Wikipedia:Reference desk/Archives/Science/2024 June 17

= June 17 =

Unit usage
--40bus (talk) 21:01, 17 June 2024 (UTC)
 * 1) Is the height of clouds and flying animals from earth's surface measured in meters or feet in most countries? I have seen using feet as primary units in this wiki's articles.
 * 2) Are distances on association football pitch, such as length of goal kick, measured in meters in most continental European countries?
 * 3) Are rink and equipment sizes in ice hockey measured in metric units in most continental European countries?
 * 4) Is there any country that measures American football field sizes in metric units?


 * In aviation, height is often measured in feet, even in countries that otherwise make little use of Imperial or US customary units. This would apply to clouds, but flying animals don't come up too much in aviation, unless your name is Sully Sullenberger. Jc3s5h (talk) 21:07, 17 June 2024 (UTC)
 * In aviation, altitude is usually measured in flight levels, with one flight level corresponding to the barometric pressure difference of 100 feet under normal conditions. Using barometric altitude is due to the fact that it is easier to measure well, and good enough to ensure vertical separation of aircraft. That on FL corresponds to 100ft is a historical relic, but air traffic is extremely conservative. --Stephan Schulz (talk) 21:19, 17 June 2024 (UTC)
 * Regarding this, is there any English-speaking country that has metric flight levels? --40bus (talk) 21:34, 17 June 2024 (UTC)
 * According to the FAA's Aeronautical Information Manual (page 231 of the PDF) in the US feet are used up to but not including 18,000 feet MSL (that is, above mean sea level). At and above 18,000 MSL flight level is used. Moving on to page 601 of the PDF, there is a complex discussion of setting the aircraft's altimeter, but essentially instructs to use the current actual barometric pressure if below 18,000 feet MSL. But at or above 18,000 feet MSL all operators will set 29.92 inches of mercury, which is considered the standard setting. The manual doesn't say so, but I've been taught that below 18,000 feet the chief concern is colliding with terrain, and above that the chief concern is colliding with other aircraft. The altimeter setting is chosen to minimize the risk in the respective altitude ranges.
 * Other countries may have a transition altitude other than 18,000 MSL. Jc3s5h (talk) 21:53, 17 June 2024 (UTC)
 * Not sure about English-speaking country. But Chinese ATC controllers frequently issue metric flight levels.in their control, to the point where pilots have a conversion chart from metric to imperial (e.g FL177 generally translates to 6000m) Hanoi2020 (talk) 17:24, 30 June 2024 (UTC)
 * Outside the US, American football is virtually nonexistent, and supporters are likely to be Americans. NFL Europe says that the league gave an additional point for field goals of 50 yards, not 45 metres.  Nyttend (talk) 08:03, 18 June 2024 (UTC)
 * User:40bus, when you say American football field sizes, do you mean measuring American football fields specifically, or anything roughly that size? Rugby league and rugby union, which are related to American football, are played on fields a bit larger than American football, and their dimensions are measured in metres.  Nyttend (talk) 19:39, 18 June 2024 (UTC)


 * Heights of clouds, birds, buildings, anything are measured in metric in most of the world. The only exception is aviation, which shifted in most of the world post-World War 2 from metric to British/American units. It had something to do with the post-war dominance of the British and American aviation industry. Historical aircraft (pre-1945), but also many modern gliders, from Europe typically have altimeters in metres and airspeed indicators in km/h. PiusImpavidus (talk) 10:48, 18 June 2024 (UTC)
 * Meteorology tends to use the same units as aviation (or at least they did when I worked in the field, over 20 years ago), resulting in a weird mess of systems. So heights and altitudes in feet (unless we were dealing with things more than about 15-20km up, when we switched to km).  Visibility in metres, but long distances in nautical miles.  Speed in knots.  Temperature in Celsius.  Pressure in millibars / hectopascals. Iapetus (talk) 14:45, 18 June 2024 (UTC)
 * Of course, the nautical mile is a very different matter from anything else non-metric, since it's based on the distance of a minute of latitude, because such a figure is very easy to measure on maps. The nautical mile article notes that it was sanctioned for use by France and that other metric countries have defined it in metric terms (and makes an uncited claim that many metric countries approved its use), which is rare or unique for pre-metric units.  Nyttend (talk) 19:39, 18 June 2024 (UTC)
 * I have seen using feet as primary units in this wiki's articles.
 * We have unit conversion templates that should make it possible to see the units of your choice in any given article. They haven't yet been applied consistently to all articles, but you can update them yourself if you encounter places where they're missing. -- Avocado (talk) 22:26, 19 June 2024 (UTC)

Football
I found that in articles of major association football matches use yards first in distances and lengths of shots, even macthes played in completely metric countries. Should they use meters first? --40bus (talk) 13:47, 19 June 2024 (UTC)
 * How do the news media cover it? ←Baseball Bugs What's up, Doc? carrots→ 17:44, 19 June 2024 (UTC)
 * I meant that this wiki's articles do that. --40bus (talk) 18:41, 19 June 2024 (UTC)
 * Do Wikipedia's articles conform to the way the news media cover it? ←Baseball Bugs What's up, Doc? carrots→ 18:56, 19 June 2024 (UTC)
 * I think it comes down to how it was cited in primary/secondary sources. If CBS Sports says someone had a 50yd TD then the people writing and quoting would likely follow the same procedure. Hanoi2020 (talk) 17:26, 30 June 2024 (UTC)

Extracting energy from the Earth's rotation
I've been thinking about the Focault pendulum, and that gave me an idea. For simplicity, assume I put a gyro on a freely rotating platform, exactly at the North Pole, with the axis of the gyro parallel to the ground (and hence the equatorial plane). As I understand it, the gyro-mount would rotate once every 24h relative to the Earth - the gyro remains stable, the Earth is rotating under it. What would now happen we connect a generator to the platform (possibly via a gearbox to get a bit above 1rpd). Would it be possible to extract useful amounts of energy from this construct? I actually have no idea how to calculate this... --Stephan Schulz (talk) 21:11, 17 June 2024 (UTC)
 * If you wish to extract energy from the Earth's rotation, there are simpler ways to do it. AndyTheGrump (talk) 21:16, 17 June 2024 (UTC)
 * Tidal power draws mainly on the energy of the Moon's orbit. A windmill blown by a hurricane is an example of drawing power via Coriolis effect from the Earth's rotation. Philvoids (talk) 21:25, 18 June 2024 (UTC)
 * Yes, but those are boring. I want the mad scientist solution. --Stephan Schulz (talk) 21:20, 17 June 2024 (UTC)
 * I'm not sure, but aren't the present day Focault Pendulum systems powered using an electromagnet so that they keep going indefinetely? Getting energy from this would never be more than the energy inserted in it using the magnet. Rmvandijk (talk) 08:37, 18 June 2024 (UTC)


 * The lazy answer is: thermodynamics says no. Without transporting angular momentum from the Earth to anywhere off Earth, the only energy that can be extracted is the rotational energy of the flywheel and you won't get more than what you used to spin up your gyroscope.
 * Now it's clearly possible to extract energy from the gyro-mount in the way you described. The gearbox will apply a torque to the gyro-mount, trying to put the gyro's spin axis vertical, but it's restricted in its movement, so there will be another torque perpendicular to both the gyro's spin axis and the vertical, causing the gyroscope to precess with the Earth's rotation. But it's possible to tune this torque such that the gyro's precession rate will be half a revolution per day, so that neither the torque nor the angular speed of the mount relative to Earth will be zero, so that power can be extracted. It's not immediately obvious how this energy can be extracted from the rotational energy of the spinning gyroscope, as that requires a torque along the gyro's spin axis. I suspect it has something to do with precession of the Earth itself. PiusImpavidus (talk) 11:53, 18 June 2024 (UTC)
 * Certainly, the gyro's spin axis is mechanically restricted to a flat plane, then the gyro and the Earth are torquing the gearbox and doing work in that plane. Operating it at low speed on a magnetic suspension reduces windage and friction. Hmmm, of course, for it to be an effective energy source the rate of work extracted from their rotations must be greater than the rate of energy needed in maintaining its operation. Yet whenever I stand up or lay back down, the Earth's rotational energy and momentum are redistributed between my body and the Earth. Thus I don't see how or why energy and momentum conservation is an issue with this clever invention. Modocc (talk) 23:27, 18 June 2024 (UTC)
 * In other words, the angular momentum and mass-energy of the entire Earth is conserved, but the energized gyro(s), the rotating platform and its gearboxes are redistributing it, hence the Earth is both the source and repository of the energy. Moreover, this idea is related to the Coriolis effect which is very small, yet it would be simple enough to demonstrate its principles on a much smaller scale: simply substitute a spinning wheel for the planet. A second free-spinning wheel placed on the axle serving as the platform per the OP's specs, should act as a regenerative brake. Modocc (talk) 22:11, 19 June 2024 (UTC)