Wikipedia:Reference desk/Archives/Science/2013 June 9

= June 9 =

how the measurement in a dc potentiometer is being done??
how the unknown resistance is measured in a dc potentiometer? — Preceding unsigned comment added by 112.79.43.96 (talk) 03:47, 9 June 2013 (UTC)
 * Do the Wikipedia articles Potentiometer (measuring instrument) or Ohmmeter help? -- Jayron  32  04:25, 9 June 2013 (UTC)


 * You can use a potentiometer as part of a Wheatstone bridge in order to measure an unknown resistance. Red Act (talk) 05:27, 9 June 2013 (UTC)

Surveillance camera disruption
What thing can disrupt a surveillance camera other that an electromagnetic pulse and a fake footage? 76.88.39.179 (talk) 04:33, 9 June 2013 (UTC)
 * Shine a laser into the lens. Looie496 (talk) 04:44, 9 June 2013 (UTC)


 * Obstructing the lens? Disconnecting it? Moving it so it points in the wrong direction? I'm sure there are many other ways... AndyTheGrump (talk) 04:45, 9 June 2013 (UTC)


 * Solid state sensors CCTV's will suffer 'snow' in high radiation environments, e.g., within nuclear reactors. Volcanic gases can contain hydrofluoric acid. That really messes them up. 10 year old Homo sapiens armed with only curiosity and screw drivers render surveillance cameras completely defenceless. Maybe the OP would like to narrow down his question.--Aspro (talk) 13:16, 9 June 2013 (UTC)


 * Hang a piece of nylon that moves, then she will take 24 hours Picture, thanks water nosfim --81.218.91.170 (talk) 11:29, 10 June 2013 (UTC)

--81.218.91.170 (talk) 04:52, 12 June 2013 (UTC)

F1=ma=mg=F2 or a=g
Why all objects in free fall have the same gravitational acceleration “g” when diverse masses (say from lightest to heaviest) require unlike forces to move the same distance and can be inferred in the Newton’s 2nd law of motion which states “The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object” i.e. a= F/m. So my question is when F1=ma=mg=F2 or a=g then why not a=g in the following example?

Example:

An acceleration of 4m/s/s is produced if a net 20N force “F1” is applied to block of mass of 5kg F1=ma; a=F/m=20/5=4m/s/s.

A constant gravitational acceleration of g=9.8 m/s/s is NOT produced by the same magnitude of 20N gravitational force”F2” if acted on free fall mass of 5kg F1 =ma=mg=F2=20=5x9.8 (Not congruent)

Shouldn't F1and F2 be dead on before making substitution/ elimination for a=g?74.200.19.65 (talk) 04:33, 9 June 2013 (UTC)Eclectic Eccentric Kamikaze
 * The magnitude of the acceleration of gravity is always the same. The magnitude of the force is the object's weight and is different for objects of different mass. a is always g in the absence of other forces (at least near the Earth's surface). In your case, your force is about 49 N for a 5 kg object.--Jasper Deng (talk) 04:37, 9 June 2013 (UTC)
 * Why would F1 = F2 when you're using different accelerations in your calculations? Your accelerations are different (4 m/s/s vs. 9.8 m/s/s), so the forces necessary to produce that acceleration will also be different; It won't be a 20N force acting on the object in free fall.  -- Jayron  32  04:45, 9 June 2013 (UTC)


 * The gravitational force between two objects (one of which happens to be a planet) is proportional to the product of the two masses. So a heavy object has more gravitational force applied to it than a lighter object.  But acceleration is proportional to the force divided by the mass - so even though heavy objects have more force applied to them, they accelerate at exactly the same rate as lighter objects.  When you're talking about acceleration, the mass elegantly cancels out and everything falls at the same rate. SteveBaker (talk) 02:02, 10 June 2013 (UTC)

What type of turtle
What type of turtle is this? At first my wife thought it was a Diamondback terrapin but now doesn't know. Bubba73 You talkin' to me? 04:53, 9 June 2013 (UTC)


 * Hard to tell. Maybe a slider of some sort, possibly a pond slider?  -- Jayron  32  04:57, 9 June 2013 (UTC)


 * I can give photos of the front and bottom if that will help. This is in coastal Georgia, about a kilometer from a salt marsh.  We've had moderately heavy rain.  Bubba73 You talkin' to me? 05:05, 9 June 2013 (UTC)


 * I'm going to guess river cooter. Unfortunately our article doesn't have a picture, but Google Image finds lots of them. Looie496 (talk) 05:31, 9 June 2013 (UTC)


 * This website is a good resource, he looks like some of them on that list, including the river cooter, and the map turtle, although those maps don't show them in brackish waters. It might be a worthwhile list of candidates though. Shadowjams (talk) 16:35, 9 June 2013 (UTC)


 * Thanks, looking at the photos at that website, I think it is a Florida Cooter. Bubba73 You talkin' to me? 18:09, 9 June 2013 (UTC)


 * A turtle expert identified it as a Yellow-bellied slider, a sub species of pond slider mentioned above. Bubba73 You talkin' to me? 14:36, 10 June 2013 (UTC)

I broke my soldering gun
I bought a cheap Am-Tech soldering gun and broke it by having it on for too long (I subsequently bought a Weller which came with instructions detailing its duty cycle which the cheap gun did not). Here is a photograph of the inside of the broken cheap soldering gun. Does that brown stuff suggest exactly what happened? Can I do anything with that chunk of metal? --78.144.192.116 (talk) 16:30, 9 June 2013 (UTC)
 * Donate the whole thing to your nearest recycling center. ←Baseball Bugs What's up, Doc? carrots→ 20:08, 9 June 2013 (UTC)
 * From the look of things, the transformer in your soldering gun overheated, melting the wire insulation in the windings. That brown stain is the melted resin, glue, or insulation, leaked out to the edges of the coil.  When insulation between the windings melts, separate wires in the coil short together, potentially rendering the entire transformer as a short-circuit (or at least a less-effective transformer, depending on the short).  It's also possible that the short blew the fuse, but the photo is too blurry to be sure.  Nimur (talk) 21:37, 9 June 2013 (UTC)
 * Dude, Looks like your fuse is blown on that S1735! If so, bum a fuse somewhere. If it works, party on till it melts down again! If not, I'd pack everything up real neat like in the cheap grey case it came in then shit can the whole kit and kaboodle. 184.242.31.141 (talk) 22:02, 9 June 2013 (UTC)
 * 184.242.31.141, are you honestly expecting anyone to believe that you can visually identify the make and model of a generic soldering-gun based only on a blurry photo of a disassembled unit? And if the fuse did blow, it indicates that the device drew too much current.  Replacing the fuse may temporarily restore functionality to it, but it will not solve the root-cause of the problem.Nimur (talk) 22:26, 9 June 2013 (UTC)
 * Man, I'm telling you thats a S1735. They suck right out of the box, it's like they were invented to break down.  Fortunately my trash compactor ate mine, but before it did, I was a fuse bummin bandit.  Amtech makes some happenin solder, but they ain't got the brains to make nothing good to melt it with. 184.199.165.229 (talk) 22:32, 9 June 2013 (UTC)
 * The above user is a troll. Pay him no never-mind. ←Baseball Bugs What's up, Doc? carrots→ 22:47, 9 June 2013 (UTC)
 * I think I should point out that the "fuse" is actually a light bulb (so that the user can tell when the gun is switched on). There may be a (non-replaceable) thermal fuse inside the transformer. Tevildo (talk) 18:44, 10 June 2013 (UTC)
 * The OP said it was an Am-Tech, and the picture the OP gave does indeed look like an S1735. Red Act (talk) 23:12, 10 June 2013 (UTC)

A special type of CRT?
The display on my intercom/video door phone is black and white, flickering and slightly bend (the top is closer to the front/viewer than the lower part of the display). The image is distorted if I move the receiver close to the screen, which I believe indicates that it is distorted by the magnetic field from the receiver. I understand how a regular CRT TV works, but I think the screen is too large (ca. 8 cm diagonal) for the depth (ca. 3 cm) of the device. Also this would not explain why the display is bend. So I was wondering whether in my case the electron beam is running in front of the screen vertically upwards. Since the screen is bend it could still hit different points on the screen requiring very little deflection (which is an advantage) in that direction. Not sure whether there is enough space for coils or condensator plates to achieve deflection in the other direction. So my questions is: Do I have a special type of CRT where the beam is running in front of the screen, or is it something else? bamse (talk) 20:56, 9 June 2013 (UTC)


 * Its condenser is on its way out. Replace.--Aspro (talk) 22:14, 9 June 2013 (UTC)


 * It would be easier to figure this out if you told us the make and model of the device. Walmart sells a Swann door phone that seems to match your description and uses a CRT screen. Looie496 (talk) 22:21, 9 June 2013 (UTC)


 * See also TV80 (and here's a photo and diagram of the CRT) --catslash (talk) 22:48, 9 June 2013 (UTC)
 * Thanks for the replies. @Aspro: Not sure what you mean, as far as I can see nothing is broken with it. It is designed this way. @Looie496: It is an older (15 years or so) commax, but can't see any model number on it. The Swann which you linked claims to be both a CRT and an LCD according to the description. @Catslash: That looks a lot like what I suspect. Only difference would be that the "Phosphor screen" is bend in my case, so one could perhaps get rid of the electric field between phosphor screen and "transparent thin oxide electrode". Not sure why a "Fresnel lens" is required here. bamse (talk) 15:05, 10 June 2013 (UTC)

what motor oil do i use for a 2001 bmw 740i with 159k miles in good condition? and other BMW questions
What kind of motor oil should i use on my BMW 740i? how do i get a manual for my car? What do i need to look at if the check engine light is on? And how do i open the glove compartment if the key won't work? How do i check the fluids? Are there any good diy fyi faq and how to guides that are free online? And also general owner's maintenance checklist and how to guide and videos? — Preceding unsigned comment added by 66.87.71.250 (talk) 23:12, 9 June 2013 (UTC)


 * You can always download a manual as a PDF file from . Plasmic Physics (talk) 23:48, 9 June 2013 (UTC)

Too many questions! Let's break it down so that our experts can answer by the numbers: SteveBaker (talk) 01:56, 10 June 2013 (UTC)
 * 1) What kind of motor oil should i use on my  BMW 740i?
 * 2) How do i get a manual for my car?
 * 3) What do i need to look at if the check engine light is on?
 * 4) And how do i open the glove compartment if the key won't work?
 * 5) How do i check the fluids?
 * 6) Are there any good diy fyi faq and how to guides that are free online?
 * 7) And also general owner's maintenance checklist and how to guide and videos?


 * I would suggest that getting a copy of the Owner's manual is the critical thing. It will certainly tell you what grade of oil to use, and how to check the fluids.  Bad fluid levels could easily cause the check-engine light - and certainly that's what I'd check first.  If the glove compartment has a lock - it's possible that the car was re-keyed at some time in the past and they didn't bother to re-key the glove compartment.  That's kinda unfortunate, because that's probably where the owner's manual is!


 * So either you need to get a locksmith to pick the lock on the glovebox - or you need to force it open. Probably that gets you the owners' manual - and from that, most of your other questions will be answered.


 * If by any chance the owner's manual isn't in there - you can find them on eBay all the time for under $20. SteveBaker (talk) 01:56, 10 June 2013 (UTC)


 * Or you can one for free, from the link I gave. Plasmic Physics (talk) 01:58, 10 June 2013 (UTC)


 * In some cars the entire glovebox assembly can be removed, then unlocked from the inside. I have no idea if it is possible in your car, but the procedure would be given in a service manual that you can buy at an auto parts store. The store should also be able to plug in their diagnostic scanner to see what is making the check engine light come on and give you advice on what it means. 209.131.76.183 (talk) 11:37, 10 June 2013 (UTC)