was the truth...
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