A rocket becomes lighter as it gains speed. Therefore, if you would convert its final kinetic energy (lots of speed times much less mass) back to usable energy again, you would end up with less than what you spent to get it (and much of its fuel) up to speed.
The EM drive, though, keeps the same mass. That means that, assuming force and energy consumption remain the same at any velocity, at some point you indeed start to create more kinetic energy than you put in.
Sure, something else must be wrong. But that's not it.
You are quite right about tidal effects causing precession, and your links were very informative, but meanwhile I figured out that this is not what the actual paper was about.
Yes, Pluto and Charon are tidally locked because of the mechanisms you described. That happened very long ago.
However, more recently, the redistribution of mass on Pluto's surface caused the whole surface to realign itself with the axis of rotation (which did not change). So Pluto's axis did not tilt (at least not due to the described effect), it's still pointing in the same direction in space, but it's now going through a different part of the surface (if I understood correctly).
I never said they were incompetent, just that I didn't understand.
Meanwhile, after skimming through the original paper, I figured out that the actual axis of rotation (the vector of angular momentum) hasn't changed. The surface has just realigned itself. So even though the axis of rotation is still angled the same way relative to Pluto's orbit around the sun, there are now different bits of the surface at the poles. That makes a lot more sense.
(Yes, tidal effects do tend to affect spins, like causing tidal lock, and in fact Pluto and Charon are tidally locked, but that's not what this is about).
After having given the actual original article a quick 3 minute read, I was just coming back here to post exactly that. Pluto's axis of rotation hasn't changed, its surface has just reoriented itself so that different bits of the surface are at the poles.
It's as if you would move the surface of the earth around so that Belgium is at the north pole, The planet would still be spinning around an axis angled 23.4 from "vertical" relative to its orbit around the sun, but the map of the earth would look different. And it would be a hell of a lot colder here.
I don't think that's quite accurate. It is true that objects may line themselves up with the direction of the gravitational gradient, but not because the heaviest part wants to be closer. It may well end up pointing exactly the other way. Take an ordinary stick in orbit, for example. If it is lined up with the gravitational vector, its lowest end will be attracted to the body more than its further end. If it turns slightly away from vertical, the tidal force will tend to bring it back to vertical because gravity is still pulling the lowest end more strongly. The weights don't really matter, you may have a stick with a heavy end pointing away from the planet and it will be perfectly stable that way (the heavy bit receives less pull if it's further away and therefore tends to stay away from the planet).
Anyway, tidal forces are indeed responsible for things like tidal locking of the moon (where the moon's slowing down was compensated by a change in its orbital distance and smaller effects on the axial rotation of the earth) but I don't see how it can tilt the rotational axis of a planet. Certainly the sun's tidal force at that distance is nowhere nearly strong enough, or is it?
I'm not saying those scientists are wrong, by the way. Just that it needs to be explained properly because the simplified explanation does not make sense.
Well, no, that doesn't happen. You can spin faster and slower by moving mass closer to the axis and further out (like an ice skater stretching her arms), but you can't change the total rotational momentum (which remains constant in the ice skater example) nor its direction without an external force. That external force, in this case, is probably gravity (and more particularly tidal forces since a constant gravitational force does not cause rotations). I'm just having trouble understanding how it can tip the axis of an entire planet.
But with flywheels, the momentum does not disappear. You make the spacecraft turn one way by spinning the flywheel the other way. The total momentum remains the same. Due to all sorts of forces trying to make a spacecraft turn (slight drag from fringes of atmosphere, tidal forces, even forces caused by light), the momentum from all those corrections builds up in the flywheel and they have to get rid of it with special momentum dumping procedures, for example with thrusters or using electromagnets against the earth's magnetic field. It's not that simple, momentum doesn't just go away. Certainly not by moving some mass around, otherwise that's what the sattellites would do. You can speed up the rate of rotation by bringing mass closer to the axis (like an ice skater) but the momentum remains the same and you can't just decide to start spinning around a different axis without some kind of external force.
Also, there's a big difference between changing orientation and changing the speed of rotation. Making a spacecraft turn to point in a different direction is simple. But if it's spinning in one direction and you want to make it spin in a different direction, it's quite a bit more complicated.
Seems to make sense, except for the fact that there's no up and down in space. Pluto is only experiencing significant gravity from the sun and from its largest moon Charon. So I'm having trouble understanding just what forces made it "tip over". What happened to conservation of momentum? You can't just make something spin in a different direction by shifting its mass around a little, unless some external force is involved. Was it tidal forces from Charon? That would mean the rotational momentum was transfered to Charon in some way, altering its orbit or its axis of rotation. How did that work?
Would love to hear more details if anyone understands what actually (supposedly) happened.
Gas cars are exempt because we have to support the oil economy.
Next up: a mandatory delay between the application of the accelerator and the response from the electric motor. All in the name of safety. And charging at home will be forbidden.
So what's the actual number of people hurt by very slow electric cars, that they based this estimate on? If it's such a major problem, with all the electric cars on the road today, there must be hundreds of cases, right? Dozens? OK, maybe one?
I almost got run over the other day by a guy backing up his Chevy Volt.
Fixed that for you, added emphasis.
There are lots of reports from people being startled by a slow electric car, but how many people have actually been hurt this way? And how many people have been hurt by gasoline cars backing up? The sound doesn't make one bit of difference in the number of casualties. No matter what the baseless "estimates" say.
What does make a difference, is backup cameras. They are becoming standard on more and more cars. But please, there's enough car noise already, why can't we finally get some quiet cars?
I'm in favour of a courtesy horn for pedestrians, like a polite version of the regular horn. That's all you need. You're not going to kill anyone at 5 mph, there's no need for ubiquitous synthesized car sounds now that we can finally have quiet cars.
I've heard lots of stories of people being startled by electric cars, in fact it happened to me once, but I have yet to hear of a single case of someone being injured because he didn't hear an electric car. And there are a couple of hundred thousand electric cars on the road already. If it really was such a problem, there would have been a few actual accidents by now.
It's just a minor annoyance for the driver, not a safety hazard.
Oh my, how is your recovery coming along? I mean, you must have been seriously hurt, right? Are your regular therapy sessions working for you?
What's that you say? Gasp... you were not hurt at all? The car was driving so slowly that you couldn't hear it, yet, it did not hurt you? How can that possibly be?
Then make the pedestrians wear a sound emitting device around their necks so we can hear them. After all, they are the cause of the problem.
My wife used to have a Prius, and when she drove off early in the morning while I was still in bed with the window open, I could barely hear her leave. Finally we have quiet cars, and now the "think of the children" crowd wants to make them make noise and wake everyone up. More noise than some gasoline cars, by the way. All to avoid a few idiots being startled (not hurt, mind you, because the car isn't going fast enough to hurt you if you can't hear it) during the short transition period it would take for them to get used to quiet cars. We'll have noisy cars for decades to come, with no chance of them becoming quieter since the minimum decibel level is mandated.
No, it's not a problem. By now we already have hundreds of thousands of electric cars on the road. How many people have actually been injured by one at low speed?
Startled, yes, that can happen. Happened to me once, I admit. "Oops, there's a car, sorry!". End of story. When a car is traveling fast enough to hurt you, it's fast enough for you to hear it. Even the noise fans agree it's only a "problem" at low speed, but at those speeds there is no problem because the driver can stop on a dime.
At low speed, the only kind of dangerous accidents that happen relatively regularly is parents backing over their toddlers in the driveway with gasoline cars. Obviously the engine noise didn't help in those cases, and neither will a speaker. Backup cameras are a much better solution there, and they are becoming standard on more and more cars.
And what about Rolls Royces or high end Mercedeses with engines so quiet you don't hear them idling? Why do they get a pass? We're now arriving at the ridiculous situation where electric cars will be making more noise than gasoline powered cars. But maybe that was the idea all along. Can't have those electric cars taking jobs away from oil pumpers, can we? Next thing you know, they'll mandate a delay between the application of the accelerator pedal and the reaction of the motor. And maybe add hiccups during acceleration to mimick gear changes.
I was once startled by an electric car creeping up on me. I went "oh, oops, there's a car". That was all, no ambulance required, I didn't even need psychologic counseling.
With hundreds of thousands of electric cars on the road today, just how many people have actually been injured by one because they didn't hear it? No "estimates" please, has anyone on this planet actually been hurt by one at low speed?
If it's fast enough to hurt you, it's fast enough to be heard. If you can't hear it, it might startle you but that's it. No need to mandate noise in our quiet street. Maybe add a courtesy alert, like a polite version of the car horn, to warn pedestrians when they're in your way. That would be nice. But now that we can finally have quiet cars, it's total lunacy to mandate them to make noise.
How about this better idea: why don't we mandate that all pedestrians wear a noise emitting gizmo around their neck so that drivers of electric cars can hear them?
I wouldn't say the solving part is trivial. It looks like it's solving it in around 20 moves, very close to the theoretical minimum. The solution you linked to doesn't come anywhere near that efficiency, it already needs well over 20 moves just for the first layer. Coming up with extremely short solutions does require an enormous amount of computing.
I do agree that it's nothing like driving a car: those AIs use neural networks that look for approximate solutions based on fuzzy data. Completely different from the exact mathematical problem that is a Rubik's cube. This is just a viral ad to get name recognition, unrelated to their actual technology.
I remember a question on a physics exam many years ago where someone claimed to have seen a green light due to the doppler effect and you had to calculate the fine for speeding.
You have to admire their audacity, though. Why write viruses and trojans if you can just ask people to use your "service" voluntarily? And they actually do sign up for it! Absolutely brilliant idea.
Slashdot Mirror
A rocket becomes lighter as it gains speed. Therefore, if you would convert its final kinetic energy (lots of speed times much less mass) back to usable energy again, you would end up with less than what you spent to get it (and much of its fuel) up to speed.
The EM drive, though, keeps the same mass. That means that, assuming force and energy consumption remain the same at any velocity, at some point you indeed start to create more kinetic energy than you put in.
Sure, something else must be wrong. But that's not it.
That's what Mexicans often yell during hunting season in the state of New York. "Donald! Duck!".
You are quite right about tidal effects causing precession, and your links were very informative, but meanwhile I figured out that this is not what the actual paper was about.
Yes, Pluto and Charon are tidally locked because of the mechanisms you described. That happened very long ago.
However, more recently, the redistribution of mass on Pluto's surface caused the whole surface to realign itself with the axis of rotation (which did not change). So Pluto's axis did not tilt (at least not due to the described effect), it's still pointing in the same direction in space, but it's now going through a different part of the surface (if I understood correctly).
I never said they were incompetent, just that I didn't understand.
Meanwhile, after skimming through the original paper, I figured out that the actual axis of rotation (the vector of angular momentum) hasn't changed. The surface has just realigned itself. So even though the axis of rotation is still angled the same way relative to Pluto's orbit around the sun, there are now different bits of the surface at the poles. That makes a lot more sense.
(Yes, tidal effects do tend to affect spins, like causing tidal lock, and in fact Pluto and Charon are tidally locked, but that's not what this is about).
After having given the actual original article a quick 3 minute read, I was just coming back here to post exactly that. Pluto's axis of rotation hasn't changed, its surface has just reoriented itself so that different bits of the surface are at the poles.
It's as if you would move the surface of the earth around so that Belgium is at the north pole, The planet would still be spinning around an axis angled 23.4 from "vertical" relative to its orbit around the sun, but the map of the earth would look different. And it would be a hell of a lot colder here.
If they can see Russia from their house, surely they can connect to their internet?
I don't think that's quite accurate. It is true that objects may line themselves up with the direction of the gravitational gradient, but not because the heaviest part wants to be closer. It may well end up pointing exactly the other way. Take an ordinary stick in orbit, for example. If it is lined up with the gravitational vector, its lowest end will be attracted to the body more than its further end. If it turns slightly away from vertical, the tidal force will tend to bring it back to vertical because gravity is still pulling the lowest end more strongly. The weights don't really matter, you may have a stick with a heavy end pointing away from the planet and it will be perfectly stable that way (the heavy bit receives less pull if it's further away and therefore tends to stay away from the planet).
Anyway, tidal forces are indeed responsible for things like tidal locking of the moon (where the moon's slowing down was compensated by a change in its orbital distance and smaller effects on the axial rotation of the earth) but I don't see how it can tilt the rotational axis of a planet. Certainly the sun's tidal force at that distance is nowhere nearly strong enough, or is it?
I'm not saying those scientists are wrong, by the way. Just that it needs to be explained properly because the simplified explanation does not make sense.
Well, no, that doesn't happen. You can spin faster and slower by moving mass closer to the axis and further out (like an ice skater stretching her arms), but you can't change the total rotational momentum (which remains constant in the ice skater example) nor its direction without an external force. That external force, in this case, is probably gravity (and more particularly tidal forces since a constant gravitational force does not cause rotations). I'm just having trouble understanding how it can tip the axis of an entire planet.
But with flywheels, the momentum does not disappear. You make the spacecraft turn one way by spinning the flywheel the other way. The total momentum remains the same. Due to all sorts of forces trying to make a spacecraft turn (slight drag from fringes of atmosphere, tidal forces, even forces caused by light), the momentum from all those corrections builds up in the flywheel and they have to get rid of it with special momentum dumping procedures, for example with thrusters or using electromagnets against the earth's magnetic field. It's not that simple, momentum doesn't just go away. Certainly not by moving some mass around, otherwise that's what the sattellites would do. You can speed up the rate of rotation by bringing mass closer to the axis (like an ice skater) but the momentum remains the same and you can't just decide to start spinning around a different axis without some kind of external force.
Also, there's a big difference between changing orientation and changing the speed of rotation. Making a spacecraft turn to point in a different direction is simple. But if it's spinning in one direction and you want to make it spin in a different direction, it's quite a bit more complicated.
Seems to make sense, except for the fact that there's no up and down in space. Pluto is only experiencing significant gravity from the sun and from its largest moon Charon. So I'm having trouble understanding just what forces made it "tip over". What happened to conservation of momentum? You can't just make something spin in a different direction by shifting its mass around a little, unless some external force is involved. Was it tidal forces from Charon? That would mean the rotational momentum was transfered to Charon in some way, altering its orbit or its axis of rotation. How did that work?
Would love to hear more details if anyone understands what actually (supposedly) happened.
And what data is this estimate based on?
Also, those 125,000 pedestrians and bicyclists are not all injured at less than 20 mph. The vast majority are at much higher speeds.
So no, it's not a problem.
Gas cars are exempt because we have to support the oil economy.
Next up: a mandatory delay between the application of the accelerator and the response from the electric motor. All in the name of safety. And charging at home will be forbidden.
I've stopped students from walking into the path of buses.
Don't tell anyone, or inevitably somebody will get the idea that buses aren't quite loud enough.
So what's the actual number of people hurt by very slow electric cars, that they based this estimate on? If it's such a major problem, with all the electric cars on the road today, there must be hundreds of cases, right? Dozens? OK, maybe one?
I almost got run over the other day by a guy backing up his Chevy Volt.
Fixed that for you, added emphasis.
There are lots of reports from people being startled by a slow electric car, but how many people have actually been hurt this way? And how many people have been hurt by gasoline cars backing up? The sound doesn't make one bit of difference in the number of casualties. No matter what the baseless "estimates" say.
What does make a difference, is backup cameras. They are becoming standard on more and more cars. But please, there's enough car noise already, why can't we finally get some quiet cars?
And a button for a neighing sound!
OK, I changed my mind, mandatory sounds are a good idea! I'd love to have a Tesla that sounds like horse's hooves.
I'm in favour of a courtesy horn for pedestrians, like a polite version of the regular horn. That's all you need. You're not going to kill anyone at 5 mph, there's no need for ubiquitous synthesized car sounds now that we can finally have quiet cars.
I've heard lots of stories of people being startled by electric cars, in fact it happened to me once, but I have yet to hear of a single case of someone being injured because he didn't hear an electric car. And there are a couple of hundred thousand electric cars on the road already. If it really was such a problem, there would have been a few actual accidents by now.
It's just a minor annoyance for the driver, not a safety hazard.
Oh my, how is your recovery coming along? I mean, you must have been seriously hurt, right? Are your regular therapy sessions working for you?
What's that you say? Gasp... you were not hurt at all? The car was driving so slowly that you couldn't hear it, yet, it did not hurt you? How can that possibly be?
Then make the pedestrians wear a sound emitting device around their necks so we can hear them. After all, they are the cause of the problem.
My wife used to have a Prius, and when she drove off early in the morning while I was still in bed with the window open, I could barely hear her leave. Finally we have quiet cars, and now the "think of the children" crowd wants to make them make noise and wake everyone up. More noise than some gasoline cars, by the way. All to avoid a few idiots being startled (not hurt, mind you, because the car isn't going fast enough to hurt you if you can't hear it) during the short transition period it would take for them to get used to quiet cars. We'll have noisy cars for decades to come, with no chance of them becoming quieter since the minimum decibel level is mandated.
A sad day for people who like peace and quiet.
No, it's not a problem. By now we already have hundreds of thousands of electric cars on the road. How many people have actually been injured by one at low speed?
Startled, yes, that can happen. Happened to me once, I admit. "Oops, there's a car, sorry!". End of story. When a car is traveling fast enough to hurt you, it's fast enough for you to hear it. Even the noise fans agree it's only a "problem" at low speed, but at those speeds there is no problem because the driver can stop on a dime.
At low speed, the only kind of dangerous accidents that happen relatively regularly is parents backing over their toddlers in the driveway with gasoline cars. Obviously the engine noise didn't help in those cases, and neither will a speaker. Backup cameras are a much better solution there, and they are becoming standard on more and more cars.
And what about Rolls Royces or high end Mercedeses with engines so quiet you don't hear them idling? Why do they get a pass? We're now arriving at the ridiculous situation where electric cars will be making more noise than gasoline powered cars. But maybe that was the idea all along. Can't have those electric cars taking jobs away from oil pumpers, can we? Next thing you know, they'll mandate a delay between the application of the accelerator pedal and the reaction of the motor. And maybe add hiccups during acceleration to mimick gear changes.
Or maybe something more nostalgic like this:
https://www.youtube.com/watch?...
I don't get what the big problem is either.
I was once startled by an electric car creeping up on me. I went "oh, oops, there's a car". That was all, no ambulance required, I didn't even need psychologic counseling.
With hundreds of thousands of electric cars on the road today, just how many people have actually been injured by one because they didn't hear it? No "estimates" please, has anyone on this planet actually been hurt by one at low speed?
If it's fast enough to hurt you, it's fast enough to be heard. If you can't hear it, it might startle you but that's it. No need to mandate noise in our quiet street. Maybe add a courtesy alert, like a polite version of the car horn, to warn pedestrians when they're in your way. That would be nice. But now that we can finally have quiet cars, it's total lunacy to mandate them to make noise.
How about this better idea: why don't we mandate that all pedestrians wear a noise emitting gizmo around their neck so that drivers of electric cars can hear them?
I wouldn't say the solving part is trivial. It looks like it's solving it in around 20 moves, very close to the theoretical minimum. The solution you linked to doesn't come anywhere near that efficiency, it already needs well over 20 moves just for the first layer. Coming up with extremely short solutions does require an enormous amount of computing.
I do agree that it's nothing like driving a car: those AIs use neural networks that look for approximate solutions based on fuzzy data. Completely different from the exact mathematical problem that is a Rubik's cube. This is just a viral ad to get name recognition, unrelated to their actual technology.
I remember a question on a physics exam many years ago where someone claimed to have seen a green light due to the doppler effect and you had to calculate the fine for speeding.
You have to admire their audacity, though. Why write viruses and trojans if you can just ask people to use your "service" voluntarily? And they actually do sign up for it! Absolutely brilliant idea.