It wasn’t bad journalism. When I got to the end of the article, I found myself wanting to know more. I wanted to hear more about the way it worked. I wanted to hear more backstory on Sherlock and his mathematically inclined Dr. Watson. I wanted to hear if there’d been a comparison to the EmDrive or the other ones, and what his opinions are on those other ideas. There wasn’t anything beyond minor spelling flaws in this article! Ignore the pedants. Everybody’s looking for a takedown. There are no stupid comments, only stupid people. Your article was fine. Write more of them, so I can read 'em.
5 Likes
What is the box pushing against when it slows down?
The air in the cylinder.
What is the air in the cylinder pushing against?
The bottom of the cylinder.
To slow down the box you must exert a force. The force has to come from the cylinder. So it doesn’t matter if the box is colliding with the bottom of the cylinder or slowing down by a parachute or by induction or anything else. The force slowing down the cylinder is the same.
2 Likes
Prove it please!
It’s not actually the same as the Mass-Energy Equivalence. It’s a specific interpretation of Mach’s conjecture, that says that transient mass fluctuations arise in any object that absorbs internal energy while undergoing acceleration.
So if you have a battery and a capacitor, charging and discharging the capacitor doesn’t have any effect on the mass. But (according to the hypothesis), if you also accelerate the capacitor while you are charging and discharging it, then you get these transient mass changes.
1 Like
Admin note: deleted most of the inane tangential dickwaving about science journalism, including replies, etc. Stay on topic.
4 Likes
Fine. I just thought that was the topic.
1 Like
Sorry scav. Your post was auto-forwarded to my email address, and I was all set to discuss the issue that you raised, but I guess the Managing Editor knows inane dickwaving when she sees it.
1 Like
He does look a bit like a woman in his avatar, it’s true, but I think he’s actually going for “drunk elf.”
7 Likes
Thanks. It sucked.
Actually, he says that he uses piezoelectric actuators running at 20 kHz. This is not new technology - it’s the same thing that was used in the crappy crystal radio earphone I had as a kid 40 years ago. The new thing is the accelerometer used to measure the phase of the vibration.
Hi samsam
You say:
What is the box pushing against when it slows down?
The air in the cylinder.
What is the air in the cylinder pushing against?
The bottom of the cylinder
That is absolutely true, when the box is in a tight fit (like a piston in its cylinder), if we increase the size of the container (so it’s not a tight fit anymore) some of the air will move around the box and not push against the bottom (or far end of the cylinder).
If the container is large enough most of the “push against the bottom of
the cylinder” you are visualizing will be dispersed.
If you smoke, try to blow smoke to a far wall, it will chaotically turn into a cloud that is not going to exert any pressure.
If you blow smoke thru a tube, it will reach the wall no matter how far because the tube keeps the flow of molecules laminar. (The container must be large enough so a turbulent flow is allowed)
If you throw
a stone to a far wall (and hit it) you will transmit most of the force because
you a throwing a group of bound molecules.
If they are not bound (or solid) they will be diverted by the air molecules that get in its way.
No, really. The box has to be exerting a force against the air in the direction of the bottom of the cylinder, by Newton’s 3rd law. This has to create an acceleration of air molecules in the direction of the bottom of the cylinder. This means we must have particles with an increased velocity in the direction of the bottom of the cylinder, so we must have increased their momentum in that direction. This momentum of molecules in the direction of the cylinder can’t be “dispersed” to some other angle – the momentum of a system in a specific direction has to be maintained through all collisions.
Really, the system you describe is using nothing but Newtonian physics. You’re really not going to break the Law of Conservation of Momentum in such a trivial case, or it wouldn’t be a law at all.
Draw a free-body diagram if you’re unsure.
In the mean time, answer this: if a bird in a box (as big a box as you want) flaps up so his head is pressed against the top of the box, and flaps really hard, why doesn’t the box go up? There is a force upwards on the box (the bird’s head), and the force downwards is just magically “dispersed” right? So it should go up, right? Why don’t we just power a spaceship with a box of air and some birds (maybe mechanical birds) in it?
Edit: I now see you’re the creator of that video. Right here (6:21), you breaking Newton’s Third Law, and failing to draw a correct free-body diagram. You show a force acting against the object, but where is the equal-and-opposite force? F(A) is a magic force?
2 Likes
P.S. If you can change the mass in a closed system, of course constant momentum over greater or lesser mass would imply lesser or greater speed, and constant kinetic energy over greater or lesser mass would imply greater or lesser speed, but momentum is linear and kinetic energy is quadratic, so I’m not sure how you could conserve both momentum and kinetic energy if you change the mass. I suppose if the excess kinetic energy is lost to heat, and then replenished from some other source of energy each cycle, then you could conserve both momentum and total energy
Imagine a bowling ball and a balloon connected by an extendable piston, floating in space. When the piston extends, the balloon will move further than the bowling ball, by conservation of momentum.
This is the same reason than a large spaceship can extend a small probe, and the spaceship itself will only slightly move backwards.
When the piston retracts, the balloon yet again will move more, and you’ll end up back at the same place.
Now, while the arm is extended, if you magically switch the weight of the bowling ball and the balloon (note: not “transfer” the weight by any normal means, because this weight-transfer itself will move the balls), now when you retract the arm the now-very-light bowling ball will be the one to move. So you won’t have ended back where you were, you’d end up slightly displaced.
3 Likes
Disclaimer, I have a PhD in Physics, been working in academia for almost two decades now.
The article is not clearly written for the technically-oriented reader. Too much philosophy and not enough physics and technical details. If I understand what it written, then it looks like they propose to vary the mass by expending energy, probably based on the fact that e=m c^2 ? If they could do that in a way that that does not affect the momentum of the rest of the system, then the propulsion principle would work.
However, it is not clear at all from this article how exactly they will be changing the mass, and which underlying principle they will be using. The example with the capacitor and electric charge makes no sense to me. Another question is, suppose they figure a way to quickly change the mass of an object; then they would still need to make sure that this change in no way affects the momentum of the rest of the system. Those are just some of the most obvious questions that come to my mind, but of course there is more… For example, lets say they managed to quickly change the mass of the box A by using energy, but then the mass of the spaceship (or box B) would have also changed, since e=mc^2. Not enough information here about what they are proposing to do, so I could go on speculating
I should probably need to read the original papers by the inventor before commenting here, but looks like that would be a waste of time, judging from what I have read here at least.
1 Like
I thought the article mentioned that when a capacitor is charged, its mass decreases momentarily.
Yes, but why did the mass change? And if it change, did the change affect the momentum of the rest of the system? There are many ways to change the mass of capacitor, but I am not sure I understand their explanation (they talk about action at a distance???)
1 Like
Honestly, don’t know. I’m not a physicist with a PhD. I took it on face value that the mass changes when you electrify something. Why? How does toast toast? I really have no clue, but it’s YUMMY with butter and jam.
In a universe containing only one particle, what kind of reference frame do you have in mind? You say it’s not the absolute reference frame you’d get from the aether or any other conception of “the fabric of space”; so the reference frame you’re talking about can’t be a property of the universe. Clearly it’s not the reference frame of the particle. So what is the third option you are suggesting?
There’s some evidence that time is an emergent property of quantum entanglement, and quantum gravity seems to be suggesting that spacetime is an emergent property. If both time and space are emergent properties of quantum events, then velocity isn’t a fundamental part of our universe.
So I’m not saying you’re wrong, but it’s a lot less settled than you seem to believe.
