The Thing

Thanks calbiterol. For the project I'm handing in I'll just build a magnetic gauss rifle, instead of the automatic, because I don't think I'll have enough time for it. However, I will make the automatic Gauss rifle! Probably during spring break, summer, or some other long weekend. I have lots of 3 meter long square lumbers (like the sticks for holding up signposts and stuff) lying around my school's wood shop and I can cut a section using the table saw and dig a groove in it using the milling machine, then work on the electromagnetic one! Thanks for the help!

... OMG OMG Thanks 5614. Arrrg I need to go shoot myself. EDIT: Crap, missed.

I want to create a circuit that dims or brightens a LED. I want the LED to glow BRIGHTLY as the environment around it gets darker, and vice versa. I know I have to use a photovoltaic cell and maybe transistors, but the exact wiring of this circuit escapes me. I will probably also use a separate power source for the LED, but maybe not. Help please!

@ flyboy: That's a coil gun, and I've decided against building one of those. Now I'm building a Gauss rifle. Thanks for the link though. I've seen your design on the electromagnetic gauss gun paint ball shooter thing that you were discussing with D22k, calbiterol. However, I have just about 4 or 5 days to build this thing before handing it in, and how much time would it take to wrap about 100 electromagnets? They're too weak - I only have a maximum power source of 9V batteries.

Thanks. Could you explain to me how the returning mechanism will work? I will probably cut the length of the wood to 1m, and the magnets I have are not TOO powerful. They're for hanging hand tools, yes, but I don't think they're the N40 bone-breaking ones. EDIT: Incidentally, can I build a smaller scale gauss rifle? Like everything's smaller so smaller magnets, smaller ball bearings, and build it minature scale? Oh yeah, and please explain how the returning mechanism works. As I said above. Thanks!

Yea I've thought of that too . I thought of a manual one, so each magnet will have a little thin plate sticking out behind it. So when the ball hits the plate, the energy will be transferred, but I can have a handle on the side and I'll pull it back using manual force. Is that what you're suggesting as well? Our teacher would not let us use anything above 12V . She's scared of caps, so AC's definitely out of the question. Incidentally, are there any other electronic add ins or just plain addins to add to my rifle to make it fancier?

That's a good idea, and I've thought about it. However, how can I make the electromagnets as strong, if not stronger, as a neodymium magnet? That's what I'm worrying about, because I DON'T think I'll have an AC supply.

Well, thanks everybody. I've decided against the coil gun because our teacher absolutely refuses to allow me to have even a few hundred volts built up across the circuit. So, I'm just gonna do a much safer Gauss Rifle! Basically its a bunch of magnets spaced out on a wooden stick (120 cm in my case, yea!), and 2 steel balls in front of each magnet. When a steel ball is attracted to the first magnet, it will transfer its energy, push the 2nd steel ball in front of the magnet, which will hit the magnet in front of it, and transfer its energy, and so on, so the device is accelerating and at last, the final steel ball will burst through the muzzle. Any tips for making this way-too-simple-to-hand-in rifle more advanced and fancy? Like adding some further electronic functions? Also, I can't see this thing being rapid fired, cuz each steel ball requires moving back to the magnet by hand.

What happened to the ferrofluid that didn't get any spiking? Did it only show blobs? What magnets did you use trying to get it spike? Yea I found that site. However, where do I get some kerosene from? Thanks.

Does anyone know how to make a passable to good quality ferrofluid (magnetorheological fluid (sp?))? I know of the crude iron filling to vegetable oil method, but I've heard that it doesn't work. Are there better methods? Thanks.

Hi all. I am considering making a rapid-firing coil gun for a school project. NO it will not be a gigantic man-slaughtering weapon of mass destruction - I doubt whether it will even break the sound barrier (more like dropping like a stone after travelling 2 feet). Honestly, I'm happy if I get the projectile out a meter before it hits the ground. So, can anyone suggest some ideas or plans or sites to help me? I've googled around, but they all are either camera flash cap powered or gigantic cap more than capable to kill a person powered. And they're all one shot, then wait for the cap to recharge style. Are there any rapid fire ones? I saw a few movies of a very low power but rapidfiring coilgun. It was awesome. So, should I go around messing with caps? One thing is certain, a cap-powered coilgun will NOT give me rapid firing abilities. So, should I build a slow-firing cap coilgun, or a rapid firing battery coil gun? I am leaning towards the latter, but then, where can I get a 12v battery with an appreciable amount of current? So, help and ideas please?

How did you get it copyrighted? What happened then? Did I do the exact same thing as you did?

Err...they're supposed to work in degrees... Why are they invalid?

Wow. I believe I've just come up with a new formula for pi. I don't think it's been done before, but just in case, I'll show you and you guys can comment on it: A circle is essentially a polygon with an infinite number of sides, and so pi would equal the perimeter of the polygon / 2r. If we set the r to 1, then pi = Perimeter/2. The perimeter of an equilaterial polygon is side length * number of sides. How do we find the side length? Well, we drop two lines from the center of the polygon so that the two lines form an isosceles triangle with the length of one side. To find the topmost angle of this isosceles triangle, we divide 360 degrees by the number of sides, to get the topmost angle of this triangle. (360/x), if x is the number of sides. To find the two base angles of the isosceles, subtract the topmost angle from 180 and divide by two, so we have (180-(360/x))/2, which can be simplified to (90-(360/2x)) Now we can use either the sine law or cosine law. Using the sine law, we find the length of 1 side of this polygon is: (remember the radius is 1, thus the two sides are 1) 1/sin(90-(360/2x))=s/sin(360/x), thus s=(sin(360/x))/(sin(90-(360/2x))) Using the cosine law, we can see that s=sqrt(1^2+1^2-2*1*1*cos(360/x)), simplifying: sqrt(2-2cos(360/x)). Now we multiply the number of sides (x) by the length of the sides and divide by the diameter of 2: (xsin(360/x))/(2sin(90-(360/2x))), and (x*sqrt(2-2cos(360/x)))/2 So we can account for when x approaches infinity by using a limit of these functions: lim x-->infinity ((xsin(360/x))/(2sin(90-(360/2x))))=pi lim x-->infinity ((x*sqrt(2-2cos(360/x)))/2)=pi We can also reduce the bottom of the first formula, so get a third limit: lim x-->infinity ((xsin(360/x))/2)=pi Well, here's a method (well, 3) for calculating pi using simple trig!

Yea, but my aim isn't to stop it. Frankly, how many times does a bridge collapse? Once only, so one shine per crystal would suit the purpose. If a bridge's deformed or about to collapse, I'm not aiming to reinforce it to make it hang on. Saving lives sounds pretty good to me . Now, say we have this crystal, and if say when the stress is critical or when the bridge undergoes hysteresis or other material failure signs, the crystal will shine. We can have an oscilloscope attached to it just for experimental purposes. However, where on the bridge would this crystal be placed to detect the material failure? That's what I'm wondering... And also help for the experiment and which alkali halide to use?

Would that be hysteresis, which is usually a precursor of material failure? Hmm... the bridge collapse detection experiment is forming... So, for the experiment, I can attempt to crush a crystal and record the photon emissions using an oscilloscope (would I need a photomultiplier?)

Thanks swansont. Triboluminescence yielded a lot more results. I've seen the lifesaver experiment, but it was bitten, not crushed with a hammer =). Can there be any value to this property? As far as I know, only asymetric crysal structures exhibit this behavior (?). Can it be used, say, to tell when a bridge is about to give? Or even for lighting maybe? I'm thinking of doing an experiment on the former possibility. What equipments should I use? An oscilloscope? Thanks a lot.

What is mechanoluminescence? I've searched around the internet but all I found were research and experiment ON it, and nothing that explains about it. So what is it? Also, I am hoping to do an experiment regarding mechanoluminescence for a school project and I think I will have access to an oscilloscope. What is a good experiment? Thanks a lot.

Try googling "Make Flash Pre-loader". There are a gazillion tutorials floating around on this.

I remember seeing this experiment before. It was with soap before I think. It was a Whys Guy experiment.

Thanks cosine. Incidentally, I wrote a very simple program just to show how one can calculate pi simply by using a polygon. No it's not Archimedes's way, I think its simpler. All it requires is a knowledge of the sine law. Unfortunately, the programming language, VB, uses floating point decimals to store my large data and as the number of sides a polygon has approaches the trillions, it becomes too inaccurate. Cosine, where can I find info about the convergence and the efficiency comparisons of different methods?

Huh? Oh, no, this won't be my REAL science fair. It's just something to show to the teacher, so I actually HAVE something and not absolutely flunk the entire thing. The teacher, well, from my experiences with her, likes impressive sounding titles. I've worked with the teacher enough to know that she will DEFINITELY give anyone a good mark if the topic's impressive enough. Okay, with the time diminishing fast and furious, I've gotten an idea: gathering the existing methods to calculate pi and testing their efficiencies, as well as devising my own method using very simple geometry and trigonometry and a limit when x approaches infinity and testing IT.

This is one of the many reasons that one should use Firefox: StumbleUpon! I used StumbleUpon to stumble upon that site.

That's where I got it from lol. I was doing random searches on google when I found the article (the science fair summary). Never mind though, I'm not looking for it anymore. Incidentally, what ways have been devised to calculate pi besides the 4arctan(1/5)-arctan(1/239) one?

I've just saw an article online about finding a recursive expression for pi through a formula of centripetal force. It doesn't tell you how though! Anyone's ever heard of this?