506 réponses à ce sujet

[o Ventus]

This also doesn't take in consideration the pressure that would be exerted on any "underwater colony". It's also why humans can't dive below a certain depth.

 

Hopefully, someone more knowledgeable in physics will elaborate further.

Pressure is, for all intents and purposes, just another way to say "weight", so pressure is really more just a measure of how heavy the water is. Cold water is heavier than warm water because colder water is more dense (though really at depths approaching the sea floor, the water will be freezing cold anyway). 

 

At freezing temperature (0 Celsius or 32 Fahrenheit), water has a density of 1.94 slugs per cubic foot (round up to 2 for the sake of simplicity) and a weight of around 62.5 pounds (the pounds --> kilograms conversion ratio escapes me). If we're talking about the floor of the Pacific Ocean (36,000 feet below sea level) and assuming the density and temperature of the water stays constant all the way down, I would hazard a guess that the water would weigh.... Maybe 1.125 million pounds per cubic foot. The actual number would be lower since the water closer to the surface is warmer and therefore less dense (so take off maybe a couple tens of thousands of pounds), and this is just with some quick math (and I'm not the greatest mathematician, so take my results with a grain of salt).

[Eternal Phoenix]

There is no difference between how science and other "knowledge" -systems works psychologically or semantically. The difference is in the rather strict discipline that science adheres to, which produces and serves the reliability of the map. Religions, astrology, UFO-logy, New Age etc, are also just maps. They are human fantasies one can have knowledge about, but these systems themselves do not contain any knowledge. Those are fantasy lala-lands, because their systems lack the rules and discipline to discern knowledge from fantasies.

 
None of those things are "other" knowledge systems. Astrology is a pseudo-scientific subject, UFOlogy is the same and religions are just a set of beliefs anyone can make and combine (see Unitarian Universalism). Religion is not science whereas astrology and UFOlogy dress themselves up as science (with the former once being considered scientific centuries ago) but are really pseudo-science and now refuted completely. Astrology and UFOlogy both don't adhere to falsifiability or scientific method whereas the sermon on the mount or Nyāya doesn't require these two things since these are moral and philosophical teachings respectively (being religious subjects from Christianity and Hinduism).

[bEVEsthda]

Pressure is, for all intents and purposes, just another way to say "weight", so pressure is really more just a measure of how heavy the water is. Cold water is heavier than warm water because colder water is more dense (though really at depths approaching the sea floor, the water will be freezing cold anyway). 

 

No. Pressure is not weight. Not at all. The weight of the water above causes the pressure under water. Just like the weight of the air causes our atmosphere pressure. But pressure is a different, distinct physical property. Weight is a product of mass and acceleration (gravity), and thus a force. Something else. Pressure is not force.

 

One thing is that pressure, just like temperature, influence chemical processes and equilibrium. This is the reason why the human body gets into various problems deep underwater. The partial Oxygen pressure has to be kept low, or we'll have Oxygen-poisoning. Next, the partial Nitrogen pressure has to be kept low, or we'll have Nitrogen-poisoning. Diving deeper than 30m with a Nitrogen-Oxygen mix is strictly for experienced divers. Diving deeper than 60m, on N-O, is lethally dangerous even for very experienced divers. Dives as deep or deeper than 90m, on N-O, are rare and typically sprinkled with deaths. To go deeper, an extremely nonreactive and light gas is used to lower the Oxygen pressure, Helium.

Pressure continues to affect other chemical processes in our bodies though. I'm not aware of the current record, but those experiment I know of since earlier, seem to indicate that the body&mind start to get into serious trouble below 600m.

[bEVEsthda]

 
None of those things are "other" knowledge systems. Astrology is a pseudo-scientific subject, UFOlogy is the same and religions are just a set of beliefs anyone can make and combine (see Unitarian Universalism). Religion is not science whereas astrology and UFOlogy dress themselves up as science (with the former once being considered scientific centuries ago) but are really pseudo-science and now refuted completely. Astrology and UFOlogy both don't adhere to falsifiability or scientific method whereas the sermon on the mount or Nyāya doesn't require these two things since these are moral and philosophical teachings respectively (being religious subjects from Christianity and Hinduism).

 

Which is obviously why I didn't write knowledge systems, but "knowledge" -systems.

[o Ventus]

No. Pressure is not weight. 

"For all intents and purposes [...]"

 

 

 

 

for all intents and purposes

 

(prepositional phrase; idiomatic, US) For every functional purpose; in every practical sense; in every important respect; practically speaking.

 

edit: I don't know why I can't put the above 2 lines of text into the same quote block.

[Fast Jimmy]

There are plenty of absolute truths. They're called "laws."

And what's funny is that the EM Drive is appearing to violate one of those - the Law of Conservation of Energy.

No, it didn't. The EM drive has been speculated to be a thing ever since (at least) 2001, as per NASA themselves. Only now are they making the thing work. It isn't as if we just discovered some new fundamental truth of the universe. We already have the established principles of how the EM drive works and the forces at play:

Dr. White proposed that the EM Drive’s thrust was due to the Quantum Vacuum (the quantum state with the lowest possible energy) behaving like propellant ions behave in a MagnetoHydroDynamics drive (a method electrifying propellant and then directing it with magnetic fields to push a spacecraft in the opposite direction) for spacecraft propulsion. In Dr. White’s model, the propellant ions of the MagnetoHydroDynamics drive are replaced as the fuel source by the virtual particles of the Quantum Vacuum, eliminating the need to carry propellant.

Yes, but the null test of this week's experiments have invalidated the Quantum Vacuum theory as the source of the EM Drive's thrust. So, at this time, no one has a credible theory about it is even working now. Which makes this extremely interesting.

[LPPrince]

And what's funny is that the EM Drive is appearing to violate one of those - the Law of Conservation of Energy.

 

Which is why I say that science is more about humans trying to make sense of everything/existence(which ebbs and flows and changes with more information/different understanding) than absolute facts. Cause if it was about absolute facts that couldn't change, we'd still think Earth was flat and everything revolved around it.

 

But anyway back to the EM Drive- Got any theories Jimmy? Besides the spacetime distortion. Cause I got nothing. AND THIS IS SO COOL

[Gravisanimi]

My theory basically.

 

Not space-time distortion, but similarly, space-time harmonics.

 

Basically the idea is that it causes particles to... well...

 

See it's based on String Theory.

 

It causes particles to resonate to the approximate frequency these Strings use to expand the universe, kinda how like a sound vibration moves across the room.

 

Itself isn't causing the distortion, it's just kinda lazily riding the waves the universe is already making.

 

Of course I have nothing to back this up and not nearly large enough of a background in physics to back it up, but that's my shot in the dark.

[LPPrince]

My theory basically.

 

Not space-time distortion, but similarly, space-time harmonics.

 

Basically the idea is that it causes particles to... well...

 

See it's based on String Theory.

 

It causes particles to resonate to the approximate frequency these Strings use to expand the universe, kinda how like a sound vibration moves across the room.

 

Itself isn't causing the distortion, it's just kinda lazily riding the waves the universe is already making.

 

Of course I have nothing to back this up and not nearly large enough of a background in physics to back it up, but that's my shot in the dark.

 

Lamia avatar so its okay

[Gravisanimi]

Lamia avatar so its okay

Don't mind Prince he's just happy I have an avatar he can recognize for once.

[LPPrince]

Don't mind Prince he's just happy I have an avatar he can recognize for once.

 

 Solid hypothesis

[Sigma Tauri]

No. Pressure is not weight. Not at all. The weight of the water above causes the pressure under water. Just like the weight of the air causes our atmosphere pressure. But pressure is a different, distinct physical property. Weight is a product of mass and acceleration (gravity), and thus a force. Something else. Pressure is not force.

 

I don't think they're that distinct at all. Pressure is weight per unit of area. I mean look at this formula

 

Pressure = density x gravitational constant x height

 

It already accounts force since density = mass/volume and gravitational constant is acceleration near the Earth's surface.

[GMagnumm]

aye dam i culd use dis 2 warp 2 da front of da drive thru at wendys at lunch tim wen da line hella long tbh

[bEVEsthda]

I don't think they're that distinct at all. Pressure is weight per unit of area. I mean look at this formula

 

Pressure = density x gravitational constant x height

 

It already accounts force since density = mass/volume and gravitational constant is acceleration near the Earth's surface.

 

??  The fact that two different, distinctly different, physical quantities can be used in the same formula doesn't make them the same.

Energy, for instance, is not displacement (length). Despite that Energy can be expressed as = mass * displacement^2 / time^2.

 

Pressure is measured as force/area. That is correct. But neither Pressure, nor Force, weight or Area are base quantities. They're all derived. If that is your criteria for "distinct", none of them are.

 

 

 

"For all intents and purposes [...]"

 

(prepositional phrase; idiomatic, US) For every functional purpose; in every practical sense; in every important respect; practically speaking.

 

edit: I don't know why I can't put the above 2 lines of text into the same quote block.

 

 

 I do understand how you think, in this case, with pressure in the depth of an ocean.

 

But in general terms, they're two different quantities, measured in different units.  And Weight is a special case of Force, and Force is a vector. Pressure is a scalar quantity.

 

You have pressure in a steam engine, you have pressure in the combustion chamber of a gas turbine, You have pressure in a Tokamak. Where and how, in any of these cases, comes weight into the picture?

[Fast Jimmy]

Which is why I say that science is more about humans trying to make sense of everything/existence(which ebbs and flows and changes with more information/different understanding) than absolute facts. Cause if it was about absolute facts that couldn't change, we'd still think Earth was flat and everything revolved around it.

But anyway back to the EM Drive- Got any theories Jimmy? Besides the spacetime distortion. Cause I got nothing. AND THIS IS SO COOL

I'm coming up empty. But while physics is insanely interesting to me, but grasp on its more complex aspects is definitely something out of my element. So I'll let others who are better versed in the subject discuss possible theories... I'll just be over in the corner praying for FTL.

[LPPrince]

I'm coming up empty. But while physics is insanely interesting to me, but grasp on its more complex aspects is definitely something out of my element. So I'll let others who are better versed in the subject discuss possible theories... I'll just be over in the corner praying for FTL.

 

The NASA Spaceflight forums have all the theories under the sun.

[mybudgee]

Closer to 70/80, and even then thats just when they begin to do stuff in space.

This is more for the next few generations than us.

I still want my damn jetpack!

[LPPrince]

I still want my damn jetpack!

 

Dream on, budgerigar

[leaguer of one]

We have the stars, baby!!!! We have the stars!!!!!

[Fast Jimmy]

The NASA Spaceflight forums have all the theories under the sun.

Yeah been lurking there for the past week now. Very interesting conversations going on.

[LPPrince]

Yeah been lurking there for the past week now. Very interesting conversations going on.

 

I've been lurking too. 

[Sigma Tauri]

??  The fact that two different, distinctly different, physical quantities can be used in the same formula doesn't make them the same.

Energy, for instance, is not displacement (length). Despite that Energy can be expressed as = mass * displacement^2 / time^2.

 

Pressure is measured as force/area. That is correct. But neither Pressure, nor Force, weight or Area are base quantities. They're all derived. If that is your criteria for "distinct", none of them are.

 

I think you missed my point entirely. The fact that the pressure formula uses base dimensions does not make them the same as those dimensions. It is a mistake to consider the conceptual equality of work to displacement as much as it would be pressure to mass, length, or time. The point is that the distinction between the Newton's second law and the pressure formula differs only by area (height/volume). What is in effect is still the same, pressure = (mass x acceleration)/area. Both pressure and force ultimately create the effect of movement, but pressure is more applicable in certain situations like the lumen of an artery because its effect is more disperse than a single vector.

 

Of course, that doesn't make them totally non-distinct concepts. Work and the different types of energies (kinetic, gravitational potential, elastic potential, chemical) are also distinct, but how you want to make that distinction is only important to what you're trying to discover, explain, or apply.

[TheBunz]

We probably won't see practical application of this technology for 100 years

[The Devlish Redhead]

My theory basically.

 

Not space-time distortion, but similarly, space-time harmonics.

 

Basically the idea is that it causes particles to... well...

 

See it's based on String Theory.

 

It causes particles to resonate to the approximate frequency these Strings use to expand the universe, kinda how like a sound vibration moves across the room.

 

Itself isn't causing the distortion, it's just kinda lazily riding the waves the universe is already making.

 

Of course I have nothing to back this up and not nearly large enough of a background in physics to back it up, but that's my shot in the dark.

 

 

 

It causes particles to resonate at the same resonance of the universe around it for want of a better word, and that causes the distortion..

 

Made me think of the ionic vacuum drive from the movie Titan A E