Bonjour , Qui pourrait m'indiquer la marche à suivre pour utiliser cette équation avec Arduino, il s'agit de relever le débit d'un capteur analogique , je pensais utiliser cette équation pour afficher le débit sur le moniteur mais ça me donne des valeurs erronées  Voici l’équation du capteur y = -8E-05x2 + 0,0361x + 1 y est le debit capteur x est la tension en sortie du capteur

Question by patate64   |  last reply

### How to write equations in posts

Sorry if this question has been asked lots of times on the forums but I couldn't find any answers for it. How can I display equations is a nicer way then just Gp(s) = 1/(tau*s+1) I tried using codecogs latex equation editor which showed the equations in the editor but on the actual post nothing shows up.

Topic by Roboro   |  last reply

### Can you allow users to use mathjax to add nicely formatted equations?

Http://www.mathjax.org/ Users can use Latex-like formatting, such as $\sum_{i=1}^n \frac{1}{n}$. See http://math.stackexchange.com for example. Thanks, Joe

Topic by angler   |  last reply

Hey, I'm in of person who has a patch for a quadratic equation for a TI-84. Thank you!

Topic by math hater   |  last reply

### Physics equation for air displacement? Answered

I want to make a fan powered go-kart, is there a formula I can use to calculate the minimum amount of air displacement to make it move?

Question by A-Nony-Mus   |  last reply

### need equation to repulsing magnets

I would like to know the equation for the repulsing of magnets I have a science project due and can't find the equation the internet kind of goes around the bush. If you can answer this as soon as possible  please I really hate to turn it in late. So if you have ANY helping ideas search tittle above                                                -caleb griffin-mose

Question by awe80me_k1ng   |  last reply

### What is the equation to determine a coil's inductance? Answered

I have been looking for the equation to determine a coils inductance in henries, but I can't find it. I want the one that uses core diameter, wire thickness, and wire length to calculate it. (But I'll take any equation that will allow me to calculate it easily without test equipment) Could someone help me out?                                                                                                                                                         Thanks!

Question by transistorguy   |  last reply

I am planning out my first Instructable. It will be a bent (kerfed) plywood coffee table, There have been a growing number of projects out in the 'makeosphere,' where people are cutting slits or kerfs that go almost completely through a thicker piece of wood, allowing it to be easily bent. I am on a super-tight budget, and cannot afford to ruin my $22 sheet of plywood, so I was hoping that someone might be able to help me with some measurements for cutting the kerf-slits in the plywood. Here is the idea all sketched out. I need help with the measurements that are in bold. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * PROJECT DESCRIPTION: Materials: 1x | 4 ft. x 2 ft. 3/4 in birch plywood 2x | 3 ft. 5/8 in threaded metal rods 8x | flat washers 4x | standard nuts 4x | "end nuts" Steps: On the sheet of plywood, measure in X inches and mark X number of cross cut lines, X inches apart. Measure in 2 inches from each end of the board and draw a line. Measure in 2 inches each each side of the board, and draw another line. Drill out a 5/8 inch hold at all 4 of these crossed lines. Thread a standard nut onto each end of the threaded rod and screw it on 1-2 inches roughly, then slip a flat washer over the threaded rod. Bend each end of the board up to create almost 90 degree angles. Insert each end of the threaded rod into the holes, slip a flat washer over the threaded rod and screw on each of the four "end nuts." Use the standard nuts, and the end nuts to fine tune the bends into 90 degree angles. Flip the table over, and enjoy. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Stability is more important to me than curve radius. I don't know if spacing cuts close together for a small curve radius is more or less stable than placing the cuts further apart for a larger radius. I've never done this, but I have seen that there is an equation for this. I haven't been able to find the equation actually expressed, I've just heard that there is one. Does anyone know about this area of woodworking/physics? Topic by Dolmetscher007 | last reply ### How to mathematically prove that a/b/b = a/b^2? Answered Question by Wisaam | last reply ### "Knex War?" (The Math Bit) Hey guy! Sharir1701 here and I just want to start off by saying that I'm not back into Knex warfare, but I have something to show you. About a year and a half ago, I posted this forum topic. There I explained why, in my opinion, just adding more rubber bands to a gun will not actually produce an overall better gun (past a certain, low point). I'm not getting back into that discussion, but I simply wanted to share something regarding that. Don't ask me how or why (I don't know, myself), but a few days ago I suddenly remembered that old assumption I made. Being a perfectionist, I hate leaving things unfinished or unexplained (particularly math and physics related inquiries). Back when I posted that topic, I had little to no formal Physics knowledge, and the beginnings of an understanding in mathematics. Now, I have a much broader understanding, much more knowledge, and an ability to explain and evaluate what I once couldn't. Anyway, what I'm trying to say is, back then, I didn't have the tools to prove my claims. I firmly believed in them, but I couldn't confirm them. It's nothing complicated, but, like I said, just something I'd like to share. I also want to point out that, although I personally don't enjoy spending days upon days perfecting a little plastic mechanism for firing (mostly) non-aerodynamic plastic projectiles, anymore, there still is a warm spot in my heart for the craft I once loved. More to the point - this is a small article just showing something I did in a few minutes the other day, that helps me to better understand how a Knex gun works. I hope that in writing this, more people that are still building guns, will think about more accurately calculating certain things about their guns to help improve their performance and hopefully produce more efficient guns. The final note I have is that I'm about to show you equations, all of which can be plugged with real, measurable numbers, to calculate to a high degree of accuracy, the forces at play. This means you can actually calculate the most efficient layout for a gun, and also that in designing your next, you will be able to use these equations, and many others, to find optimal solutions to your problems. So, what's all this fuss about? Well, basically, I just proved with a few, painfully easy equations that my conjecture about the forces in a gun, working on the pin, is true. I'll just get to it: First, Hooke's Law states that the force necessary to change the length of a spring or a (tense) rubber band is F=K*dX, where F is the force, dX is the distance you want to change, and K is a constant number, that each rubber band (or spring) has. You can quite easily measure both of these. For rubber bands connected parallel to each other (assuming they are the same type of rubber band, which ever is your chosen standard), this equation becomes F=K*dX*N, where N is the number of rubber bands used. dX and K are both constant in the regards of the pull of a pin on a standard Knex pin gun. Therefor, the amount of force required to cock a pin (pull it back to it's full length) is linearly correlated to the number of bands you put on your gun. Next, if we examine Newton's equation of work and energy, W=dE=F*dX, where W is the work, dE is the change in energy in your system (input from an external force, i.e. your hand), F is the force applied along a length of movement, and dX is that length. Let us define the base position of the pin (not cocked, minimum tension on the rubber bands, fully in the barrel, etc.) as having 0 energy. This then means that the work applied to the pin by cocking it is equal to all the potential energy it has. From this, plugging in the force, we get Ep=K*(dX)^2*N. Let us assume a perfect world, where we neglect the effects of friction and air resistance, and assume all the momentum of the pin is transferred into the bullet as it fires (I will briefly mention in the end, why everything we're neglecting here just strengthens my claim in reality, but let's continue for now). After being released (in other words, shot), the maximum velocity the pin reaches right before the end of it's journey can be found using the equation for kinetic energy Ek=1/2*M*(Vmax)^2, using the fact that (again, neglecting energy wasted as heat due to friction) the energy is conserved, as no external force is working on the system, which then means that Ep,start=Ek,end => K*(dX)^2*N=1/2*M*(Vmax)^2 => Vmax = sqrt(2*K*(dX)^2/M) * sqrt(N). The first sqrt term in the final equation is all one big constant (again, K is the ratio associated with the rubber band, dX is the distance the pin travels, and M is the mass of the pin), meaning we can conclude that (C for constant) Vmax=C*sqrt(N). Finally, force applied by a moving, massive object can be calculated using Newton's second law, F=dP/dT (P is the pin's momentum, T is the time it takes for the pin to go from velocity Vmax to 0, transferring all it's energy into the gun and the bullet, but as I said, let us assume all of it goes into the bullet), or F=M*dV/dT (M, mass of the pin, dV is the difference in velocity, Vmax-0, which is simply Vmax. This is because P=M*V, which means dP=M*dV, ignoring relativity). So, F=M*C/dT*sqrt(N). The time varies slightly, but insignificantly, so let us assume it is a constant. So that's it. The force exerted by the pin on the bullet is some constant (calculatable, as mentioned and as shown), times the sqrt of N, the number of rubber bands on the gun. So there you go. Just a little something I did out of the blue the other day and thought I would share a proof of my conjecture from what feels like eons ago. I hope you enjoyed. Finally, I would like to tell you guys, perhaps as a little tease, since I'm not sure if I will ever upload it, but I have made 1 more gun after I stopped posting. I have already slightly teased about it in my user info. I guess I'll tell you guys what it is if I'm already posting something here again :) Possibly my most enjoyable, most well received, and quite innovative gun of all time? The REMPAR-2. I built the REMPAR-3 (I was also going to call it S5 when I thought about posting it). In a brief summary, it's a pump action, chambering (or bolt action as I and many others falsely used to call it), magazine fed rifle, that's only 5 layers thick all over, except one tiny area where it's 8 layers thick (1.5 extra on either side), as a reinforcement, not necessary if you use less rubber bands. Oh, actually, there's another small necessary area where it's 7 layers thick, but it's tiny and doesn't make the gun look bulky at all, and who cares. Plus, the one is around the pump, which looks quite natural, and the other is "disguised" as a detachable sight (not really detachable) that also looks fine. It also looked fairly good for a gun that I made, it used (if I remember correctly) a grand total of 0 broken pieces, which is a big accomplishment for me (the mag has some broken white rods, but fuck off), and it worked flawlessly, reaching ranges over 80ft and being able to go at 2-4 rounds per second, depending on your skill level with it. In other words, I could shoot 4rps; My girlfriend, with no experience or practice, could do 2rps, which says something about the gun's comfortability and ease of use in my opinion. It shot blue rods up to an accuracy of about 5x5cm (2x2in) over 30ft, which is amazing for a Knex gun, and it was truly super comfortable. It wasn't even long at all, which is saying a lot, looking at some other people's attempts at 5-wide pump actions (I may also be guilty of an attempt several years ago). Being quite short and only 5 wide, it is also quite light. I'm sorry, I just really liked this gun, I think it was truly my best creation ever (of course, the S3 is by far the most innovative gun I've made, but it's mostly a concept gun, not meant for real effectiveness). I may post it in the future, but I'll make no promises. I suppose I won't leave you guys completely hanging and take a picture of it. Oh yes, there's also a neat, fun little thing I did, originally because I saw no other option, but then I actually really loved it. I'm talking about the mag-lock. It locks automatically (there's a band on it, but it ripped a long time ago, so...) and the mag cannot fall out. Then you pull on it with your middle finger, similar to a trigger, and the mag just drops right out. Love it :) Topic by Sharir1701 | last reply ### How do i build a device to allow an input and it give a designated output (1015469=input and B2-1= output)? I work in a warehouse as a forklift operator. I deal with looking at a number on a container, then have to look up the number by going through several pages to find the corresponding isle and row to place the container. EX. ( Container has 1015469 on it. I have to find that number on a sheet then it will tell me to go to B2. Once I get to B2 I have to find that number on another sheet of paper that has the isles and rows so it can tell me if it goes in B2 section 1 for route 20 or in B2 section 2 for route 21. I need to make a device with large enough memory to hold several thousand 7 digit numbers and have each number reference me to the correct destination such as B2-1 or B2-2. I really need some help with this. I have basic electronics experience and a small amount of visual basics experience. I need this device asap to increase my productivity at work so I can step up my performance so as not to loose my job. The device just needs a simple 10 digit keypad to enter the numbers then an enter button and a clear button to be able to enter the next number. It would be even better if I could enter several numbers at once, maybe spaced by a comma, and get several output locations since sometimes I move several containers at once and each goes to a different location. Then I could figure the most effecient route in the warehouse. Any help with this would be highly appreciated. Thank you in advance for any help or advice you can give. Ps. It also needs to be easily updated as the numbers in the database will be frequently changed and updated. Question by J.Reynolds09 | last reply ### what is the EMF AND torque equation for BLDC motor? How to calculate BLDC equation paramaeters? Question by vickyraja | last reply ### equation to work out temperature rise please? Hello, I would like to create a transparent chilled micro studio space: this is to photograph insects (which won't move if the temperature is cold so I can take a photo without harming them). My *basic* idea is 2 cube tanks from plexiglass, one approx 30*30*30cm (the smaller, in which the insect sits) and the larger 50*50*50, 2 tubes between them in a one way system to let air cycle between them, the larger with lots of freezerblocks and an aquarium pump to circulate the cold air through the system. I'm after a sustainable temperature (for approx 1 hr) of 1-3 degrees C. The sides have to be clear to let light from the flashes through, and there's a special slot in area into which a lens will poke through into the smaller cube. It's all perfectly doable and would in all honesty be a godsend if I could get it working. The thing is... I don't have the foggiest idea if it'll be cold enough, ie stay at the 1-3 deg C for an hr with a bunch of freezer blocks and a pump. And before making it it'd be good to know that theoretically it should work. Before I embark, would anyone knowledgable about such things be able to do a 'back of an envelope' rough guesstimate of whether it's likely to work or to be a miserable failure? Many thanks!!! Topic by ingleslenobel | last reply ### What is/is there an equation to figure the speed a projectile travels, based on the PSI or force applied? Question by PKTraceur | last reply ### Is this the quadratic equation ... Y = X squared / 4P My girlfriend it telling me I'm wrong X and Y axis and P is focal. Answered Question by bazalaz | last reply ### Is there an equation to figure a set amount of PSI to a recognizable, or commonly used force measurement? What is/is there an equation to figure the speed a projectile travels, based on the PSI or force applied? What would this force be? k/h | fps | m/h | m/min. | k/min.| Question by PKTraceur | last reply ### what is the equation i should use to dilute 50% hydrogen peroxide into lower concentrations? Answered Hello, i just got some 50% hydrogen peroxide, from my local pharmacy because they were out of 35%, plus for some reason 50% is free. anyways, i want to know whats the equation for finding out how many ml's of water i need to use to dilute a solution toa certain amount, as i want to use the 50% peroxide to make 30% , 22% and 3% peroxide. now ive looked on google and i couldnt find a thing , and if i did by chance come across it, i didnt understand it. what i want to know is how much distilled water will it take to convert 100ml of 50% hydrogen peroxide to the above concentrations, or if possible, could someone please give me the equation for converting any concentraion to any, please! also, whoever answers my question and solved my problem entirely will get a best answr i promise!!! Question by oldmanbeefjerky | last reply ### I need a detailed method of doing, and double checking Algebraic Quadratic equations? Answered What I lacked in school, over 30 years ago, was a backbone to ask the teacher what he meant, but his hurried learn this style of teaching. What I need now, is something I have having trouble getting, even from any of the several books on the subject I have, that claim to make it simple: that is, I need both the methodology of doing the equations, and I need to know how and why they work, so I can work out when I have done something wrong. Question by Goodhart | last reply ### Do I subtract the voltage? So I was reading in my electronics for dummies book and it said there is about a 1.2 volt drop when using a standard LED. So, when calculating a resistor, with say a 9v battery, in my equation, do I make it R = (7.8 - 3) / 0.02 ? Instead of using 9v in my equation, do I have to subtract the voltage drop first?? Thanks! ~electricloser Topic by HavocRC | last reply ### Is it possible to make batch files take fractions into account? Answered When you put a command to evaluate and equation, like (2/3)+1, the answer would just appear as 1. Even when you put an equation like (2/3+1)*3, where the answer is an integer 5, the answer would come out as 3. Any idea how to make batch files calculate the fractions together with the integers? Question by Aosih | last reply ### if you mix sodium chlorate with nitric acid , would you get sodium nitrate and hydrogen chlorate? Question by wiebevandomburg.hotmail.com | last reply ### 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. Topic by kelseymh | last reply ### Torque to linear thrust through lead screw Hi,I am trying to figure out maximum linear force I can produce with an electric motor through use of lead screw and nut. I have come up with an equation which seems correct but resulting forces are way higher than my intuition believes is correct.I tackled the problem from the perspective of energies:F' * p = M/r * 2*π*rlinear force * thread pitch = torque / radius [M/r = force at radius] * circumference of lead screwF = 2*π*M/p * (1-k) //k stands for coefficient of friction between lead screw and nut)Radius falls out of equation, which seems fine as force is provided by torque, which is radius agnostic. I used a 7€ stepper for source of torque which can provide 0.42 Nm of torque and a lead screw with 8 mm pitch and 4 mm radius, I assumed 15% losses. My equation tells me that such system can provide 280 N of force, which seems wayyy too much for a cheap motor.I have attached a python code that calculates linear force in case it helpsCan someone tell me if my equation is either correct or flawed? Topic by ptkrf | last reply ### How to calculate torque required for transport motor? I'm planning on making my own Segway. My biggest design problem right now is my motors. I need to find the torque needed to move them. I'm thinking an equation like this would use the radius of the wheels, the mass of the rider, etc. How do I find the torque needed to move this Segway? Bonus points if you can point me to a place to get one of these motors. I don't want to spend more than$20 each for the 2 motors. Thanks.

Question by 4lifenerdfighter   |  last reply

### I need help explaining the shape of this nebula Answered

Http://www.esa.int/spaceinimages/Images/2014/10/Butterfly_death_throes This image is the "Butterfly Nebula". I'm having trouble understanding it's shape. According to the accompanying blurb, the shape indicates a "bipolar nebular, where fast-moving gas can escape more easily from the poles of the dying star than around its equator. This creates a lobed structure reminiscent of an hourglass, or, as in this case, a giant butterfly." But... why? Why can the gases escape more easily from the poles?  Why is it harder to escape at the equator? Surely, if it was blasting from the poles, we would see a more linear shape, long "beams" of material shooting out of each end?  This image looks to me as if material blasted away from the equator, but parallel to the poles, almost as if the two halves of the star's surface were peeled apart, like turning half an orange skin inside out. Anybody got a borderline high-school/university level explanation for the shape?

Question by Kiteman   |  last reply

### Which cell &amp; how many do I need??

I'm new to this whole electrical engineering thing. Thx to instructables, I got a crash course in LEDs & wiring them up. I need to make a prototype LED array. How do I determine the right size & qty of cells (9v, AA, etc.) needed to run an array for a decent amount of time for an end consumer? What's the equation for figuring this out? Will the Ohm's Law equation (which I'm new to) work for me here? Anyone's help would be greatly appreciated!

Topic by firesurfer   |  last reply

### wants more pictures before i can publish

I am trying to publish an instructable i have created about equations, naturally there are not many pictures to include as much of the stuff is text based. what should i do.

Topic by resistanceisfutileiflessthan1ohm   |  last reply

### i want my motors speed to be constant with the temperature via an equation, its a school project. help!? Answered

My project is to make a fan that will be constant (speed) with the temperature of the surrounding, display the temperature on an lcd screen and have a servo tilt it up and down. I have made my code for now and it seems correct, i think my problem is with the clarity of my code or the power. lcd + motor + servo = aprox 15 volts, i use the aruinos 5v connected from my laptop to power the lcd screen and i have an external 9v battery for motor and servo. Please help me connect the battery correctly or change my code?  Speed = temp * 6.375 why? because= max speed is 255, and i think 40 *C is a max temperature + 10*C was the lowest temperature and 64 was lowest speed i preferred. so 255%40 = 6.375 to test then i used lowest temp and speed. 64%10 = 6.4 so i thought 6.375 was good because any higher would mean it would reach a number higher than 255. but this equation seems to give decimals, maybe arduino wont read decimals as speed? or am i coding for something different than what i want to accomplish?  english is my second language there fore it was probably a bit unclear to understand, sorry! Copy of Code: //Temperature Run fan with Servo angle tilter #include // Servo library of commands #include //lcd library of commands LiquidCrystal lcd(12,11,5,4,3,2); //set pins const int temperaturePin = 0; const int motorPin = 9; Servo servo1; int speed; void setup() {     servo1.attach(6);   lcd.begin(16, 2);    lcd.clear();   lcd.print("Temperature");     pinMode(motorPin,OUTPUT);     Serial.begin(9600); } void loop() {   float voltage,degreesc, degreesF;   int position;     lcd.setCursor(0,1);   voltage = getVoltage (temperaturePin);   degreesc = (voltage - 0.5) * 100.0;     // Tell servo to go to 180 degrees, stepping by two degrees   for(position = 0; position < 180; position += 2)   {     servo1.write(position);  // Move to next position     delay(20);               // Short pause to allow it to move   }   speed = constrain(speed, 0, 255);           float (speed);      {         speed = degreesc * 6.375;         analogWrite(motorPin, speed);      }      lcd.print("  deg C: ");   lcd.print(degreesc);   Serial.print(degreesc);     } float getVoltage (int pin) {   return (analogRead(temperaturePin) * 0.004882814); }

Question by Fernando T   |  last reply

### Random distance driving question

This is a question that has bugged me since I was a child.A fuel tanker holds about 7,000 gallons.An articulated lorry has a fuel consumption (when fully loaded) of roughly 8mpg.That equals something like 56,000 miles (or more than two circumnavigations of the world around the equator) if the tanker used the tank as a fuel supply.The little boy within me wants to know has anyone ever done this? (I suspect they haven't actually driven an artic all the way around the equator, but you know what I mean)If not, does anyone know of similar distance-driving challenges?We're down to our last four feet six inches of black stuff, sir

Topic by PKM   |  last reply

What will be the equation for y for the following graph? y=5, x=0 y=4, x=1 y=3, x=2 y=2, x=3 y=1, x=4 y=0, x=5

Question by Wisaam   |  last reply

### Does anyone know where I can find a large(12" diameter) clear plastic, hollow sphere? Answered

It could be one piece or separate at the equator, or have a hole in it. Also, it doesn't have to be exactly that size.

Question by JamesRPatrick   |  last reply

### Reducing voltage in a circut for the layman.

I understand something, but for some reason I am unable to use that knowledge in application to find another answer. Let's say I am building something: (This setup is completely imagingary, so I will use strange numbers.) I have a battery box that has 4 AA batteries rated at 1.5V and 2.7amps (according to wikipedia).   Now lets say I want to hook that up to a LED that has a max 4 volt 20mA forward. I know that I need a resister. I know that V = IR. What I can't wrap my head around is this: How do I change that equation so that is tells me how many Ohms resistor do I need? Because according to that equation if I increase the resistance, I increase the voltage. Becuase were talking about the same source. Do I need to use two V=IR equations and solve for one then place that value in the original.   I just can't get it....maybe I have had too many beers since graduating, or using algeba? I need a layman's way of understanding this...(exasperated sigh...)?

Question by Asmodean_7   |  last reply

### 'sticks of butter'what are these? i.e. how much does a stick weigh?

I am wanting to make some cookies (American recipe) and it calls for 'two sticks of butter' - I need to know what this equates to in grams (or ounces I guess for Americans). cheers Lesley from NZ

Question by yapper   |  last reply

### "flute" hole size and spacing

I've got a clarinet mouthpiece and some pvc pipe...25mm but i'm sure I can adapt it bigger if necessary. Is there some elegant equation (like where the natural harmonics on a guitar lie) to calculate the spacing and diameter of the finger holes for chromatic tuning?

Question by timgray   |  last reply

### Nuclear power costing

I am doing the cost of electricity for a nuclear power plant and was wonder if this costing equation seems right:  Take a plant at the cost of $7 billion and produces 1100 MW of power 7000000000/1100/1000=$ 6363.63 per kW Normally the life cycle is 40 years and a weighted average cost of capital is 14.50% So 6363.63 kWh * .1450 = 922.72 The typical capacity factor ranges from 75% to 85% so the average will be taken 80% This capacity factor is then multiplied by the number of hours in a year which is 8760 0.80 * 8760= 7008 kWh a year the plant is running So: 922.72/ 7008 = 0.132 which is 13.2 cents per kWh. Operation and maintenance costs with fuel is estimated at 1.5 cent per kWh Property taxes is at around $0.02 cent/kWh Fuel cycle is at around$0.03 cent/ kWh Waste cost and the decommissioning costs together are 0.02 cents/ kWh So the total cost stands at around 21.7 or 22 cents per kWh ive done another equation out for 3rd generation reactors that comes out at a lower cost. does this seem right? i am not sure how to work out the weighted average capital cost % (that was a figure i took from a site) i will be grateful for any reply

Topic by rich5007   |  last reply

### Calculating the ripple current of the output filter of a full bridge smps?

I have been designing an offline 100khz 720 watt full bridge converter for 24 volts dc out at 30 amps. I've calculated that at a minimum duty cycle of .3 and a voltage ripple of .03v I need a minimum of 7k uf. I read the output filter section of "The Power Supply Cookbook" and it gives  this equation to get the peak to peak current ripple: I(pk-pk)=(2*Iout)/(min duty cycle). with a duty cycle of .3 this gives me 200A ripple current. With four caps each would need to be about 2000uf and a ripple current of 50A, which would be expensive. I've only every built flyback and boost converters so I wonder if the equation for peak to peak current ripple is only meant for those topologies, or perhaps I've calculated wrong. Is there a different equation I need to use or have I done something wrong? Any tips for selecting capacitors and what chemistry to use (tantulum/aluminum)? Thanks in advance I'm new to forward mode converters!

Question by sk8aseth   |  last reply

### You know how in the northern hemisphere toilets flush forward and in the southern they flush the oppposite way?

What would happen if you were in a plane and flew over the equator while flying. Would it like stop and turn around. My friend asked me this and now im curious

Question by octopuscabbage   |  last reply

### can you help with homework?

Im in algebra 1 and need help on a word problem The scenario is a cinama sells 532 buckets of popcorn for 1489.50. A large bucket sells for 2.25 and a jumbo sells for 3.75. Questios: 1.write an equation to model the situation (slope intercept or something) 2.how many jumbo buckets were sold?

Topic by fretmelter   |  last reply

### How can I calculate the RPM of a motor running at less than Maximum voltage? Answered

I'm working on a project that needs a certain RPM of motor. I am looking at motors from http://servocity.com/html/3-12v_gear_motors.html. I will be running these motors at ~5v. Is there an equation I can use to calculate this sort of thing?

Question by sblaptopman   |  last reply

### What is the strength of the other charge?

I need help with solving this problem in physics class. I know Coulombs equation F= k(q1q2)/r^2 The force between two charges is 2 newtons. The distance between the charges is 2 x 10 ^ -4 meters. If one of the charges is 3 x 10 ^ -6 C, What is the strength of the other charge?

Question by Baseball24_7   |  last reply

### TI Calculator Help

I have the TI-84 Plus Silver Edition and I have some questions. First I need to know how to graph the equation (x is greater than or equal to y) Also I put the quadratic program on my calculator but it gives the answer in decimal form, how do I view it in fraction form or is that even possible??

Topic by thouse   |  last reply

### How do you make your computer make money for you? Answered

I have a friend who said he makes 37 cents an hour or rather his computer makes 37 cents an hour for him making some sort of equations for people to solve and I was just wondering how I can do this.

Question by sf49ers   |  last reply

### How can I make a bicycle generator?

Im doind a science fair project and I'm having quite a bit of trouble. For the fair I am trying to connect a generator to a stationary bicycle and then to a television. How should I start. I don't even know where to begin. Any thoughts, ideas, equations i may find helpful. whould be great.

Topic by rlouise   |  last reply

### just cos its winter in america doesn't mean it is everywhere else

Just because its hot in america you guys are making a big fuss on how to stay hot. down in melbourne australia it was 40c+ (104f+) for three days straight then the next week is full of 30c+ (86f +). instructables is viewed worldwide in both sides of the equator.

Topic by 11orem   |  last reply

### how to calculate heat transfer rate through a heat pipe ?

Objective: maintain a temperature of water feed into an equipment to be ( 0C-20C). he surrounding temp is about -15 C in Winter and 40 C in summer. I would consider the soil as a heat sync. Any equation to calculate the amount of heat the heat pipe can transfer or  be dissipated  ? Thanks !!

Question by sultan86   |  last reply

### Why do people believe that a cat bringing a headless mouse into the house is a gift to the owner ? Answered

It just doesn't make sense to me; in my experience the cat brings in a mouse , plays with it until it's dead and loses interest; the owner seems irrelevant to the equation. I like cats but they do not strike me as being particularly altruistic, Any ideas?

Question by FriendOfHumanity   |  last reply

I need some help in this homework. Foil length of strain gauge is L Resistance of strain gauge is R Equation is deltaR/R=0.485(deltaL/L) the strain gauge is given a strain of X%. The question says to calculate the change in resistance on the strain gauge. My problem is that i don't understand the X% strain. I'm not asking for answer, just want to know what the X% strain means

Question by ARJOON   |  last reply

### resonance wireless inductive coupling final year project (wireless handphone charger)

Hi im doing wireless inductive coupling using square coils.Anyone can advise which equation to determine the inductance? i dont have a LCR meter :( I have problems combining my full wave bridge rectifier and voltage regulator. Do i need impedance matching?

### Can the pressure of an input water source in a laminar flow setup be variable? Answered

I.e. Can I change the total ballistic traveling distance of the water stream by lowering/raising the water pressure into the laminar flow nozzle assembly? I can't seem to find any theory/equations regarding laminar water flow and how pressure fits into its creation. Thanks for any help everyone!

Question by kidiron   |  last reply

### Nova's Elegant Universe

Nova's Elegant Universe is a very well made scientific documentary about string theory. If any of you have been interested in The Fabric of the Cosmos by Brian Greene but don't have a chance to sit down and read something. This is for you.String theory is trying to unify our understanding of everything through one equation, if you think that is interesting then: Click here to watch the entire series // More Brian Green at TED here \\

Topic by lamedust   |  last reply