Danijel Gorupec

I suppose that you 'must' keep surorounding pressure equal from all directions (otherwise it would be possible to produce dinamic pressure differences - sound waves - that would break the eggshell apart).

If I am correct, the eggshell permits air, so you will have your chance only if you change the air pressure really rapidly. Still, it would not be easy at all.

Maybe, it would be easier to rapidly decrease pressure than to increase - the eggshell should be easier to break from inside. So, maybe the easiest recipe would be to slowly increase pressure and then rapidly decrease it.

I cannot give you any numeric value, sorry.

Another idea... if temperature can be increased (by pressure increase), you may boil the egg. Boiled eggs break sometime. If you do it rapidly enough, steam from the inside might explode the egg.

I once wrote a small article about torque vs power and their influence to vehicle acceleration. I re-edited it now and posted down (I planed to put it on my web site for long time but never finished it, so thanks). Maybe you will find it useful. Sorry, it is somewhat long. Also note that it only explain basic stuff. If you need more details (engineer-level knowledge), then, yes, you should turn to books.

...

The thing that moves your motorbike around is the force that tire exerts on pavement. I will call this force ‘the thrust force’. If the thrust force is greater than drag forces (mostly wind resistance) then your motorbike accelerates. If the thrust force is exactly equal to the drag, then your motorbike keeps running at constant speed.

There is a very simple formula that tells how much your motorbike will accelerate if we know the net force acting on it: a=(Ft-Fd)/m (where ‘a’ is the acceleration, ‘Ft’ is thrust force, ‘Fd’ is drag force and ‘m’ is the mass of the motorbike, driver and cargo). To make your motorbike accelerate faster you must either decrease its mass or increase thrust force (or you can even decrease drag force, but effect will be small on low speeds).

So, how large is the thrust force? It changes depending on how much throttle you give and what gear you use…. please, read further.

At any moment, the amount of the thrust force depends on the amount of torque exerted on the driving (rear) wheel of your motorbike. Larger the torque, larger the force. There is a simple formula: Ft=Mw/r (where ‘Ft’ is thrust force, ‘Mw’ is torque on the wheel and ‘r’ is wheel radius). You can see that the thrust force also depends on wheel radius – smaller the wheel radius, larger the force, greater the acceleration (theoretically). But you can rarely change the radius of motorbike wheels.

One important side-note: The thrust force is also very limited by friction between tire and pavement, and cannot pass over this limit. That is why often the best way to achieve better acceleration is by installing stickier tires.

The torque is a bit foggy term for those that never liked physics. In the world of wheels and axles, the torque is a value that is analogue to the force of the linear world. The torque tells with how much ‘strength’ something is twisted (while the force tells with how much ‘strength’ something is pushed/pulled). With the already mentioned (M=F*r) formula you can convert torque to force and vice versa… force can cause torque (like when you use a wrench), and torque can cause force.

So how large is the torque on your motorbike driving wheel? Well it depends on two things: on the torque generated at engine shaft, and on the gearbox ratio. The formula is simple: Mw=Me*N (where ‘Mw’ is torque on the wheel, ‘Me’ is the torque on the engine shaft, and ‘N’ is gearbox ratio – like 1:N).

As you can see, the gearbox ratio is very important. This is not surprising because the function of the gearbox is to adjust the torque level at your driving wheel. Larger the gear ratio, more torque on the wheel, more thrust force and therefore greater the acceleration…. again, in theory only. It is important to note that there is no sense to put 1:1000 gear into your motorbike – you may achieve great acceleration with this, but only for very short time because you will hit on maximum engine revs while still driving very slowly… and you would have to have some impossibly sticky tires.

Still, for greater acceleration, one must keep gears low as long as possible (late shifting).

And how much torque is there on engine shaft? Well this depends on your engine capabilities and how much throttle you give. Engine capabilities are described with torque curve. Torque curve tells what is the maximum torque (that is, ‘on full throttle’) the engine can produce at any given engine revs.

Still, absolute value of your engine torque is not that important for your motorbike acceleration. Even if your engine can generate only a small torque, you can easily enlarge it by using higher gear ratio in your gear box. Yes yes, we said that high gear ratio reduces maximum speed of your motorbike – but what if your low-torque engine is the one that can run into very high revs? This way, even with high gear ratio you could still obtain some respectable speed, and have acceptable acceleration at the same time.

Strange, isn’t it? You can have high-torque-low-revs engine or you can have low-torque-high-revs engine, and both can achieve similar results. You only need lower gear ratio to the first one and higher gear ratio for the second one... It really is that way.

Okay, if torque doesn’t matter, what matters then? What matters is product of the torque and revs. You must multiply the torque that is your engine capable with max revs that your engine can achieve – the product will be a good estimation of acceleration capacity of your engine… Do engine manufacturers already give this number in their engine specification datasheets? Yes, of course, this is the first number you see – the power!

The power is the product of torque and rotation speed.

Because gearbox ratios are always near-optimal in real-world motrobikes, you can quickly estimate their acceleration abilities only by looking at the engine power and motorbike overall weight (mass).

For more precise acceleration estimation, you must consult either power curve or torque curve. Their shapes are important. For example some engines will not want to accelerate your bike at low revs, but will go mad at high revs, while other engines may provide more constant acceleration over full range.

Obviously, from the torque curve we can produce the power curve of an engine and vice versa. Reasonably, the power curve will have its maximum at higher revs than the torque curve. But either of these two curves is enough to predict the acceleration behavior of your bike (sure, you must also know: gear ratios, rear wheel diameter, tire/pavement friction coefficient, aerodynamic drag and rolling resistance, mass of vehicle+driver+petrol+anything). This should be enough for ‘a regular person’.

As for gearboxes, it is better if they have greater number of ratios because with large number of gear ratios you can hold your engine at narrow rev band. Of course that you will choose the band that is around peek-torque on the torque curve… Actually, if you had continuous-variable-transmission, you could keep your engine always exactly at the peek-torque gaining maximal acceleration. There are however technological reasons why normal motorbikes don’t use transmissions with 30 gear ratios nor CVTs.

One can fairly safely assume that the gearbox will be optimized for speeds between 60 and 110km/h with those power figures -- unless the bike is very old. Five-six speed gearboxes are normal and even four speeds is enough to get a decent range of ratios.

Even cruisers and scooters behave fairly similarly at slow speeds (up to 100km/h) with modern suspension on good roads, learning to control them is a bit different, but the performance is much the same.

Yes, I agree... But from question I assumed that The Ultimate M needs explanation of more basic stuff (power, torque...). That's why I want to be sure he/she understands the gearbox is important. If The Ultimate M already knows this stuff, then I apologize for underestimating his/her knowledge.

You told us a lot about your engine, but you said nothing about your gearbox (gear ratio and gearbox type) and diameter of your wheels. If you understood above answers, then you also understand now that gear-ratio and wheel-diameter is as important to your bike (how it behaves in driving) as engine specifications.

Do you have any kind of gear-ratio-adjustable gearbox on your bike at all?

I also agree... Only, I beleive, there is no guarantee that their voyage will end in democracy. I actually beleive that democracy is only born by chance - no guarantees at all... In my country we all hoped to make a democratic society, but we didn't make it (we still have no idea what went wrong).

(For fun, I like to make a parallel between democracy and intelligent life... There is no mechanism in evolution that will inevitably (or even likely) produce human-like inteligence. Human-like inteligence is created by pure chance - by series of non-connected mutations. However, once created it is able to sustain itself for some time. )

A car that could use a flywheel -> maybe a dragster racing car (was there any effort on making one, if anybody knows?).

The gyroscopic forces are going to be significant. What's going to happen when you try to drive on an inclined/crowned/etc. road?

Yes, this seems like a problem... On the other hand, a military fighter aircraft seems quite agile despite the fact that jet engines spin very fast. I have no idea how jet engines are not torn apart when an aircraft changes pitch.

I mostly agree with you... a "hero" is a personal trait. You cannot realy be a hero by profession.

However, we pay them to be heros - to risk ther lives in order to save our lives or goods. So, we like to think about them as heros - we feel safer and money we spend seems justified.

There is also a less romantic view - by calling them heros we can also pay them somewhat less. They will do their job for pride (and will be more efficient when duty calls by not having second thoughts - people tend to play their roles).

Still, there are real heroes among them.

(EDIT:obviously, I would consider myself a hero after I learn my English. Sorry.)

Flywheels, I feel, are somewhat udervalued - I hope that there will be more flywheel talk-about (also on this forum). But the flywheel is not ideal car-energy-source. The flywheel is ideal when you need lots of mechanical power (energy release in short time).... Also, I beleive, in space missions, flywheels could be easier to deploy (zero gravity, vacuum) - could be used to convert small-power energy source (like PV cells) to on-peek-demand high-power source.

CaptainPanic - be merciful to non-gasoline energy sources. Don't 'kill' them by comparing them to gasoline... Gasoline is certainly unbeatable by all counts - anything compared to gasoline seems plain useless. Gasoline looks like "out of this world". We were blessed.

(And yes, I would certainly count compressed air as a mechanical energy source.)

Hi,

1. Yes, it is correct.

2. Your math is right.

Notes:

- in some cases adding a 10 ohm resistor to the circuit might change current significantly. However, this is probably not the case in your case - I guess this because current is very small so I suppose that overal resistance of the circuit is much larger than 10 ohm.

- You don't need 7 watt resistor for such small current

- If there is already any other resistor (of known value) in the circuit that caries all the current, you could simply measure voltage over it (this way you will be sure that you didn't disturb the circuit by adding 10 ohm resistor to it)

- Most important: Because voltage measured is very very smal, I doubt that your measurement is very precise (unles you have a very very good instrument and you care about many things). Try with 1000ohm resistor - it should develop cca 0.5V. If it develops significantly less, then obvously 1000ohm resistor disturbs the circuit too much.

Green Xenon, what problem are you trying to address with such device? Why is it important to use purely-natural gas? Why it must be filled with helium prior to ignition?

(BTW, transporting "purely-natural" gas through pipes seems harder than transporting methane-ethane-only mix. Propane and Butan are prone to liquification under pressure or low temperature and it is difficult to transport something that is part liquid, part gas. Clean combustion of such wide mix also seems problematic to me.)

Why not just slowly lift something up into space...

I am sure you will be fascinated with space elevators (just google for "space elevator", there are nice images) - I was, and still I am.... NASA also knows about it.

In the vacuum tube elctrons move at relatively high speeds. However in the wire, it is much different - the wire is already completely populated with electrons. If you put one extra electron inside, others will fill the jam and will quickly readjust their positions. Electrons won't actually move much, just a few nanometers to reach new equilibrium. But the disturbance will quickly spread along the wire (like a wave).

Electrons 'feel' other electrons because of the negative charge they posses. That's why they don't like 'standing' too close to each other.

When a signal is transferred from point A to point B in a telecommunication wire, it is not that electrons are moved from point A to point B, but instead a disturbance is generated at point A, then the disturbance spreads along the wire and is finally detected at the point B.

The above is very simplified. Other people may provide 'harder details'.

The analogy with water pipe is okay enough.

In water pipe: one molecule is forced into pipe, the disturbance spreads rapidly along the pipe (at speed of sound in the water), and another molecule drops out on the other end.

In wire: one electron pops in, the disturbance spreads rapidly along the wire (at speed close to the speed of light), and at the other end an electron pops out.

The important thing is that electrons move very slowly, but disturbances move fast.

But why do you say that this is not 'well known'? Do you mean 'in general population'?

Also, I think, you may first check your computer for viruses and other unfriendly software.

I quickly read the article and liked the idea to use cheap HVAC equaipment to generate el. power from moderate temperature geothermal source. The HVAC equipment is mass-produced and is therefore much cheaper than specificaly designed power generation equipment. This can make even moderate temperature geothermal sources useful for power generation despite the very low efficiency that is achieved (Ranking cycle: small temperature difference -> low efficiency).

However, HVAC used that way has nothing to do with 400% 'efficiency' that is achieved when it is used for heating. It makes sense to use HVAC systems for power generation because of their low cost, not because high efficiency.

Now, it's not all bad.

You still have 220 other units of heat, that you can use to heat the house. The principle is called Combined heat and power.

I beleive that here you made a mistake (in otherwise excellent post). You don't have these 220 units of heat any more. You had to release them (into the cold reservoir) in order to create 80 units of electrical energy. Therefore you lost 20, and that's it.

If you wanted to use the 'combined heat and power' you could make, say, 20 untis of electicity (for this you may spend 75 units of heat), and use the rest (225) for heating... In any case, it is better to spend electricity directly instead of first powering heat-pump and then use another heat-engine to generate electricity back.

Okay, ponderer, I see you think hard about it.... however, I will stick to my first answer.

In first part of your mail you are describing a heat-pump. Heat-pumps can really achieve 400% 'efficiency', but the word 'efficiency' is here used in more loose way than ussual. As CaptainPanic said, using the word efficiency in that way, you could easily say that an oil well has 100000% efficiency.

The 'efficiency' of a heat-pump strongly depends on the temperature difference between the cold reservoir (underground temperature) and the hot reservoir (your home temperature). Larger the temperature difference, smaller the efficiency. This is by the law of physics, not only by the construction issues.

In fact, if the temperature difference is infinitesimally small, you can theoretically achieve infinte 'efficiency'.

(Imagine this.... if there would be no 'efficiency' dependence on the temperature difference, then we could easily build a heat-pump that can boost the temperature for 1000000K with 400% 'efficiency'. Not possible, unfortunately)

With a heat pump, and with reasonably small temperature difference between hot and cold reservoir, you can spend 100 energy units of electrical energy (for compressor) to extract 400 energy units of heat. The energy is not created, but is extracted from the cold reservoir. As a result, the cold reservoir becomes a bit colder, and the hot reservoir a bit hotter (the temperature difference increases). Fortunately, the cold reservoir is large enough (the underground) and this works infinitely.

....

To generate electricity you also need a hot and a cold reservoir. You must transfer the energy from hot to cold, and extract some mechanical work in the process (used to drive a generator). This is actually the oposite of the heat-pump process.... (here you can read how it is done in a thermal power plant).

Again the laws of physics don't allow that we extract all of the energy that is transferred from the hot to the cold reservoir. Only a percentage of it is theoretically possible. In fact, the process is more efficient if there is large temperature difference between hot and cold reservoir.

In fact, if the temperature difference between hot and cold reservoir is infinitesimally small, you can only achieve zero efficiency - you cannot make any electricity. This is why you don't see large thermal power plants that extracts heat from the Gulf stream - altough there are enormous amount of heat available, the temperature difference is very samll and the power plant will be very inefficient (even with coolants that undergo phase-change at that temperature difference).

So, if you have underground temperature of 280K, you can probably heat your home to 300K using a 400% 'efficient' heat-pump. But you cannot then use this same temperature difference (300K to 280K) to generate electrcity with more than 25% efficiency. Therefore your 'efficiencies' will cancel out.

If, on the other hand, you use an heat-pump to boost underground temperature (280K) to 1000K, you will not be able to achieve 'efficiency' greater than, say, 120%. During the electrycity generation (1000K to 280K) you will be able to achieve maybe up to 80% efficiency, but this again cancels out.

...

You also talk about phase-change importance. Yes, the phase-change is very important and it boosts efficiency. But never above the theoretical maximum. Physics is a worthy opponent.

Please ask, if you think that I can explain my point better.

(*Sorry, I write in Kelvins because I don't understand Farenheits, and I am not sure if you/others are fluent in Celsius. Cultural differences.

Ponderer,

Can you clarify your question... Do you talk about hot underground water or about cold (you mentioned 'old spot') underground water?

Talking about "efficiency" is indeed misleading this case, I agree with CaptainPanic.

Do I understand you question correctly... you want to spend 100 units of electrical energy to get 400 units of heat, and then convert these 400 units of heat into more than 100 units of electrical energy? This, of course, cannot be done.... but you can still generate some electrical energy (<100 units).

You can achieve 400% with a heat-pump only if there is relatively small difference in temperature between hot and cold heat reservoir. Larger the temperature difference, smaller the efficiency you can achieve. The oposite is when you try to generate electricity... smaller the temperature difference, smaller the efficiency. Therefore, those two 'efficiencies' cancel out.

Here can read a bit more about heat-pump efficiency.

The answer to the first question depends on many things: motor construction/type, motor load... For example, number of revolutions of a brushed DC motor with permanent magnet is approx. proportional to the voltage supplied. On the other hand, the speed of an (non-loaded) asynchronous AC (cage) motor or a synchronous AC motor doesn't depent much on the voltage supplied, but on the frequency instead.

In the second two questoions you ask about energy... this is easy... The efficinecy of a modern dinamo/generator is quite high and therefore the produced electrical energy / power is just a bit less than the mechanical energy / power you put into.

(this post might suit better to the Engineering forum)

The ‘speed of current’ doesn’t have much meaning. (The strength of current does.) You would be surprised how slowly charges move in the wire.

A wire is all ‘stuffed’ with charges. If you somehow ‘push’ a charge at one end of the wire, the effect (like wave) is rapidly transported to the other end (at speeds comparable to the speed of light). Charges themselves are not moved much.

In AC you shake charges at one place of the wire. These charges push other charges near them and so on... the wave spreads fast. In AC, charges actually don’t travel – they only ‘shake in place’.... In DC, they do travel, but at incredible slow pace.

AC does produce a bit more loses in a wire (skin effect), but for low frequency (60Hz) theses loses are not that much.

AC might be better for power distribution because it makes things simpler (and possibly cheaper)

- AC is easily produced by power generators (no need to commutate high currents)

- AC voltage can be simple stepped up/down by means of transformers (transformer do not work with DC). By stepping voltage up, we can reduce power losses during transmission

- AC can be directly used by asynchronous motors.

(Today, we have systems that can efficiently convert AC to DC and vice versa, so sometimes you will see large power lines carry DC instead of AC. This is because transferring DC is a bit more efficient, as I already said.)

DC cannot be used in transformers. More complicated systems (DC/DC converters) are needed to transform DC voltage level.

A transformer is a simple magnetic machine. The primary winding produces magnetic flux. This magnetic flux goes through the secondary winding. The fact is that a voltage/current will only be created in the secondary winding if the magnetic flux changes with time (Faraday’s law). Therefore, the current through the primary winding must be AC – this creates ever changeable magnetic flux, that creates voltage in the secondary winding.

Sorry, long post.

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?