Wikipedia:Reference desk/Archives/Science/2019 December 23

= December 23 =

Artifact on old TV - dark area around a bright area
In the screenshot from TV at Mercury-Atlas_6, there is a dark area around the bright flames. This is very common in TV of the area. What caused this artifact? Something about the TV camera? Videotape? Kinescope? Bubba73 You talkin' to me? 03:43, 23 December 2019 (UTC)
 * I think you mean in this image, . But I don't know the answer to the question. Bus stop (talk) 03:48, 23 December 2019 (UTC)
 * Yes, the one from TV. Bubba73 You talkin' to me? 04:59, 23 December 2019 (UTC)
 * It looks a bit like lens flare to my eye. You may find some answers at the TV Tropes and Lens flare articles. MarnetteD&#124;Talk 03:58, 23 December 2019 (UTC)


 * I don't think it is lens flare - lens flare doesn't look like that. I've seen it in a lot of old TV surrounding a bright area.  Bubba73 You talkin' to me? 04:59, 23 December 2019 (UTC)

You can see this effect in other places too, for instance this infrared video. The video system can be adjusted so that hot objects are white, or flipped to the negative, as in this screenshot. Bubba73 You talkin' to me? 05:34, 23 December 2019 (UTC)
 * The black halo is not lens flare but a feature of the image orthicon Video camera tube which tends to flare in bright light, causing a dark halo to be seen around the bright object; this anomaly was referred to as blooming in the broadcast industry when image orthicon tubes were in operation. DroneB (talk) 15:05, 23 December 2019 (UTC)


 * Thanks, and that is discussed here: Video_camera_tube. Bubba73 You talkin' to me? 17:53, 23 December 2019 (UTC)

Running Rail Trains on Roads
Could it be possible to replace train wheels with tires and drive on roads? — Preceding unsigned comment added by 91.159.43.14 (talk) 13:39, 23 December 2019 (UTC)
 * [OP, I have added a heading to your question to set it off from the previous one. In future, please create a new query by clicking the 'New Section' tab at the top of the page and filling in a suitable 'Subject/Headline'.]
 * To answer your question: No, this would generally not be possible.
 * Firstly, train vehicles designed to run on steel rails are usually much heavier than road vehicles, and their weight typically exerts a pressure of several tons per (solid steel) wheel (see Adhesion railway and Axle load); such pressures would be unsustainable for a pneumatic-tyred wheel of similar dimensions, and would also damage the road. Steel wheels without rubber tyres would simply sink into the road immediately.
 * Secondly, rail-trains work because the rolling friction of steel wheels on steel rails is very low, enabling a comparatively weak motive force to move the train. The rolling resistence of rubber-tyred road vehicles is much higher, requiring a combination of lighter vehicle weight and a more powerful engine relative to that weight. On a road, with rubber wheels, a train designed for rails would be able to propel itself barely if at all.
 * Thirdly, rail vehicles are not steered, since they are guided by the rails. Such vehicles would have to be modified extensively with steering mechanisms.
 * Fourthly, such a converted rail train would cause huge inconvenience to other road users in most circumstances, although in some isolated circumstances road trains are a thing.
 * Of course tramways, where a light rail train runs on tracks alongside or set into a road, are commonplace, but they cannot, of course, deviate from the fixed rails. Also, passenger road vehicles have sometimes been adapted to run on rails (usually on narrow-gauge railways – see the Galloping Goose (railcar)), so it would be possible to design a dual use vehicle and even to couple two or more together thus forming a train, but there not many contexts in which this would be both feasible and more economical than the currently used solutions. {The poster formerly known as 87.81.230.195} 90.199.211.222 (talk) 14:47, 23 December 2019 (UTC)
 * Good answer; I think it hits all the important points. It should however be noted that there are trains that run on rubber tires, such on the Paris Metro Line 6 and the Montreal Métro. However, they don't run on conventional roads.  There are special concrete rails that provide the necessary support, and additional wheels running sideways along additional rails to steer the train, as you can see here. --142.112.159.101 (talk) 21:10, 23 December 2019 (UTC)


 * Also see this article about a new Chinese system where trams are guided by lines painted on the road. The driver can override the steering if necessary to avoid obstructions.  Rojomoke (talk) 23:33, 23 December 2019 (UTC)


 * This is done regularly, for railway service vehicles such as diggers. It turns out to be simplest for them to have two sets of wheels, a set of railway wheels lifted hydraulically or lowered to run on rails. The drive is done through the road wheels. They usually have either cylindrical tyres, or an inner double tyre, to run on the rail surface and drive them. Andy Dingley (talk) 23:40, 23 December 2019 (UTC)


 * Editor 90.199.211.222 mentioned it briefly above, but this Australian feels that the best match for the title of the question has to be a Road train. Quite common when you get away from the big cities in this country. Road_train_(25).jpg HiLo48 (talk) 00:03, 24 December 2019 (UTC)


 * A steam tractor, common from the late 19th to early 20th century, might be the sort of thing the OP envisioned. It has steel tires, a firebox and boiler, an steering. It can drive on roads or fields. Edison (talk) 19:04, 24 December 2019 (UTC)


 * It's maybe worth linking to Road–rail vehicle. While some of the stuff there has already been mentioned by Andy Dingley and other, it does mention how attempts to use this for purposes other than maintenance and the like have not been particularly successful. It also mention how these are always road vehicles or something similar to road vehicles, converted to also work on rail. It doesn't really cover the Dual-mode transit or Dual-mode vehicle stuff although our coverage of that seems poor anyway. (Likewise Rubber-tyred tram.) BTW, Guided bus more examples of what Rojomoke mentioned and other related stuff. Nil Einne (talk) 10:10, 25 December 2019 (UTC)

Shoots faster than his own shadow
Lucky Luke is called "the man who shoots faster than his own shadow". Doesn't everyone? When someone moves their arm to shoot a gun, the light travelling from where their arm used to be is still travelling towards the ground, and the shadow still has the old position. The time difference is just so minuscule that this isn't noticed. Is this correct? J I P &#124; Talk 15:10, 23 December 2019 (UTC)
 * Light travels around 186,000 miles per second, so figure out how long it would take light to cover 6 feet or so. Then if you had a film or video camera that could shoot millions of frames per second, you might able to detect it. Otherwise, that's just a joke. Kind of like when Cool Papa Bell was said to be so fast that when he flipped the light switch off, he could be in bed before the room got dark. ←Baseball Bugs What's up, Doc? carrots→ 17:22, 23 December 2019 (UTC)
 * Light travels 6 feet in 6.1 nS, in which time a bullet moves only about 2 µm. DroneB (talk) 17:45, 23 December 2019 (UTC)
 * Yes, JIP, your assumption is correct. One's shadow is fractionally behind the actions one takes, by the equivalent to the speed of light.  You are faster than your shadow by the amount of time it take the light hitting your moving arm and the light next to your arm, (its future position) takes to hit the place where the shadow will be cast.  Anton 81.131.40.58 (talk) 09:11, 24 December 2019 (UTC)
 * Assume an observer is located at a distance of 1 light minute from Lucky Luke´s position.
 * LL draws his gun at 12:00 precisely and shoots at the observer.
 * This being a comic strip, LL´s bullet travels at the speed of c.
 * To the observer, LL stands motionless until the time 12:01.
 * Unluckily, at precisely this time, the observer will be killed by a bullet.
 * QED. --Cookatoo.ergo.ZooM (talk) 14:43, 24 December 2019 (UTC)


 * PS: There is no difference between a bullet and a shadow-producing photon (both traveling at c) in this minute whodunnit.  --Cookatoo.ergo.ZooM (talk) 15:10, 24 December 2019 (UTC)
 * Sanity checks: "Assume an observer is located at a distance of 1 light minute from Lucky Luke´s position." - One light-minute is almost 1.8 x 1010 meters or over 11 million miles.
 * "...LL´s bullet travels at the speed of c " - The special theory of relativity implies that only particles with zero rest mass may travel at the speed of light.
 * A rifle bullet without air resistance could travel the distance in 7 months. DroneB (talk) 17:54, 30 December 2019 (UTC)