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Why does a van der Graff generator repel a stack of tin foil plates one at a time?
because the "inside" plates have no charge (they are in a Faraday cage made by the top plate and the VDG), but the top plate has the same charge as the VDG so is repelled, the next sheet then becomes the top one and so on. Mr Sparky
Show how Archimedes principle may be derived from concepts of fluid pressure?
Consider an object being immersed through a height h in a fluid. The pressure at the surface is smaller than the pressure at the bottom of the object. This difference in pressure, Dp, is given by: Dp = hdg where d is the density of the fluid and g is the acceleration of free- fall Now, Dp can be expanded as the ratio of force to area. So: F/A = hdg where F is the force exerted on the body and A is the bottom area of the object => F = Ahdg => F = Vdg since Ah = volume V => F = mfg where mf is the mass of fluid in the volume V ( mf = dV from the definition of density) => F = Weight of fluid displaced (shown) The force F is the upthurst on the body.
When a gas filled balloon rises up how can it be proved that it gains both Kinetic and Potential Energy?
when da balun rises up, upthrust V*D*g must b more tham weight mg m=mass of balun V= volume f balun,ie,volume of air displaced by da balun D=DENNSITY OF AIR d=density of gas in balun net force on balun=VDg-mg =(m/d)*D*g-mg Force=m*acclertion =mg{D/d-1) so acc=g(D/d-1) so WHILE RISING, KE WILL INCREASE N PE WL ALSO INCRESE BCZ HEIGHT IS INCREASING
What kind of belt do you use to make a van de graaff generator?
* Grey neoprene rubber (hard to find!) * Neoprene-covered cloth * Balloon rubber (use big balloons from a party store) * "Dynaband" exercize belt, made of rubber in various colors * Spandex cloth * "Dental Dam" latex rubber from dental suppliers, see the yellow pages. Certain other (ahem) specialty stores have dental dam rubber or even large latex sheets. Try McMaster-Carr #8611K11 Latex Sheet 0.006 inch thick. Try sporting goods stores for "Theraband" latex bandage. * "incontinence sheet", rubber bed sheet. Try a "surgical supply" store. * Cut up some disposable latex (thin brown rubber) gloves. Use cyanoacrylate (crazy glue) to make your belt. * Large rubber bands (or normal rubber bands, if your VDG is extremely small,) or other brown, gum-rubber sheets. * Glue: use rubber cement, or the strong glue which is supplied with bicycle tire-patch kits. Crazy glue is suppose to work too. * Yellow sign-tape from hardware stores, the kind that says "wet paint." The more impressive VDG will have yellow tape that reads "POLICE LINE" or "CRIME SCENE" ! (From Archie Mcphee, http://www.mcphee.com) * Polyethelene garbage bags, cut crosswise into belt-like strips * Urethane industrial belts. N. Simmons reports that these can be ordered in custom sizes from Pyramid, Inc., Newton, IA, phone 515-792-2405 Make sure they understand that you want NO kind of antistatic coating or additives in the belt material. * Another source is http://www.durabelt.com * People on the PHYS-L discussion list recommend spandex cloth, with the ends of the belt bonded with crazy glue. If you're building a VDG from scratch, take a look at my TRIBOELECTRIC SERIES page. This will give you hints about materials to try as the belt and the roller. A polyethelene roller used with a rubber belt is traditional, but I doubt it is the ultimate combination. Rubber belts can be made from rubber strips glued end-to-end. Rubber cement will work OK. Much better is the glue used in innertube tire repair kits (bicycle shops have this.) Note that this glue has toxic fumes and probably shouldn't be used by kids except with adult supervision. I've heard that cyanoacrylate "crazy glue" works well, but have not tried it myself yet. If you use a thick material, it helps to eliminate the glued lump: before gluing, "feather" the ends by filing or sanding the material into a taper. If done perfectly, a glued tapered joint will have no lump at all. Another hint: cut the ends of the strip diagonally, so the glue joint will be a diagonal stripe across your belt. Then instead of going "thump-thump-thump" over the rollers, the glue joint will make a smooth quiet sweep. I have it in my head to try freezing the rubber in dry ice w/alcohol, or liquid nitrogen, and then grinding with a belt sander, but I don't know if this will actually work. Very thin belt material doesn't require feathering, but it's less sturdy. Belts made of thin balloon-rubber have a limited lifetime because the ozone and nitrides being generated by the corona-combs will attack the rubber chemically, making it brittle so it becomes full of holes. If possible, avoid black rubber or brightly-colored rubber because sometimes the coloring makes the rubber conductive. To test for this, on a low-humidity day try rubbing your belt material on hair, fur, etc. Hairy arms do nicely. If it becomes charged and will attract the hair, the material is OK. If it will not charge up, either the material is conductive and the excess charge leaks away, or the air is too humid and your test is spoiled because *everything* is slightly conductive from the adsorbed surface water. How to test the air humidity? Try rubbing a balloon on your arm hair and check for attraction. If rubbing a balloon doesn't electrify its surface and make hair rise, the weather is too humid, so therefor you cannot easily test your belt material. There are a couple of companies which sell VDG replacement belts for various classroom generators:
Who invented the first tandy color computer?
The first 'Tandy Color Computer' was referred to as the 'Radio Shack Color Computer'. It wasn't until near the end of the second version of the color computer (There were three in total) that the name was changed to the 'Tandy Color Computer 2'. The first version, as with the others, was developed by the Tandy Corporation (parent company of Radio Shack). The original color computer used the Motorola MC6809E microprocessor as the primary CPU, MC6847 VDG (Video Display Chip), The MC6883 SAM (Synchronous Address Multiplexer), and two Peripheral Interface Adapter chips (for Input/Output). That, plus RAM and ROM comprised the heart of the machine. The original machine came with 4k of RAM and 8k of ROM (color basic). Ultimately, Tandy released an extension to color basic (extended color basic), bringing the ROM to 16k, and RAM upgrades to 16, 32, and ultimately 64k. The original color computer had the standard 'Tandy Gray' color and a 'calulator style' 'chicklet' keyboard. The final revisions of the first color computer did convert to a white case. The next version of the color computer was functionally identical to the first in nearly every respect, and had an improved, but still flat keyboard, which was eventually changed to a full travel keyboard. The internal workings were improved, but retained the same basic chip layout for CPU, Video, SAM, and PIA. The last computer in the line was the Tandy color computer 3, which added 4 keyboard keys (control, alt, F1, and F2), and much of the internal workings were condensed to a single chip. The Video and Address chips were condensed to a single Chip (GIME)or 65424 Chip. This chip emulated all supported modes of the original machines, but left out some upsupported, (but non the less sometimes used) 'semi graphics' modes. It did however increase the resolution and color set over the older systems. By the end of life cycle of the color computer, it had a huge following which lives on today in a small, but active vintage community and emulators, but by the early 90's, it was clear that the majority of the market was going the PC compatilble route, and the color computer 3 was discontinued.
