CPL.Luke

also i'm using the term borrowed to mean that the sum of object A and object B's momentum is zero. so as an asteroid plummets towards the earth it borrows momentum from the earth, and accelerates. Likewise the earth borrows momentum from the asteroid and accelerates towards it.

ah, I was just skimming for latex mistakes and saw that. I think were thinking of two entirely different problems here. and we need a common diagram. because right now I'm saying that the water drops out the bottom of the hopper do to gravitational acceleration (therefore no momentum was borrowed against the hopper) instead momentum is borrowed against the earth, and the momentum is returned when the water hits the ground. and like you said if the water turned into dark matter and didn't interact with anything but instead was only attracted to the earth, then the water still merely accelerates towards the earth and the earth towards it. no reason why the hopper should move. now, if the hopper has a hole punched in it from any direction other than straight down, then its a different story and the hopper will gain momentum and accelerate.

I see the latex in the previous posts but the latex error message is still up on post 27

I would love to have the front page back, I loved having all of the top threads readily available, now i have to spend extra time searching through the forums.

hmmm never heard of that one

well there is a small reason to be fearful about wifi networks. the frequency that a wireless G network runs on (2.4 ghz) is the same that a microwave oven uses. While the quantity of radiation is so small as to be considered insignificant, there haven't been any good long term studies on the matter. except for cell phones having been all over for the past 20 years and not causing any noticeable harm (cell phones also use 2.4 Ghz) that being said i'm not losing any sleep over the wireless G router sitting in my room.

hmm still doesn't work for me. but as for the hopper, lets isolate the system such that were only looking at the exhaust water and can ignore everything else. to do this lets consider a hopper filled with someamount of water, and someone pokes a hole in the bottom such that the water falls directly downward into a perfectly level channel. the water will hit the channel with some downward momentum, which will of course be absorbed by the channel and the ground in turn. the water now has zero momentum, but as more water is still coming down out of the hopper, the water has to go somewhere, so it goes out in both the right and left directions, gaining some amount of momentum in each direction but because the rate of flow and velocity in each direction is equal, momentum is conserved. you seem to be assuming that more water will flow in one direction than the other, I don't see why your doing that, perhaps were both looking at different diagrams ie. on yours the channel is inclined?

hmm klaynos what is this trick you speak of? I tried googling for it and couldn't find anything. And I don't think its in my textbook You guys seem to start everything alot earlier over in the UK, in the US we don't usually start calculus until our senior year of highschool (18 years old) if we even do it then. Out of curiosity when do you start your mathematics studies? and when do you do all of the trigonometry? I know that the in the US the standards have been falling through the floor ever since the "no child left behind" act was passed. It made it so that every student who goes through a school system must do so well on a standardized test, or the school could lose its accredidation (and this does include people with mental handicaps). This leads to school systems catering to the bottom fourth of their student body, and the States lowering the standards in order to reduce the strain on underfunded school systems.

you also have the problem of shia militias still under the belief that they can get the whole pie and have a shia Iraqi state...

like I said before though, the water will be flowing equally in both directions, thus conserving momentum. no need for the hopper to move.

but what if your ading to identical waves?

in the setup you first used in your last post did you mean an inclined channel at the bottom? or a level channel? if it was a level channel and water impacted it while moving directly down, than the fuid will flow with equal velocity in both directions, and no momentum will be gained in the hopper car. if the channel is inclined, than the water will flow in one direction, and depart some amount of momentum into the earth causeing the earths rotation to speed up by a very small amount. you seem to be over thinking this problem, it doesn't matter what the water does after its left the hopper, there's no way for that information to be returned to the hoppper for it to matter, so the hoppers velocity is only dependant on the velociy with respect to the hopper that the water left the hopper at. (downward velocity doesn't matter as that momentum is conserved against the earth. as for your second setup with the dual thrusters, like you said the effects of the internal fuel movements cancel out in the end. if your simulating the behavior of the rocket, then it matters, not if your just analyzing end behavior like the rocket equation does. as for your simulations, out of curiosity what are you doing that requires that precission?

well I'll give you that it ignores thrust vectoring, and thrust variation I don't think anyone in their right mind would want to use it in a gravitational field. but you have yet to show me how internal fluid movements matter in this instance. you have shown me that a rocket can temporarily gain some velocity without ejecting any mass, but I have shown you that that rocket will imediatly come to rest once the fuel shuts off.

something tells me that the Iraqi government isn't calling the shots on this one, washington doesn't want Iraq to fall apart on them and if it looks like its heading that way and Bush wants more troops there we'll send more troops. however I have a feeling were just going to call it quits.

out of curiosity why are we generalizing to i thrusters? but only in your latest setup do you get a net gain of momentum in the hopper, and as far as I can tell that is mainly because the thruster closer to the tank ignites before the other one does. I don't see how this shows how the rocket equation is invalid, unless your tryin to say that it doesn't take into account opposing forces (which its not supposed to)

with the amount of energy these waves could carry I wouldn't be surprised if they caused damage even when something wasn't resonating with them.

also in the presentation given at google's tech talks he says that he was funded by the navy for the past 11 years under their advanced power systems programs. They believed that the devices could be used to power large ships without the danger of nuclear disaster.

actually if you note there are three setups the second setup has the water hitting the side of the hopper, and then trickling down a whole in the bottom. this means that once the water flow stops all the "borrowed" momentum will be returned to the hopper, and the hopper will come to rest. then in a final setup you have added an additional ramp to the hole, thus directing the water out towards the "back" of the hopper and then there is nothing to "catch" the momentum again and bring the system to rest. in the final setup the energy comes from the gravitational potential energy in the water. In your first two setups your essentially trying to put a boat engine in a bathtub and make the bathtub move, outside of wiley cyote this doesn't work. now for your new setup where is this assymetric fuel flow that you speak of? you already said that the thrusters produce the same amount of thrust, and use the same amount of fuel to do so, if this is the case then there is no assymetric fuel flow to create your momentum. however if you mean that because of the difference in the length of pipe to the thrusters one of the thrusters will fire first compared to the other, then of course you will have a net gain in momentum by the hopper. also the rocket equation only involves the final velocity of the rocket for any amount of expended mass. So you because in your first two setups the final velocity was zero, you can see how the internal fuel movement doesn't matter. Also in your third setup (the one I call your third) the hopper did eject fuel and is thus able to gain a net velocity. actually your experiment does make for an interesting idea, a spaceship could potentially produce "impulse" without expending any mass as long as it had a very large amount of energy at its disposal

alright so hydrogen cars seem like a good idea until you think about how explosive hydrogen is, what happens when there's an accident? and if the car did explode in a place like NYC or in a traffic jam, what woud happen to the other cars in the area? could you have a giant chain reaction?

well for the first one look at what identities include cosx ^2

I'd personally be very nervous about running RF fields strong enough to power devices anywhere where i'm around. the risk of someone's pacemaker or hip replacement, or bone pin becoming a torch inside someone's body is to high. Also I wouldn't trust that a field that strong wouldn't mess with my neurons a little bit.

I got this prolem on a homework a while ago and I couldn't quite make sense of the book answer (and my professor can't really comment on it) say that you have two identical waves traveling along a string, what is the average power of the two waves. I said that it would be twice the power of one wave, because if you imagine two strings that are joined in a Y formation, and you send a wave down the two top ends of the Y, then the two waves join and travel down towards the bottom of the Y. because you put a certain amount of power (p) into each wave at the top you should get twice the power at the bottom (2p). but his was not the solution in the book, the book said that the amount of power of two identical waves traveling down the string is 4 times the power of just the one wave, because the formula for the power in a wave contains a maximum amplitude squared term. this means that because the amplitude is doubled when there are two waves the average power output must be 4 times that of one wave. I know that the latter interpretation should be correct, but I can't figure out how to reconcile that with my original interpretation.

oh woops, I knew i should have looked that one up properly before posting

actually that a legitamate line of research, IEC devices have been around for ages but nobody could get them to work. I always thought that it was the most promising line of research. And you can make tabletop versions of this with hardware parts, there was some student up at ohio state who was able to build one of them. also check this out http://en.wikipedia.org/wiki/Inertial_electrostatic_confinement I think the first one was made back in the thirties actually

who says that the center of mass of the system has to be stationary? if I have a train car and I drop a 5 ton wait on one end of it, the center of mass moved, but the train car most certainly did not. However the main thing in your problem is that there is a delay between the time that the liquid hits the top of your hopper car, and he time it hits he inside of the car and comes to rest. once the liquid has impacted the inside of the car and come to rest, the momentum cancels out, so shortly after you turn the water off the hopper will come to rest. same thing happens in your second model with the hole in the bottom of the hopper. because the hole leaves the liquid falling straight down, the total momentum still goes to zero after the fuel stopped moving. In your third model where the fuel is directed as it leaves the hopper, that one actually does have a net effect, as your effectively taking the gravitational potential energy that the fluid has and using it to move the hopper. but if you look carefully at your third setup the net force that the hopper feels over the course of its "burn" is due only to the water being directed out the bottom of the hopper. A similar thing will happen in the rocket, when you first start the pumps inside of the rocket you may get some odd motion, but all of the momentum that was carried by the fuel internally will total out to zero, and any temporary velocity changes will also go to zero by the time the rocket has finished its burn. also if you disagree with my interpretation of the hopper situation, can you please post a diagram of your setup.