CPL.Luke

http://en.wikipedia.org/wiki/Bohr_Einstein_debate#The_principle_of_indeterminacy_applied_to_time_and_energy during the einstein bohr debates einstein proposed a very precise way of determining the amount of energy radiated in some very precise interval (detailed in the above link). originally stumped bohr later found a solution that showed that the error in the experiment corresponded exactly to the indeterminacy relation between time and energy. my question is if anyone here knows how to solve it out mathmatically as it seems like this would be a very cool derivation. (or if someone can find it layed out somewhere)

alright, I played with that a bit and I see that your right, it's still a bit odd though, espescially considering that the final momentum of the rocket is going to be equal to the mass of the propellant times the velocity at which its ejected, so in order to get the most momentum out of the fuel you would want to have the rocket eject the fuel at the highest speed possible, but if you want to have the most kinetic energy in the rocket you would want to have the rocket eject the fuel at such a speed such that its velocity with respect to us would be zero. SO my question is then are the two equivelant? or is the extra energy lost as heat?

swansont, Why would the transfer of energy from the propellant to the rocket be effected by the speed of the rocket? assuming the rocket ejects mass with a constant velocity, then the efficiency of the rocket should be constant, right?

is it just me or is the wavicle model all the interpretation that one needs? personnally I'm content with knowing that the wavicle expands as a wave between obserations and then collapses afterwords at the next observation. Also if the wavicle didn't collapse charge conservation would be violated, so that would explain why the wavicle collapses.

Rocket man you are right about the sum of the final momentum being the sum of the momentums of each particle fired, however you haven't considered the rate at which the particles are fired with respect to time relative to when the first reference frame, this is controlled by the amount of power the rocket has available to it. also I found this post on a cornell forum

the difference is in the mathmatics, The real definition of force is change in momentum with respect to time or dp/dt, now in a conventional rocket the mass changes significantly with respect to time, so the rate of change in momentum (force) becomes F=(dM/dt)V+M(dV/dt) not F=MA as far as I know the propellant mass in an ion rocket does not constitute a significant portion of the mass of the rocket and so F=MA works quite well, however if we wish to have a far more useful version of force for calculating the momentum of the rocket we should go back to dp/dt follow that through and you'll get F=dm/dt V where V is the velocity of the exhaust, and dm/dt is the rate of fuel consumption (in kg/time), integrating this with respect to time and we see that the final momentum of the rocket is going to be equal to m (the mass of the propellant) x V (the velocity of the propellant) in other words momentum=mv however like I said before the rocket is limited by power so the force is not constant and the rate of fuel consumption is changed in order to have the maximum possible exhaust velocity. ^that is how you would do the problem out using momentum, and it is useful as it allows you to find what the rate of fuel consumption should be. The problem with your reference frames is that you are in effect trying to define a force acting on the reference frame, and this invalidates it. It should be noted that the reason why saying a force is acting on a reference frame invalidates it is because you get non-sensical answers such as your saying the rocket experiences a constant acceleration under a constant amount of power, THIS DEFIES THE LAW OF CONSERVATION OF ENERGY.

a conventional rocket is different as the mass of the fuel is a significant percentage of the rockets total mass, and so the rockets mass varies in time and this changes the math quite a bit. So for the sake of simplicity we should only talk about ion rockets. [quote a rocket's power is measured in newtons not watts] thats like saying an electron's diameter is 5 ampere. Power has units of energy over time ie it can't be measured in newtons (which is a measure of force). furthermore your math doesn't work because the reference frames before (A) and after (B) have experienced some change in momentum or impulse from the ejection of the particle, your model can't define any acceleration of the ship as that would invalidate the reference frames.

Rocket man you misunderstood my terms, P represents power (FV or E/T), and you can be quite assured that power times time equals energy. You can also be quite assured that the basic laws of physics are the same on earth as they are in space, in other words my math applies to both the car and the ion rocket (conventional rockets are more complicated). the problem with your logic is that the limiting factor here is the amount of power available to the rocket and not the force applied, also be sure you don't think of the rocket's reference frame as a valid one, as it is accelerating.

who says an ion engine uses a constant force? if the engine is limited by some power supply then the speed that the craft can reach is somewhat limited by that fact, as the velocity v time graph becomes a square root function, and so after a period of time the acceleration on the rocket becomes neglegible. It was always my understanding that nasa doesn't use ion thrusters for speed, but instead for missions that require alot of delta v, Cassini used an ion engine because it needed to change course a number of times while it visited Jupiter's moons. note: here is the math to find the acceleration and velocity that any craft will have if it uses a constant amount of power to propel itself. PT=1/2MV^2 2PT=MV^2 2PT/M=V^2 (2PT/M)^(1/2)=V to get the acceleration just take the derivative of velocity (V) with respect to time (T), but so you can see that an ion engine will never get a craft up to a very high velocity without bringing with it a power source able to supply several kilowatts of power, also you then have to consider the power to weight ratio as the weight could have the same effect on the crafts performance as the lack of power.

has anyone ever factored in dwindling oil supplies into the models for warming? I imagine that any model out there is partly based on an increased consumption of fossil fuels over the next ten to twenty years, however if the supply of said fossil fuels dwindles naturally over the next ten to twenty years and thus effects the rate at which they are consumed, then global warming may not be as severe as previously thought so the question beomes "is there enough oil in the world to significantly effect the climate?" I know that this isn't taking into account coal and liquid natural gas, but I have a fealing that in the US at least as the oil runs out nuclear plants will be built to replace the oil ones.

yeah arther C clark explored the idea in his book 3001, the main character lives in a "space tower", its a tower that extends all the way up into space. Now the character lived in the part of the tower that was 1/3rd g year round, and because of this he couldn't go back to the surface

is it possible that there is enough energy in our corner of the universe to keep most atoms above the ground state?

cold fusion isn't complete junk, it just never proved to be easilly reproducible, and thus most scientists lost interest in it. THe real problem with it is that there was never a basics on up approach taken to the research, and so the research was always focused on a single vague experiment.

were assuming a known B/R/size of the sides of the loop etc. we could even know the rotational inertia of the loop, but we can't take any measurements once the motor is turned on. The reason I'm interested in a problem like this is that it seems very difficult to solve but a solution must exist (otherwise how would the universe know what the torque/angular velocity should be)

but I don't know the angular acceleration or the current, in the problem we only get the voltage. although we could have the rotational inertia.

alright so if I apply a voltage to a loop of wire in a constant magnetic field, then it should feel both a torque and after some period of time it will have a (presumed) constant angular velocity. my question is what that final angular velocity is going to be and or, the function of time that gives us the angular velocity at that time. also, what would the torque on the motor be as a function of time? I've been working on this problem on and off for the past couple days after seeing a simple electric motor demonstration, I ended up with 4 equations that I thought I could use, namely an equation for the torque on the loop as a function of I,angular velocity, and t; an application of kirchoff's first law that contains the variables I,angular velocity, and t; and an equation for the power in the circuit containing the variables I,torque, and angular velocity; also an equation for the magnetic flux, and then its derivative. note: for simplicity the loop of wire is square with the dimensions X x Y V=IR+d(flux)/dt power=IV=(torque)(angular velocity)+R(I^2) flux=XYB cos((angularvelocity)(time)) torque=IXYB sin((angularvelocity)(time)) now the big problem is that when you plug the flux into the equation for V and then you plug V into the equation for power, then plug the equation for torque into the equation for power, you end up with both sides of the equation being the exact same thing. This then prohibits you or I from solving anything at this point. Yet the problem has to be solvable, as by merely plugging an electric motor into a battery you will get a torque, and an angular velocity.

does anyone have first hand accounts of what people outside the US think of the US, (general perception, its policies etc.)? ie, oppinions of yourself, freinds, or family, not what you hear on the news. I'm kind of curious because of a book I recently read and a general belief that the current foreign policy of the US may be alienating other nations. I hope this doesn't turn into a debate to soon, as I am really interested in the starting oppinion, and even in the unlikely event that anyone could be convinced that their oppinion is wrong then there are still millions of other persons who have the same oppinion as they do.

^very good, the book "without marx or jesus" I'm sure has something to do with jesus in a part that I haven't go to yet.

It's a book by jean francois revel circa 1972 about the state of socialism in the world, and how america is the only country that posses the cultural ability to transform into a socialist society properly. Beyond that however the book has a number of other generally insiteful observations about the current and future state of foreign policy, among other things. I was wondering if anybody has read this book, or any other political philosophy books written by persons outside of the USA. I ask because one of the most fascinating things in the book is the authors description of French attitudes towards America, I'm both curious to find out if his observations were accurate in general, or if there are any other books that more accurately cover europian oppinions of America Also on that note if anybody here has there own oppinion on America I would like to here it, not for the sake of a debate on the validity of the oppinion (although it will most likely occur anyway), I mostly started this thread to get a real unaltered foreign view of America, its policies, and anything else you can think of.

"Good luck, your talking to a person who has to use a computer to do exams because his writing is so bad no-one can read it even after 4 years of attempted hand-writing correction courses..." I here ya, my hand-writing is so bad that I can't even read it ^on a side note is it just me or does that sound vaguely like a your mama joke....

just got out of my physics C test, thought the mechanics was on the easy side and the E&M was ok, but better than the calculus test

what city do you work in? London? anyway all the trains on the metro-north rail are full , to the point where its hard to find a seat unless I'm coming home in the middle of the day or at midnight. keep in mind that the train runs on electricity, and a very large portion of The US's electrical supply comes from oil. also the $20 was based on one day I went to the city, and ended up criss-crossing the island about 5 times, if I was going in for a day it might have only been $10, I used the $20 figure as that was the only time I drove into the city (about two months ago) so I used it to be accurate. The main expense in driving to the city is parking, which can be about $10-$15 for a day, however a number of offices maintain their own garages. something more unique to the city itself that affects commuters is that The main part of the city located on Manhattan island which contains some of the highest landvalues on the planet, and while I can't find any direct reference it was once quoted to me as being $900,000 per acre, and that still seems a bit small to me, considering that the population density of manhattan is 66,000 people per square mile. also NYC has the most utilized and extensive public transportation systems in the country, the trains are not going to get any cheaper with greater use.

I did not mean to try and get sympathy for americans, but just to stopgap any european complaining that the US has it lucky personally I live in Southern CT about 50 miles from NYC A large number of people I know have parents who work in the city, and my sister lives there. There are a large number of people who hop on the train every morning to get in the city, but anyone who looks at I-95 in the morning will know that far more take their car into the city. Living this close to the city makes it possible to take an occasional trip into the city with my friends, the following is a breakdown of expenses for a trip into the city either driving in, or using public transportation public transportation: two way train ticket: $21.50 2 ride metrocard (for the subway or bus system in the city): $4.00 total: $23.50 assuming only one destination in the city driving in: $20 for gas (if I take the right bridges I don't have to pay any tolls) my personal method is to take the car in, find free parking, and take the subway for the rest of the day. apartments in NYC are very expensive, and there are additional problems inherent to any city (although as cities go NYC is pretty good) that make it undesirable for raising children, this makes it difficult to live inside of the city, not to mention that the cost of living in the city is such as to make it cheaper to buy a house out in the country.

Holy hell, I just payed $3.30/per gallon of gas on friday. I don't know about the rest of the country (US) but its risen almost $.70 over the last 3 weeks or so here in Connecticut, and at this rate it'll be $4 a gallon before we know it. Now for all the Europians out there remember that a large number of americans commute for more than an hour a day and tend to use up more gas than the average Europian.

hey yourdad did you take the AB or the BC? I personally found the BC to be ok (pretty much due to time restraints)