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Science Questions!!

#34
@Akbar2thegreat said in #33:
> Replying to one's own question seems interesting!
But it is! It is!

Just start by saying:

Who the hell do you think you are!?
The Spice Girls or something?

And then you're off!
#37
@Thalassokrator said in #22:

> Very basically because they don't touch the ground. An overhead power line might be at an electric potential difference of V = 500 kV relative to the ground (it can go as high as 1.1 MV). If the bird could touch both the power line and the ground at the same time, it would get electrocuted. Let's grant the bird an electrical resistance of R=500 Ω (electrical resistance of dry skin is 100 kΩ, that of wet skin is 1kΩ, but high voltage breaks down your skin, drastically lowering resistance). According to Ohm's law I = V/R, so the bird would sustain a current of I = (500,000 V)/(500 Ω) = 1000 A, about a thousands amps and be burned to a crisp.
>
> However the bird does not touch the ground and both of its feet are therefore at the same electrical potential meaning that electrons have no reason to flow through the bird. See:
> engineering.mit.edu/engage/ask-an-engineer/how-do-birds-sit-on-high-voltage-power-lines-without-getting-electrocuted/
>
> It should also be noted that birds don't like to sit on (very) high voltage power lines, not because of electrical shocks but because the wire is still surrounded by strong electromagnetic fields which sometimes even move the bird's feathers back and forth (it's usually carrying three-phase electric power, so alternating current). You know this phenomenon from static electricity if you've ever rubbed a balloon against your hair. After having acquired a static electrical charge you can cause your hair to move by moving the balloon without touching the hair with the balloon. Quite spooky!
>
> Birds apparently find this unpleasant and therefore prefer to sit on the grounding wire which doesn't carry any electricity. Birds still die in the millions from overhead power lines by the way, just not because of the electricity but because they crash into them while flying at high speeds.

@FC-in-the-UK Your saviour failed you.
#38
@obladie said in #26:
> Place a cork in a bucket of water. Weight the cork with a fishing sinker suspended from the centre of the lower surface of the cork such that the top of the cork is level with the surface of the water.
> Now drop the whole system from a height of 6.3 metres.
> What happens to the cork? Does it rise, fall or stay the same in relation to the water-level?
That is a very complicated question that I'm not sure I will be able to answer correctly. To the best of my understanding, the cork should remain in the same level in relation to the water because the cork is a part of a system that should, in theory, have the same acceleration. I might be wrong as it has been a while since I have used kinematics.
#39
@TakeThePawnOrLose said in #37:
> @FC-in-the-UK Your saviour failed you.
@Thalassokrator if the wave length of the electric current was smaller than the distance between the feet of the bird, would the bird be electrocuted?
@TakeThePawnOrLose said in #38:
> That is a very complicated question that I'm not sure I will be able to answer correctly. To the best of my understanding, the cork should remain in the same level in relation to the water because the cork is a part of a system that should, in theory, have the same acceleration. I might be wrong as it has been a while since I have used kinematics.
I agree as long as we neglect the elasticity of water.
#40
@FC-in-the-UK said in #39:
> at Thalassokrator if the wave length of the electric current was smaller than the distance between the feet of the bird, would the bird be electrocuted?

Sorry that I didn't get around to answering you sooner. I hadn't checked on Lichess this past week, I hope my restarting of this thread will not inconvenience anyone.

I actually have to say that I'm initially not quite sure (although perhaps I ought to know). I'm not an electrical engineer. From my rudimentary understanding of electrodynamics and avian physiology I can say that whenever there's a nonzero electric potential difference, i.e. a voltage, the macroscopic approximation of Ohm's law should apply.
Therefore current should flow through a conducting material connecting the two points over which the potential difference is measured in proportion to the ratio between voltage (electrical potential difference) and electrical resistance of said material.

It should be noted that even air (usually a very bad conductor) can become ionised and conduct electricity across the spark gap at very high electric potential difference (=high voltage), so connecting doesn't necessarily mean touching. Never climb the roof of an electric tram or subway and NEVER EVER move your hand close to the overhead wire in any way! You'll die before you touch it.

Now, with a bird sitting on a electric power transmission line, it's my impression that unless the bird were to come into contact with the ground (having one foot somehow touching the ground (or sufficiently close to it as to ionise the air), the other still touching the power transmission line) no electric potential difference could be measured between the bird's feet. Electric power transmission lines use three-phase electric power, a form of alternating current: en.wikipedia.org/wiki/Alternating_current#Mathematics_of_AC_voltages

What I'm referring to in the above wiki article might be too simplistic to be applicable to the real world (I don't know, as I said I'm not an EE), but assuming that it is (even ignoring the three-phase part) I understand it to mean that AC voltages change only in time, not in space. Therefore I take it that an AC power line carrying an alternating current (and equally alternating although phase-shifted voltage) at a frequency of say 60 Hz will be at the same voltage (relative to the ground) everywhere along the wire at a particular moment in time. The AC doesn't seem to have a spatial "wavelength". Only a temporal one if you will. Which would be a sixtieth of a second in this case if I'm not mistaken (it's less weird to think in terms of frequency instead of wavelength here, I think).

The voltage between power line and ground changes 60 times a second, but is constant along the length of the wire at any moment in time (it's the same at every point along the wire). Therefore the frequency of the AC voltage and the distance between a bird's feet should not matter. The bird cannot be electrocuted while solely standing on a wire that's at the same voltage relative to the ground everywhere along its length. Both feet are at the same potential difference to the ground at any moment and therefore there's never any electric potential difference between the feet themselves and never any reason for current to flow through the bird.

At least that's my (possibly flawed) understanding.

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