Science questions not worth a thread I: I'm a moron!

[gay_Aleks]

Say, will wireless electricity ever be able to replace the current way we're transporting electricity (i.e, lots and lots of cables)?

 

[SS-18 ICBM]

"What would be needed to realistically bring life to a Golem, using any even tenuous parallel between placing a letter on its forehead and working with known phenomena studied in Physics?".

A robot activated by tactile feedback. Next.

 

[Tarquelne]

I came across a forum with a bunch of Venusian the other day. In an odd coincidence, they were discussing why helicopters won't work on Earth.

NASA - Helicopters on Mars

 

[timtofly]

So if the motor stops the blades keep turning, but without enough push back the helicopter will start to spin also?

 

[uppi]

Say, will wireless electricity ever be able to replace the current way we're transporting electricity (i.e, lots and lots of cables)?

No. There will be some special applications for wireless power, especially at very shot range. But for most of the electricity transport cables are much superior than what could ever be achieved by wireless power.

 

[brennan]

Say, will wireless electricity ever be able to replace the current way we're transporting electricity (i.e, lots and lots of cables)?

Not unless we can develop almost perfectly efficient ways of turning electrical energy into something else and back again, which seems unlikely.

Using long distance AC infrastructure we don't even move the electrons themselves, just provide an extended electric field. It's incredibly efficient.

 

[El_Machinae]

Wireless is really inefficient, because remember that it transmits as a sphere, or even if it's focused, it loses 'density' at the square of the distance traveled. It would then transmit as a cone. So, unless your receiver was giant, you lose a great portion of the energy put into the transmission.

I mean, we can think of some applications, but wires are just too awesome. You get some much distance out of them!

 

[Loppan Torkel]

They shouldn't. There's so little air, there would be nothing to push against.

There's also smaller drag. It could spin a lot faster given same energy and the rotors could be made of lightweight, folded material, like sails. ..and there's less gravitational force on Mars...

http://www.esa.int/Our_Activities/Technology/Dropship_offers_safe_landings_for_Mars_rovers

The dramatic conclusion to ESA’s latest StarTiger project: a ‘dropship’ quadcopter steers itself to lower a rover gently onto a safe patch of the rocky martian surface.

StarTiger’s Dropter project was tasked with developing and demonstrating a European precision-landing capability for Mars and other targets.

 

[Loppan Torkel]

So, it's clear cut? No choppers on Mars, or is this a case of assuming it because it's presumed?

 

[Cutlass]

There would have to be some other form of aerial transportation. Helicopters just aren't that efficient aerodynamically.

 

[Kyriakos]

Wireless is really inefficient, because remember that it transmits as a sphere, or even if it's focused, it loses 'density' at the square of the distance traveled. It would then transmit as a cone. So, unless your receiver was giant, you lose a great portion of the energy put into the transmission.

I mean, we can think of some applications, but wires are just too awesome. You get some much distance out of them!

Is that why wires are cylindrical? (due to the afforementioned tendancy of electrical currents to expand spherically?). Cause - as is known for around 2400 years now - Sphere+Cone=Cylinder, all of the same diameter.
Other way to form the question: why weren't wires built as right-angled parallelepipeda, etc (basically, instead of an extending sphere forming a cylinder, you would have an extending cube)

 

[Michkov]

I'd guess it has more to do with the way wires are produced rather than any advantage in geometry.

 

[uppi]

One probably could make the argument that surfaces are always messy, so the conductivity in the bulk might be higher than near the surface. That would mean that the surface compared to the cross section should be minimized, so you want a cylinder.

But I don't think the effect is big enough to notice for any wire of practically relevant size. Ease of fabrication is indeed the most important property of cylindrical wires.

 

[Cutlass]

I'm taking a lot of water to work to drink these days. Personally I think buying pre bottled water is an utter waste. So I bring a jug of it from home. But I got curious; how does the purity of my water stand up? I have a dehumidifier in the basement, and the water I'm using is condensed from the air. I expect there's a bit of dust in it, because the air in the basement is somewhat dusty. But overall how pure could I expect it to be?

 

[timtofly]

I'm taking a lot of water to work to drink these days. Personally I think buying pre bottled water is an utter waste. So I bring a jug of it from home. But I got curious; how does the purity of my water stand up? I have a dehumidifier in the basement, and the water I'm using is condensed from the air. I expect there's a bit of dust in it, because the air in the basement is somewhat dusty. But overall how pure could I expect it to be?

The point of distilling water is keeping it in a sealed container to keep it free from dust and bacteria that could be airborne. Most bottled water is not distilled, unless it states that it is distilled. Using a dehumidifier is a way to bring out water from the moisture in the air, how it is collected would be the issue. If it is allowed to be re-contaminated or not protected from bacteria growth which may be found in such conditions it would not be any different from tap water. A dehumidifier is not normally designed to produce drinking water due to the possible risks of microorganisms, airborne contaminants, and heavy metals such as copper and aluminum from the dehumidifier itself. If you had a way to boil that water and distill it, it would not be wasted, but then you could just run tap water through a filter as well. Even using the same container over and over without giving it the proper cleaning will eventually breed harmful bacteria.

I'd guess it has more to do with the way wires are produced rather than any advantage in geometry.

Wire is fabricated by "drawing" it through an opening. A drilled opening would have been the default method. I think it may have been possible to make a triangular opening or even an opening with more than 3 sides or surfaces. The default drilling method would be cylindrical. I wonder if any one has ever tested the efficiency of wire that is anything other than cylindrical?

 

[gay_Aleks]

What about wireless electricity that is only limited to a certain area?

For an example, the PC gets power from cable, but the peripherals would get power from wireless?

 

[El_Machinae]

Say, will wireless electricity ever be able to replace the current way we're transporting electricity (i.e, lots and lots of cables)?

'Optical fibre' made out of thin air

Milchberg and colleagues' made the equivalent of an optical fibre out of thin air by generating a laser with its light split into a ring of multiple beams forming a pipe.

They used very short and powerful pulses from the laser to heat the air molecules along the beam extremely quickly.

Such rapid heating produced sound waves that took about a microsecond to converge to the centre of the pipe, creating a high-density area surrounded by a low-density area left behind in the wake of the laser beams.

"A microsecond is a long time compared to how far light propagates, so the light is gone and a microsecond later those sound waves collide in the centre, enhancing the air density there," says Milchberg.

The lower density region of air surrounding the centre of the air waveguide had a lower refractive index, keeping the light focused.

"Any structure [even air] which has a higher density will have a higher index of refraction and thereby act like an optical fibre," says Milchberg

 

[Loppan Torkel]

I'm taking a lot of water to work to drink these days. Personally I think buying pre bottled water is an utter waste. So I bring a jug of it from home. But I got curious; how does the purity of my water stand up? I have a dehumidifier in the basement, and the water I'm using is condensed from the air. I expect there's a bit of dust in it, because the air in the basement is somewhat dusty. But overall how pure could I expect it to be?

Drinking too much distilled water isn't good for you in the long term since it seeps minerals out of your body (or so I've heard). I have no idea how potent this is or how pure your water gets, but just fyi..

edit: nvm, it seems fine to drink it...

 

[dusters]

How to explain string theory to 10 year old girl in less than 100 sentences?

 

[madviking]

http://www.reddit.com/r/explainlikeimfive/comments/20yui3/eli5_string_theory/cg87pu7