# COMMUNITY

### How to Tell if a Webpage Sucks

Somewhat amusing: How to Tell if a Webpage Sucks.And yeah, we try not to suck. If we accidentally do you should tell us. :-)

Posted by canida 10 years ago

### Teaching Middle School Through Instructables

I am a junior high math and shop/technology teacher. For years I have been wanting to develop a math program that uses as much hands on as possible.  Like all teachers, I have developed a few projects, but just don't have the time to develop all the activities needed to cover an entire curriculum. I would love to correspond/collaborate with others (including non teachers). Email me directly if you are interested.  mikemckay@pwsd76.ab.ca

Posted by mikemckay 6 years ago

### Trailer (from old truck) Differential can Seize?

Do i recall correctly? Can the wheels seize up because of an issue with the differential?

Posted by Toga_Dan 3 years ago

### Knex differential

I created the differentials a while ago. Larger versions are possible without any modifications of the basic pieces. This version is designed to be smaller in diameter than the main drive gear, requiring a modification to that gear.

Posted by Speed8ump 10 years ago

### differential amplifier tech

Hello, I'm following a circuit diagram for a current monitor that uses an op-amp as a differential amplifier. Connected to V- and V+ on the amp are the positive and negative leads of a 10mH Inductor that senses the current (as much as 9A) passing through an insulated positive line. The gain on the op amp, I'm told, is 220. If I calculated this correctly then at 9 amps in the insulated wire, 0.09V should be produced by the inductor and there upon entering the V+ lead and -0.09V in the V- lead for a differential of 0.18V which gets amplified to 39.6V. However the voltage source that powers the op amp is only 9V. So question # 1: Did I break down the math correctly? question #2: What happens to the excess voltage from the gain? I am getting all of my op amp information from wikipedia. I've never used an op amp successfully before.

Posted by watchingmachine 11 years ago

### Motor assisted pedal powered rail rider

I am trying to build a 2 person human powered Vehicle that is also motor assisted, I need a way 2 people can pedal at diffrent speeds and drive the same axle. What I think I need is some sort of differential gearbox. What Ii need to know is: Is there is a differential that can take 2 different input speeds and have one output? If it did and I also pushed it with a motor would the wheels spinning feed back though the gearbox and send the pedals spinning like crazy? Any help or advice people can offer would be great.

Posted by BillP55 8 months ago

### Peltier-element: Limiting its heat by tapping the power?

Hi I have a question based upon logics and the function of a peltier-element. we all know, that you can supply power to a peltier-element to raise the temperature on it one side and lowering it on the other. So it increases the differential. Now: If we heat the "cool" side and try to radiate the heat off the hot side (eg cooling it a bit), we can get a small amount of energy off the peltier as electrical current. The current depends on the temperature-differential: The bigger the more. OK so far. Nothing new. But what made me think was the fact, that you have 2 opposite states: Heat Side C and cool side H --> Get energy out in proportion of heat-differential. Put energy in --> Side C gets cooler and side H gets hotter in proportion of energy supplyed. By getting energy OFF the peltier, you in some way, redirect some parts of the heating-energy to the electrical-output. Also that is nothing new and we all know that since energy cannot be generated but only converted (in our case from thermal energy to electrical energy). Now what puzzles me is: Does it actually affect the temperature (-differential) of the peltier, if you get energy off it? Lets imagine the following experiment: - You build something like in https://www.instructables.com/id/Candle-Powered-Electric-Candle/ - Now you disconnect the load (lamp) and measure the temperature on the upper side (Away from the candle). - Wait for a steady-state when the upper side doesn't get hotter - Now turn on the lamp thus redirecting a bit of energy away from the peltier. - measure the temperature again on the upper side. Does it lower the upper temperature a bit? of course it wont be lower than the unheated state. But lets say the steady state was 55°C. Would it be like 50°C if i switch on the lamp?

Posted by Orngrimm 5 years ago

### Why is that little solar panel sneaking about...

That little solar panel that popped up behind robot, it was a link before but now it's in a sensible place...  Actually it was a little advertising easter egg earlier but now it's sitting there in its rightful place all smug and whatnot, lording it over me like some kind of photovoltaic fuhrer, thinks he's so good with his ability to turn photons in to voltage differentials, like I can't do that when I try.

Posted by killerjackalope 7 years ago

### What can you tell me about Stirling engines?

I'm interested in using a Stirling engine in a solar energy project. From reading around and doing some numbers it looks like I'll need around 1.5 kilowatts, and something in the vicinity of 30% efficiency or upwards would be nice, though I realise this may be overly optimistic. So, what's available, how much will it cost, what temperature differential is ideal, how big and heavy are these things, etc. Any info I get would enormously helpful. Cheers, Daniel.

Posted by SolarFlower_org 9 years ago

### Led Clock, Need Help. Using Arduino

I want to make a clock where there is a led blue or clear marking each hour around a circle, the led is on for that hour and then moves to the next led in the circle for the next hour.  pretty simple.  it will look kind of like an analog clock except without the hands.  for the minutes, i want the same leds as the hours to light up but since there will only be twelve, it will only be accurate within 5 minutes.  the minutes need to light up less bright that the hours so that i can differentiate between the two.  I have an arduino uno, breadboard, resistors and leds.  Please Help!!!

Posted by earthswater 6 years ago

### Feature Request: Repeat Ible Alert

Sometimes I see a new Instructable (usually by a first-time poster) that is very nearly a repeat of an existing Instructable. I think that if people knew that their idea had already been I'bled before they published it, many of them would stop at that point (which would be unfortunate) but SOME of them would make the extra effort to differentiate their work with some new or novel approach, or better directions/photos/results, etc. If you do a "view Instructable>>" while you're building one, the "Related" sidebar of similar Ibles shows up, but it doesn't appear to be intelligent at that point. That might be a simple fix. Or maybe as soon as you fill in the "Name This Instructable" box, the "Related" sidebar would appear. Just a thought. James

Posted by Scubabubba 9 years ago

### bikeframe to trikeframe

Hi all, ok here is my plan, any advice is welcome and appreciated. I am not building a bike frame, however I am converting a bikeframe into a trikeframe. The first image attatched is a bike i have that i have stripped down to the frame, seat and bars. the second image shows a hudson carrier trike from the 1930s. So i want the bike i have to have a chassis like the hudson carrier. i plan to have a differential encorporated into the chassis. Does anyone have any ideas about building the chassis: which type of metal? where to get metal from in UK, weather using an existing chassis and encorpating it into the existing frame is good; possibilities, ideas, suggestions any discussion is welcome, thanks for reading my post!!! Nicky

Posted by nickyrai 10 years ago

### Potential \$5 RC Hovercraft

Hey y'all, I was bored, so I made this RC hovercraft, kinda like a Tiny Whoov, from the guts of a \$5 RC helicopter (sold at most FiveBelows). The idea is that a hovercraft is more fun than a cruddy helicopter, in addition to being a fun and easy DIY project for the weekend. It could be a nice gift to a kid. My first concern was that the motors would not provide enough power to get the thing moving. They give more than enough power, and this thing can MOVE. My second concern is that the differential thrust steering system (one motor turns faster than the other, steering the hovercraft) would not be effective enough. This is still a problem that I don't have the enthusiasm or time to solve anymore. Maybe someone could figure out how to reprogram the FC board to have more differential thrust (is that possible?), or somehow configure a servo or actuator without raising the cost of materials too much. Anyway, here's the concept, go have fun with it.Supplies:Foam platesHot glue\$5 RC helicopter with 2 motors and receiver (LED optional, but really cool)Connector (the battery might be soldered directly to the FC board, so this will make it easier to fiddle with)Soldering iron (not %100 necessary, but it can come in handy)Propellers (see design notes)Design notes:Notice how the underside of the hull is curved and smooth. I used propellers from a Blade Inductrix FPV Pro, but any micro quad propellers should work. Notice the nice little compartment under the FC board where you can stick a battery without the need for Velcro or glue. This would be a very easy FPV mod, but that would add about \$20 to the cost.

Posted by Thorondor95 5 months ago

### MGS5's iDroid - Can it be Built with Open Source Tech?

I can't get enough of Metal Gear Solid 5! It definitely deserves the 10/10 scores its received! But as cool as it would be to have a giant robot or even a Walker Gear that you and/or your enemies can pilot, I think the coolest thing to have from the game would be the "iDroid". If you havent played "The Phantom Pain" or "Ground Zeroes", the iDroid is a device Snake uses for multiple purposes. Some include: sending radio trasmissions and calling in supply drops or helicopters between the iDroid's location and Mother Base, Displaying a topographical satellite view of the area Snake is in, Organizing Mother Base staff, resources, R&D; projects, and playing music from cassette tapes found while on missions, Just to name a few. (bold font is to differentiate the uses) So is it possible to build a similar device using the open source technology of today? (minus the use of cassette tapes and a 2D holographic projection screen) I'm pretty confident that it can be done, but what do you guys think?

Posted by EngineerJakit 2 years ago

### MGS5's iDroid - Can it be Built with Open Source Tech?

I can't get enough of Metal Gear Solid 5! It definitely deserves the 10/10 scores its received! But as cool as it would be to have a giant robot or even a Walker Gear that you and/or your enemies can pilot, I think the coolest thing to have from the game would be the "iDroid". If you havent played "The Phantom Pain" or "Ground Zeroes", the iDroid is a device Snake uses for multiple purposes. Some include: sending radio trasmissions and calling in supply drops or helicopters between the iDroid's location and Mother Base, Displaying a topographical satellite view of the area Snake is in, Organizing Mother Base staff, resources, R&D; projects, and playing music from cassette tapes found while on missions, Just to name a few. (bold font is to differentiate the uses) So is it possible to build a similar device using the open source technology of today? (minus the use of cassette tapes and a 2D holographic projection screen) I'm pretty confident that it can be done, but what do you guys think? (btw i also have the same topic in the Tech section, cuz i figured that would fit well probably)

Posted by EngineerJakit 2 years ago

### Sound Locator Circuit?

Hey all, Here's an idea maybe one of you solder-jockeys can help me out with: Ever have a sound that you'd like to find the source of, but your ears can't tell you where it's coming from?  I'd like to build a circuit to do that. I was thinking of something like three electret microphones with op-amps between them in differential mode.  That would give three signals that would be, presumably, the ratio of sound coming from each mic.  (And, therefore, an indication of direction.) Of course, I'd also like to get an adjustable bandpass filter in there somewhere to isolate just the sound I'm looking for.  That's the part that complicates all designs I've thought of. And then, if I could somehow figure out distance too, that would be the ULTIMATE! Here's one possible use case: A car makes a funny squeal noise a highway speeds. The mechanic takes out this device and magnets it inside the hood.  He runs a control wire back to the cabin. Once the car is in motion and making the desire noise, he adjusts the BP filter using potentiometer(s) and a pair of headphones. The device tells him where (relative to itsself) the sound is coming from. Your bill is less because the problem was diagnosed quickly without a lot of guesswork. Thoughts?

Posted by PS118 8 months ago

### Just 24 more hours..

And this week is over.. I'm about to whine about life, so back out now if you like. What a hell of a week, I started going to UCF monday. Now, admittedly, I'm happy about that, even though it's terribly stressful. But that's not the problem, really. No, would you believe that monday I bit into a brownie at work and cracked a molar on a nut? So my first day of school was accompanied by horrible pain. Followed by a dental crown on tuesday. Yeah that's not that bad, so I'll add in that my wife's truck needed a new differential on thursday (somewhat more expensive than a calculus book). And today?The washing machine broke. Spent three hours tearing it down, it's a goner. Leaking pump, with horrible grinding noise, broken balance strut, and no power to the motor. Only six years old too. And worst of all i didn't win the explicative deleted bike. That's an almost \$2500 outlay this week for broken things.. Oh yeah one more really irritating thing, I finished up my A.A. and received my diploma this week, in a big flat envelope stamped all over "Do not bend", which the mailman folded in half and stuffed in the mailbox. I'll probably read this in the morning and decide I'm a self absorbed SOB and delete it. ;-)

Posted by Tool Using Animal 10 years ago

### Speed Cameras

Posted by trebuchet03 10 years ago

### Mathematics

In one of my classes, it was necessary to review Laplace transformations. I realized that, after many months of not using it, I had become extremely rusty in integration by parts. Once I saw the basic idea, it slowly came back to me. Therefore, and I know the core audience isn't exactly appropriate, I would like to do a series of math related instructables AND I would like to have one or two collaborators. There's a few reasons I'm doing this.... 1. I feel the internets lack a resource with basic instructions of advanced mathematics (there's a few good resources, but it's mighty hard to find a "how do I do this" sort of thing). 2. Teaching is a great way to refresh the memory 3. The potential of comment feedback could be a good indication on what else should be covered. 4. Perhaps earlier basic introduction is useful to someone? Or not.... 5. The focus, in addition to how, is why such things are done. You won't find that on wikipedia :p Some topics to include (not necessarily individual projects) - and the projects would be something like How to solve _____. Basic definitions - notation Differentiation Integration Fundamental theorem of calculus Chain Rule Separation of Variables Integration by Parts ODE's Laplace transform Fourier Transform Anyone interested in collaborating - even on one subject? Then, anyone interested in looking at these? Not necessarily to learn how, but to see why it's done? For the why/application - I mean given a real world scenario... I promise, the application portions won't be boring (at least not for the nerdy type) ;)

Posted by trebuchet03 10 years ago

### Electric Power Generation and Resistance Questions

Okay so I understand the basic concepts of power generation but I have a question pertaining to the old addage: An object in motion tends to stay in motion. Resistance is power that stops any said object if it is equal to the energy of the object in motion - this resistance is from gravity and other outside forces acting upon said object. OKAY If the force to put an object in motion was then then collected by electrical generators from multiple other sources as part of the same object - would it be able to make up for the amount of resistance from the added collection and the amount needed to put said object into motion and keeping it in motion???? If an object is designed to be in motion then it does not require as much energy to stay in motion as it does to be put in motion. Even when affected by gravity, as it is affected by gravity less when is in motion. But can technology (bearings and rotors) be designed so they offer less resistance than the amount of energy required to keep said object in motion? This is impossible as far as I am aware. Energy is NOT free - but If the energy required to keep an object in motion is less than required to put it into motion, would not the true energy of the object in motion be greater than what is required to keep it in motion and be able to be collected as excess energy? Collection would result in resistance however and since the formula of "greater or equal force" applies collecting anything other than that differential in energy would result in the objects motion being slowed. Is this true? I am concerned about going into details on the nature of my concept until I can gain a better understanding of the science behind it. As such I apologize for how vague my questioning is.

Posted by Tetsuoh 2 years ago

### toy rc car steering mod

I just got a sorta good used R/C toy car for \$2, pretty nice for \$2, and it works too full suspension, differential drive, two speed gearbox, and the steering mechanism uses a servo but this servo has all of it's control electronics out side the gearbox and on the single PCB the car uses. I just want to hack it so that I can turn it into a 2.4ghz (freebie RF modules from cypress yay) controlled "hobby grade" car with variable speed and such this gearbox has 7 wires sticking out of it, 2 are to power the motor itself, another 2 is 6v+ and ground ( - ), the last three is a potentiometer in the mega ohms range, higher than 20 mega ohms for sure, because it goes out of my multimeter's range if it's at neutral, but goes to about 10 mega ohms when the wheels are turned now, my datasheet for my PICmicro says in the A/D converter section "The maximum recommended impedance for analog sources is 2.5 kÃÂ©" I can't really replace the potentiometer inside the gearbox, there is room for me to fit in my own, what would you do? *add parallel resistors to the potentiometer (probably easiest) *I can have a piece of paper shaded from light to dark and have a photo resistor tell me the darkness of the paper (might get jerky) *I can probably directly attach a potentiometer outside the gearbox directly in line with the output shaft (durability issues) *or I can put a gear on the shaft and have a potentiometer above the gearbox (I would need to cut my chassis to fit it) what sounds good?

Posted by frank26080115 11 years ago

### Using TEC chips and heatsinks for personal cooling - heating collars or pads

I've been toying with using TEC chips (facinating devices that are cheap - applying voltage make one side hot - the other cold, Inversely, appling any existing temprature differential to the sinks PRODUCES POWER). They are used most commonly by consumers in auto beverage coolers and heaters. It  started when a car ran me down on my bike, and I was wearing a neck brace for months. I thought about how misserable I'd be if it were summertime. I also thought of those poor people that always wore them... Anyway, there's a thousand different easy ways to do this - I took fluid-filled plastic sections of a beverage cooler and attached them to a belt, which hangs around my neck. applied the heat  sink of the TEC and there you go - just wrap it in something. Now if I were on a motorcycle in summer and stopped in traffic, the cool collar would be a lifesaver, as well as a myriad of other apps. I cannot figure out the best (inexpensive) way to control this. It's easy enough to turn on and off - you can hardly forget it! But if I allow the chip to get too much wattage it will get too hot and self-destruct. Also, if I limit the wattage correctly, it would just need adjusting, and could be left on most of the time. The idea here is there are many ways to do this but they are too expensive... I want everyone to be able to afford it. If you use a Pot or resistor, the excess goes to heat and ruins battery life, and other controllers of DC current are expensive. Any help? I am almost 60 and have earned the nickname Misc. Expert among my family and friends, and I must say I'm very impressed with what y'all do here in this newsletter - Congrats!

Posted by miscexpert 6 years ago

### audio / light frequency matched color organ

Hi there, this is my first time to the forum! I've been doing some searching, as I would like to build a colour organ but further differentiate b/w audio frequencies and the circuit they trigger. Bascially, I would like to take an audio signal (preferably from a mic) and use it to trigger lights based on musical notes. So basically, every A (...110 Hz, 220 Hz, 440 Hz...) would light up a certain circuit, and on for all 12 notes of the musical scale. Of course, I would not limit the response to only 440 Hz for example but slide it to the edge of the adjacent notes' frequency, with 440 Hz occupying the median. So, I'm wondering what components are necessary to make this happen. In a recent DIY project I saw there is rough split between 3 frequency ranges (bass, mid, treble). If I were to approach it with the same design concept, I would need (8 octaves for example, at 12 notes each) 96 different circuits to run. I'm not opposed to using a PC with some kind of digital signal processing to take the place of these circuits. Also, I want to run the lights on 120 V power for non-LED lights. My experience in circuit building is nil, but I've consulted circuitry diagrams before for other reasons, so I'm not totally green. I'm computer savvy but only to a certain extent. Not much programming experience save for a 1st year university course. I have an analog to digital convertor, but that's it for components.  Once I have the digital signal in, where do I go from there?  I'm assuming I will need some kind of software to convert via fourier transform to a frequency domain signal then filter all the frequency ranges from there.  I assume I would have a digital out signal to a switching circuit board with 12 outs to control the power supply to the lights.  Can anyone point me in the right direction?  Many thanks!! HQ

Posted by H.Q. Tinwhistle 6 years ago

### router bypass (/w toggle switch)

Hello, it's been a while. This problem requires someone with IT experience, and basic wiring. (the two go hand-in-hand really.) An ethernet cable is made up of 8 color-coded cables. the colors are brown, brown-white, blue, blue-white, orange, orange-white, green, and green-white.(for ease of coloring, I didn't differentiate between the mixed/solid wires) The principle works similar to that of a lag switch. The solid orange cable handles the data flow, and in lag switches it is "cut" by a  simple on/off switch. But here, Instead of the solid orange cable being "cut" by the switch, it simply switches the input. Hence the toggle switch.  **I realise you can do the same thing with port forwarding, but however hard I try, it does not work. Even software made to do it won't let me. Before i go out and by 4 ethernet cables that i don't need, i was wondering if this concept would work. From the modem out, the ethernet cable is spliced into two wires, which had two paths: path 1: directly to the router, out a router port and to the switch (red line picture 2) path 2: directly to the switch. (red line picture 3) from the switch, the cable goes directly into the computer tower. with a simple flick of the switch,  the input to the switch would either go through or bypass the router. although the green and blue current (amps) is split, the amperage is joined again at the switch because of Kirchoff's current (?) law. although the orange is split, it cannot flow through both wires at the same time because one will not have any place to flow. because the internal wires are twisted to reduce interference, I would use the required minimum of 2 feet for any segment. Q1: would this work? Q2: if so, would this effect the router because the power is split.  Q3: if so, would an 8-pole toggle switch be the solution? Q4: would this have any negative effects with the power going moving at different rates (destructive interference) Q5: would an alternate setup be more plausible? (see picture 4) Thanks in advance -Pyro

Posted by ich bin ein pyro 7 years ago

### A Quest!

OK - first off, hello everyone!! I've not posted an Instructable for perhaps 4 years now, but I have done a fair few things in the intervening time (shortened life story to follow - if you just want details about the project, scroll down.) Not sure when, but in early childhood I started playing around with K'NEX. I'm sure you'll all agree thats acceptable for a kid of about 5. Several years progressed before I discovered the art of K'NEX weaponry - which led me to create my first ever (and widely crap) Instructable. My fascination for things that you have to put together to make them work has not faded - I have become involved heavily in the Greenpower Race Series for Schools (www.greenpower.co.uk, if anyone's interested - I'm Rob on the forum) and next year will probably be my last truly competitive one - I'm building the one for next year over the summer. Having looked for a couple months about what I can do next, I've come up with a bit of a foolhardy quest  that sevearl people have probably already done. The Project (hello, if you've just scrolled down) is to design, build and drive on the road an Electric, 2-seater, Hardtop Sports car with the following features: 85 MPH top speed (15 more than the Motorway limit), 500 mile range, flash charging capabilities, various mod-cons (e.g. a windscreen), some luggage spaces and a price tag of as little as possible. I'm probably going to be designing the chassis on a 3D CAD program (either Solidworks or AutoCAD) over the next couple of years, as well as getting enough money, sourcing parts, and designing the PWM (Pulse Width Modulation, controls how long the motor is on for in any given second) system. Here is a list of what I see as I need to do: Source electric motor Source batteries + charging system Design chassis Source parts for chassis - Welder, rear differential, steering components, bits of Aluminium/Steel (haven't decided which) box/tube. Build rolling chassis. Anyhow, I will be making an instrucable and will hopefully publish it once I'm done. The whole thing will consist of my entire design process and building processes. Everything from chassis stress testing to choosing what type of dials to have. Hope that was mostly interesting! Rob Hopeful Instructabler

Posted by Blue_Flame 7 years ago

### Contests vs. Challenges - what the what??

Posted by scoochmaroo 6 years ago

### What is a wavefunction?

In the Physics topic on the EPR paradox, NachoMahma asked about wavefunctions and "collapse."Let's put aside the whole "collapse" issue -- not all physicists agree that it is a sensible concept. NM's comment has a link to the Measurement Problem, and I'm not a good enough theorist or philsopher to contribute to that argument.What is the wavefunction? "Is wavefunction only a convenient way to say it's located somewhere close to here, but we're not sure exactly where until we measure it?""At any particular point in time/space the object is in a definite spot with a definite set of properties, but we can only make a reasonable guess?"No. The wavefunction, spread out over all of space (I'm speaking non-relativistically here, but the formal interpretation applies to spacetime), is the fundamental "thing" in QM. "Objects" are wavefunctions. If the wavefunction is localized (non-zero for a small contiguous set of coordinates, zero everywhere else) then treating it like a particle makes sense. Otherwise, it doesn't; the thing behaves like a wave, showing diffraction, interference, and lots of other effects. My preference, when I talk about these things, is to just call them "quanta." They are not particles, they are not waves; they are their own kind of entity with well defined, if really hard to understand, behaviour.How do I get to that point? Well, quantum mechanics is one example of a "field theory" (electromagnetism is the most familiar classical field theory). The equations we write down (the Schrödinger equation non-relativisitically, the relativistic Dirac and Klein-Gordon equations) to describe how quanta behave are coupled partial differential equations (PDEs), which relate the values (and derivatives) of the field at every point in space to their evolution in time.A PDE which relates the time and spatial properties of a function is either a wave equation (if the solutions are sines and cosines) or a diffusion equation (if the solutions are exponentials). The Schrödinger equation is a wave equation, and we call the solutions wavefunctions. Electromagnetism also has a wave equation, which is how we get radio, light, etc.The difference is that the functions in EM are "real valued:" the value of the field at each point in space/time is a regular floating-point number (the "phase" in EM is determined by the relative values of the field and nearby points). The wavefunction is a '''complex valued''' field -- at each point in space/time, the field has both an amplitude and a phase (or equivalently a real and an imaginary component). This means that wavefunctions can interfere in ways more complex than simply "adding" or "subtracting", which can have quite interesting consequences.You get probabilities by taking the square (norm) of the wavefunction. This procedure gives you a real value, a probability, at each coordinate. When you make a measurement, those probabilities determine which coordinate value you see as the "location" of the quantum. The actual result is random, but that isn't because "we're not sure exactly." The quantum objective does not have a single coordinate location until we make the measurement.How that happens, whether by "collapse," "decoherence," "many worlds splitting" or something else, is a subject of intense philosophical and experimental argument.

Posted by kelseymh 9 years ago

### Why or why not does .9 repeating equal 1?

I already posted this as a regular question, but someone told me to make it as a burning question, so here it is: HI! I am wondering if .999...=1? I mean if 1/3=.333 and 1/3+1/3+1/3=3/3 and 3/3=1. So wouldn't .333...+.333...+.333...=1? But it actually equals .999... not 1. I googled this question and I got many different answers ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For example...(someone wrote): I'm not really into math, but a friend brought something up to me today that really seemed very strange. (For the duration of this post, .999 will mean .9 repeating unless otherwise specified- just for the sake of ease) .999=x 10x=9.999 10x - x = 9x 9x=9 1x=1. .999 = 1. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Someone else wrote: Numbers are fake. They are a manifestation of our minds to describe something, similar to words. Just because we say "red" doesn't mean something is red. what is red? Languages and math are very similar. Math is universal...at least for our planet though. .999~ does not = 1. But what .999~ repeating represents, does in fact equal what 1 represents. No-one will ever be able to comprehend infinity, os its time to stop trying. Think of space and the universe. IT IS GROWING. how can it continue to grow with no stop? what is there to contain it? WE need something to contain it in order for us to understand it. We need a stopping point, but there is none. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Another person wrote: In your proof that .333...*3=.999... you forgot to include the fact that .3333... is NOT 1/3. 1/3 if not a number that can be turned into a decimal in any way. I thought someone might like to know this fact. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ And the last person wrote: Just a pedantic point the equation for differentiation is given by lim x->0 [f(x+h)-f(x)]/h, it has the minus sign. It is after all just telling you the slope and is no different really from doing simple trig using the tan function. Here you just take a really small triangle. As to the 0.99~ thing, this is really just writing the supremum (spelling might be off) of the numbers less than 1. Just think of it as taking the smallest number 'n-word' than 0 away from 1. They are not identical for if they were we would not have a continuous number line, but rather a dashed one with lots of wholes in it. I could simply argue that 0.99~8 is just as close to 0.99~9 as 0.99~ is to 1. For those who really want to understand go and look up supremum numbers and the axioms of the real number line. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ So who is correct? Do you agree that .999...=1? Or .999... does not equal 1?

Posted by Pizzapie500 8 years ago