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A scientific fact/tidbit you recently learned that you thought was interesting

A car's stopping distance from 30mph is ~double the stopping distance from 20mph (Here in Wales the 'built up area' speed limit is about to be dropped from 30mph to 20mph, and a pamphlet delivered locally included that factoid).
 
GlennB said:
A car's stopping distance from 30mph is ~double the stopping distance from 20mph (Here in Wales the 'built up area' speed limit is about to be dropped from 30mph to 20mph, and a pamphlet delivered locally included that factoid).
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Yup, kinetic energy =MV^2/2.
With V = 20, V^2 = 40
With V = 30, V^2 = 90
It's not just ~double, it's 90/40 = 2.25 times the energy that has to be stopped.
 
Puppycow said:
Yeah, have you never noticed a similar phenomenon? You would only notice if you use some sort of wireless technology like BlueTooth or Wi-Fi near a microwave oven while it is running.
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I have my desktop connected to the internet through the power lines. The microwave oven reduces the speed and reliability considerably, but no other electrical appliance does. My theory is that the power lines are also affected by leaking microwave radiation.
 
I have not noticed any issue with my microwave and Wi Fi, though it is not in the path of the signal either. I tested with a phone right in front of it, and it was not disturbed. I don't know what's available these days, but Radio Shack used to sell a little microwave detector that, while hardly a scientific instrument, could detect leakage of doors and the like.

ETA, oh, I was writing a long discourse on split-phase electrical systems and how things can interfere with each other, but I just noticed you're in Denmark! Alas, I do not know how the current works there. In the US, split phase power can cause problems if two things are on the same side of the double-voltage input line, but can be improved if you switch one thing to the other side. But I don't know if that's the case in Denmark. It might, though, be worth checking if you can plug the internet signal into a different outlet, and see if there's any change.
 
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I used to get some interference on the speakers on my TV (probably an early flat screen) which I have on the kitchen table. I finally figured out it was something from the phone that was doing it - either wi-fi or Bluetooth. But I haven't seen that problem for several years.

I often forget that there was some warning of having a pacemaker and using a microwave. I haven't noticed any ill effects in my normal use. I do remember being cautioned about using a chainsaw (or anything that produces a magnetic field.)
 
Leaky microwave ovens would interfere with 2.4GHz wifi but shouldn't affect 5GHz wifi. Most hubs and devices these days can use both and don't bother the user with such details as telling you which one is in use.

I've just once noticed a file download stutter when the microwave was started. That was on an old laptop which only used 2.4GHz wifi and I was sitting directly upstairs from the microwave, like 8 or 9 feet away.
 
bruto said:
ETA, oh, I was writing a long discourse on split-phase electrical systems and how things can interfere with each other, but I just noticed you're in Denmark! Alas, I do not know how the current works there. In the US, split phase power can cause problems if two things are on the same side of the double-voltage input line, but can be improved if you switch one thing to the other side. But I don't know if that's the case in Denmark. It might, though, be worth checking if you can plug the internet signal into a different outlet, and see if there's any change.
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I am not well-versed in these matters, but multi-story house has three phases, of which one is used in each flat for 230 volt when combined with neutral, and for those appliances that need 400 volt, two phases are combined with each other. Is this what you are referring to as “split phase”?
 
steenkh said:
I am not well-versed in these matters, but multi-story house has three phases, of which one is used in each flat for 230 volt when combined with neutral, and for those appliances that need 400 volt, two phases are combined with each other. Is this what you are referring to as “split phase”?
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Sort of, except that in our system the initial feed is single phase high voltage, which is sent through a center-tapped transformer to produce a single phase 240 volt output between the two hot terminals but half that between either hot terminal and the grounded center tap. It behaves sort of like two phases, but it's not, because the split halves of the 240 volts are 180 degrees apart, while two phase would be 90 degrees apart.

Three phase distribution is not universal here, though there are three phase lines here and there. In our town, for example, there is a three phase line at one end of the town, serving a sawmill and a couple of other consumers, but at my end it's all single phase. If I want three phase power, I need to convert it myself using capacitors or a rotary transformer.

Anyway, I am assuming that since the two halves of a split phase system do not share a hot line at all, there should be some isolation that won't happen if all your circuits are using what is essentially a single tap on the transformer.
 
Trebuchet said:
Microwaves operate in the same frequency range as Bluetooth. Which I learned when I went to warm the cat food and the music cut out.
https://physics.stackexchange.com/q... signals share the same,stuff you do not want.
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My parents couldn't understand why the television in the dining room would always cut out for a few minutes before the evening news started. The TV used Chromecast connected to their Wi-fi rather than the broadcast signal. They consulted me as the person who "understands wi-fi" what might be causing it.

The dining room is actually part of the kitchen diner and they sit down at the table to eat diner whilst watching the evening news. I told them the cause was likely the microwave oven which they used to cook the vegetables just before serving. They were sceptical.

One day the microwave broke and had to be replaced. The problem went away.

I think older microwaves lack some sort of shielding that newer ones have. At least that is my educated guess.
 
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Reading an interesting article on Why we didn’t get a malaria vaccine sooner, I stumbled upon this crazy tidbit:

Malaria had become a common treatment for syphilis between the 1920s and 1940s. This was because the Austrian scientist Julius Wagner-Jauregg had discovered ‘fever therapy’: that patients could be cleared of advanced syphilis if they experienced persistently high fevers, such as those caused by malaria.

Malaria fever therapy was effective because the bacteria that causes syphilis, like many others, canʼt easily survive high temperatures. So syphilis patients could be infected by malaria, and then their malaria symptoms could be treated with antimalarial drugs.
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Heteropaternalistic superfecundation
Even though the sound of it may cause some consternation
Children from two fathers share the same uterine station
Heteropaternalistic superfecundation!
 
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I was teaching medical students this week and I thought this fact might interest people here. Why do we need oxygen? Where does it go?
 
The answer of course is mitochondria, intracellular organelles that utilise oxygen to generate activated phosphate compounds that are the 'universal' cellular fuel. The interesting thing is that mitochondria are the remnants of intracellular parasites; they are bacteria that infected 'cells'. Their closest living relations are chlamydia.

Cells (apart from neurones - brain cells) can manage without oxygen and mitochondria but only at a very low level of function.

So much of us is a support system for a group of colonising bacteria. Our lungs, heart, vascular system is really only really there to deliver oxygen to an ancestral chlamydial infection. We are entirely dependant on the energy hit we get from these bacteria as a reward for giving them a safe and successful ecological niche.

Every time I hear green-fascist eco-fanatics worrying about genetic purity and manipulating genes I think 'you have no idea how we humans are dependant on incorporated bacterial and viral genes'.
 
Ryan O'Dine said:
I recently heard this on local public radio: fat cells don't multiply very much, they mostly just enlarge.
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True, as you get fatter fat cells get bigger rather than increasing in number.

Fat cells are more active than just being fat storage, they release hormones and influence the body metabolism. The effects are poorly understood. However an example is that asthma gets worse as you gain weight and gets better as you lose weight. Weight gain asthma is poorly responsive to inhaler therapy.
 
I always liked David Deutsch's description of what the typical place in the universe is like. He argues against the sort of Copernican assumption that where we are is in no way special, and instead a typical place in the cosmos.

Deutsch says we are not in a typical place. He also uses the word "scum" here in reference to a quote by Stephen Hawking that says humans are "just a chemical scum on the surface of a typical planet that’s in orbit round a typical star on the outskirts of a typical galaxy".

Here he describes the typical place in the Universe:

What is a typical place in the universe like? Let me assume that you are reading this on Earth. In your mind’s eye, travel straight upwards a few hundred kilometres. Now you are in the slightly more typical environment of space. But you are still being heated and illuminated by the sun, and half your field of view is still taken up by the solids, liquids and scums of the Earth. A typical location has none of those features. So, travel a few trillion kilometres further in the same direction. You are now so far away that the sun looks like other stars. You are at a much colder, darker and emptier place, with no scum in sight. But it is not yet typical:you are still inside the Milky Way galaxy, and most places in the universe are not in any galaxy. Continue until you are clear outside the galaxy – say, a hundred thousand light years from Earth. At this distance you could not glimpse the Earth even if you used the most powerful telescope that humans have yet built. But the Milky Way still fills much of your sky. To get to a typical place in the universe, you have to imagine yourself at least a thousand times as far out as that, deep in intergalactic space.

What is it like there? Imagine the whole of space notionally divided into cubes the size of our solar system. If you were observing from a typical one of them, the sky would be pitch black. The nearest star would be so far away that if it were to explode as a supernova, and you were staring directly at it when its light reached you, you would not see even a glimmer. That is how big and dark the universe is. And it is cold: it is at that background temperature of 2.7 kelvin, which is cold enough to freeze every known substance except helium. (Helium is believed to remain liquid right down to absolute zero, unless highly pressurized.)

And it is empty: the density of atoms out there is below one per cubic metre. That is a million times sparser than atoms in the space between the stars, and those atoms are themselves sparser than in the best vacuum that human technology has yet achieved. Almost all the atoms in intergalactic space are hydrogen or helium, so there is no chemistry. No life could have evolved there, nor any intelligence. Nothing changes there. Nothing happens. The same is true of the next cube and the next, and if you were to examine a million consecutive cubes in any direction the story would be the same.

Cold, dark and empty. That unimaginably desolate environment is typical of the universe – and is another measure of how untypical the Earth and its chemical scum are, in a straightforward physical sense.
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Deutsch, David. The Beginning of Infinity (p. 47). Penguin Publishing Group. Kindle Edition.
 
sir drinks-a-lot said:
I always liked David Deutsch's description of what the typical place in the universe is like.
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That's not the only way to look at it, though. For example, we aren't made of space, we're made of matter. And matter isn't uniformly distributed throughout space. It's highly concentrated. So the typical conditions for matter, when averaged per atom, are considerably different than the typical conditions for space, when averaged per cubic unit of volume. The average bit of matter still doesn't look like the surface of the earth, but it's a lot closer than the average bit of space.
 
I just read a social media post stating that sharks are older than Polaris, the north star. I know a bit about evolutionary timescales and stellar evolution and I'm still regoogling the numbers. Some 200 million years versus 70. I'm not sure why this has blown my mind.
 
Wudang said:
I just read a social media post stating that sharks are older than Polaris, the north star. I know a bit about evolutionary timescales and stellar evolution and I'm still regoogling the numbers. Some 200 million years versus 70. I'm not sure why this has blown my mind.
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A quick google says that might be an underestimate for the sharks. Wow.
 
Ziggurat said:
That's not the only way to look at it, though. For example, we aren't made of space, we're made of matter. And matter isn't uniformly distributed throughout space. It's highly concentrated. So the typical conditions for matter, when averaged per atom, are considerably different than the typical conditions for space, when averaged per cubic unit of volume. The average bit of matter still doesn't look like the surface of the earth, but it's a lot closer than the average bit of space.
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On the atomic level, matter is mostly space. :p
 
arthwollipot said:
On the atomic level, matter is mostly space. :p
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For human purposes, electrons occupy most of the volume of their orbits, so no, that's not correct in any generally useful way. The ways in which it is true are the fringe cases.
 
arthwollipot said:
On the atomic level, matter is mostly space. :p
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Which is why, one day, if I try hard enough, I'll totally pass through the door without opening it. The constant banging and cussing is getting on the neighbors' nerves though.
 
The Great Zaganza said:
The polish company Nevomo has successfully tested their concept for a maglev train that uses the existing train tracks.

https://rollingstockworld.com/freig...e-idea-of-railway-infrastructure-integration/

my take: neat idea, cool that it works, of no really importance
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If this works it would have a major impact on rail transport. There are major problems with maglev some of which this will solve. Like moving a train from one lane to another takes ages with a maglev. Easy with conventional lines. Cost to lay the track will be far less.
 
The Great Zaganza said:
The polish company Nevomo has successfully tested their concept for a maglev train that uses the existing train tracks.
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Sort of. They use the existing track, but they have to basically build an additional track on top of it for the maglev capability. So it can still run traditional trains on the same lines, and don't need to take land for new tracks, but there's still going to be a big infrastructure cost for the new track.

I'd like to see them testing a curve, not just a straight shot. Cool if it works at a reasonable price, but too early to tell.
 
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