Danijel Gorupec

You started right! Notice: a) the voltage drop on the 4ohm ressistor is the same as voltage drop on the 12ohm resistor (these two are in parallel) B) voltage drop on the 4ohm ressistor (or 12ohm resistor) plus voltage drop on the 7ohm resistor equals to 20V c) current through 4 ohm resistor + current through 12 ohm resistor equals to 2A d) power dissipation can be calculated: P=voltage * current The Ohm's law you already know

I was also upset about this thing for some time. And yes, I believe that this is totally possible and is actually happening. (I live in a village, and if the whole village somehow gets transmitted 200 years ago, we would have no idea how to live – how to make a soap?) But then again, people do reinvent things all the time. (I work in a company where we always reinvent things because we ‘forget’ how we did it last time . I stopped worrying about the technology loss when I realized how often this actually happens. I always considered fall of the Roman Empire as a notable example of the technology loss. (I only disagree with you when you call ‘CPU etchers’ a vital thing.

I think, it would be much easier to expand average human lifetime to a thousand years (probably by slowing us down - like extremely slow turtles). This way stars would at least seem closer.

I agree with D H. In many sports there would be no female competitors at the highest level, so we have separate (female-only) competition. I wanted to ask an additional question - is the 'men competition' actually 'man-only competition' or is it actually the 'ultimate competition'? For example, if a woman can run 100m in 9.80, will they allow her to run side-by-side with mr. Bolt, or there is no such possibility. Anyone knows?

Thanks Swansont. I am aware of resistive heating. Still I was thinking if there is any temperature effect from 'stuffing more electrons inside' - as it would be when you stuff more gas into a container (adiabatic heating).

Hi, If you have a simple capacitor made of two identical metal plates. After you put a charge on it... 1. does the negative plate becomes any heavier (greater mass) than the positive one? (For the difference in number of electrons inside. Or am I missing some other effects.) 2. does the negative plate becomes any warmer (higher temperature) than the positive one? (Because I imagine electrons as a 'gas' inside metal -> 'pressure' is reduced on the positive plate, and increased on the negative.) Thanks.

Impressed with your method! (Of course, the programmer of such algorithm will have to find a way to reject phone numbers and other digit-trains). But this could be the doable method to estimate the order of magnitude of the smallest never used natural number. I have no answer. The question is open. I am happy to hear your personal estimates (for order of magnitude). And I am even happier to hear about methods that can be used to 'calculate' its order of magnitude. Thanks.

1/8 inch still seems quite a lot (sorry). Do your best to reduce... You absolutely must have iron wherever the magnetic flux goes. Only small gaps are tolerable. (The iron is a highway for magnetic flux). You are happy becuase you can now optimize your alternator - you will learn a lot. First, I believe, you need to understand the exact magnetic flux path in your alternator so you can make it stronger.

Sure, it seems certain that you have high-voltage, small amps. The high-voltage transformer creates the high voltage (but transformers do not generate power). You may try without it (I would). If you have a voltmeter, you can check your output voltage without anything connected. And then you can check how much the voltage drops when you connect the light bulb. You will see that voltage drops a lot. Note that if you use lots of thin-wire turns in your generator - you will generate high voltage, but small amps. On the other hand, if you use smaller number of thick-wire turns, you will generate low voltage, higher amps. The power is proportional to amp-voltage product. It is hard to say, but I beleive that you should work on stronger magnetic flux in your alternator - do you use strong magnets, do you use lots of iron on your magnetic path, do you have small enought space gaps between iron/magnet parts?

Well, I beleive peopole did count up to one million - even on loud. Probably there were freaks that counted up to ten million (at least in their heads). But above ten million, there might be unused numbers. ... I beleive that peopole don't think about telephone numbers as integers. Instead they think about telephone numbers as array of digits. This is a different thing. Thanks for your replies

Stupid, but still interests me I define that a number is 'used' if at least once in history at least one human being ever used it in any way (write, read, tell or even think of), the question is 'what is the order of magnitude of the smallest never-used natural number'? Note1: numbers that are never used as numbers, but instead as array of digits, are not spent and are considered unused. For example, telephone numbers. Note2: numbers used inside machines (computers) during computation procedures are not spent (except if a human being reviewed the process and noticed them). Note3: just a brief look at a paper sheet full of numbers will not spend them all. To spend any you must actuall 'load it into your mind' as a number. I know that there is no definite answer. I am just asking what is your best guess. My best guess is that the smallest unused natural is in 100-million range. Or can it be even smaller?

Okay, thanks cypress for confirming my thoughts.

You can plan to do any job in phases. Somebody can ask you ‘in what phase of your job you are now’ and you will tell him ‘I am just finishing the first phase’. Similarly, an oscillator does a ‘planned job’ – it oscillates. You can ask ‘in what phase is it now?’, and the answer could be ‘it almost reached the upper point’. So, the phase tells us about where on its ever-repeating path the oscillator exactly is. As oscillators exhibits ‘circular’ behavior patterns (they just oscillate round and round) we like to describe its phase in radians (or degrees of arc). Zero radians means that it is just at the beginning of its cycle, pi radians means that is in the middle, and 2*pi radians means that it just closed its cycle (and is beginning the new one). Of course, this is possible only if the starting point is assumed. Two similar oscillators can have same frequency, but can differ in phase. One of them can be just ahead of the other one, for example. We say that there exist a phase difference between them. The phase difference is also mostly stated in radians, of course. The problem is that people sometime use word ‘phase’ when they actually mean ‘phase difference’. You may hear sentences like ‘first oscillator has phase of zero, while second one has phase of pi/4’. It actually means that there is pi/4 phase difference between them.... In equations you will find phi and this phi is about phase difference (in respect to some reference). Waves are a bit more complicated than oscillations because have spatial dimension. You may imagine a wave as an array of dots that all oscillate in orchestrated manner. Neighborhood dots are oscillating with just a slight phase difference. In one moment one dot is in some phase, just a bit latter the neighborhood dot reaches the same phase, just another bit later the next dot reaches the same phase and so on... The ‘phase velocity’ tells you how fast is this progressing through space. The phase velocity sounds fancy, but it is not (people use it every time when they talk about ‘how fast are waves on the sea’). It tells about propagation velocity of energy/disturbance in a wave.

A quick quesiton... Suppose there are two Ethernet subnets and a gateway in between. From one PC in the first subnet we are going to establish TCP/IP connection to another PC on the second subnet. Obvously, the default gateway IP address must be defined in the first PC. But the question is, should the default gateway be defined also in the other PC (this one is only accepting the connection)? (If I understand IP networking correctly, there is no need for the accepting side to know its gateway. But I am not sure.) Thanks.

Are robot visits (like googlebot) counted in statistics? I am just wondering what 'number of views' exactly means. Thanks.

Some capacitors (electrolytic capacitors) must be polarized in normal work - this is purely because of technology used inside them to separate two 'plates'. In an electrolytic capacitor one plate is a fluid (electrolyte), the other plate is metal (aluminum, tantalum) and the insulator in between is the metal-oxide layer. If you reverse the polarity, for some reason (beyond my complete understanding - I should learn chemistry better) the insulator layer gets destroyed and the capacitor gets short-circuited.

The magnetic filed is not really steady. It fluctuates (it is influenced by alternating current of aramture winding). By laminating, you reduce losses (by eddy currents). In servo motors, it is even more important to reduce losses.

MDJH, I don't think you can use standard inequality signs ('<' and '>') to compare such 'infinte' kind of numbers. These signs are not to be used this way. However, as math is just a construction, you can define your own operators 'less than' and 'greater than' and you can choose to use '<' and '>' symbols for them. Then you can define that 'lim f(x) > lim g(x)' if (and only if) 'lim f(x)/g(x)' gives real number greater than 1... There are no internal problems with this definition, so math alowes it... However, it would be nice if you can also find a good use for this math.

Glad to help . You can cut out any part or shape from a parabolic reflector, and the focal point remains intact.

Hi, I never saw any problem with this. You just cut out an 'asymetric' part of parabola shape (like the red part in the picture below).

Thanks ajb. I believe that I can understand your answer. Basically, you said that I should treat ‘value-unit’ pairs in my software as a class of ‘numbers’ and work with them. As a consequence, the expression ’20 m / 5 s’ has two members ’20 m’ and ‘5 s’ and the result of this division-like operation is ’20/5 m/s’. It would be difficult to implement this in the software so I will probably do it by applying some tricks (like hidden grouping). But I understand your point – I have no right to force the user to enter above expression as ’20 m / (5 s)’.

Hi all, (I wasn’t sure should I post this to Physic or Math forum. I decided to go for math.) Can anyone help me understand ‘connection’ between value and a physical unit. Somehow I always assumed that there is ‘invisible times’ operator between them (anticipated multiplication). For example when I write ’20 kg’, a always assumed it actually means ‘twenty times a kilogram’. But now I am not so sure anymore – for example, you cannot write ‘kg 20’. It doesn’t mean the same (or does it?). In some cases, it is beneficial to think about units as factors. For example one can write the following expression: ‘20 W * 3 s’ (twenty watts times three seconds) and this is equal to ’60 Ws’. However, it would be unusual (or incorrect?) to write the result like ‘W 60 s’. On the other hand, the following expression is what really bothers me: ’20 m / 5 s’ (twenty meters per five seconds). The result is ‘4 m/s’. If units are understood as mere factors, then the result would be ‘4 m s’ (taking in account that multiplication and division have the same order of precedence). What is correct then... Is there a stronger connection between value and a physical unit (stronger than multiplication) or should I actually write the above expression as: ’20 m / (5 s)’? Thanks (I was developing a piece of math software when I realized that I don’t understand this issue).