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DVD Smith
1269619.  Fri Jan 05, 2018 4:29 pm Reply with quote

Quickest ever
In 1957, the record for the fastest man-made object ever recorded was broken…by a giant nuclear-powered manhole cover. [1][2][3]

The manhole cover in question was a 4ft-wide round metal plate, and was covering the top of an underground nuclear test chamber in Los Alamos, New Mexico, where the US government had recently started conducting nuclear tests underground to reduce the chance of fallout. They placed a 1-kiloton device at the bottom of the 500ft-deep cylindrical chamber, and detonated it, with a high-speed camera trained on the round metal plate covering the hole. When the device detonated, it basically turned the chamber into an enormous gun, which blasted the cover from the hole so quickly that the high-speed camera (reported to have a shutter speed of 160 frames/second [4]) only caught it on film for one frame. The scientist in charge, Dr Robert Brownlee, recorded that, from the speed of the camera and the distance visible in the photo, he calculated the speed of the plate to be “six times the escape velocity of the Earth”, which would put it in the region of 66 km/s, or 150,000 mph. [5] [6] Thermodynamic calculations performed on this website would appear to support this, as with a few assumptions they calculated a launch velocity of 56 km/s, or 125,000 mph, approximately five times the Earth’s escape velocity.

Since the incident occurred, the story has been reported over the years as “the first man-made object sent into space” due to the manhole cover’s speed, the nuclear test taking place a few months before Sputnik launched, and the fact that the plate was never found. [2][7] Brownlee disputes this, as he believes the plate would have burned up in the atmosphere, like an upwards-travelling meteor. [5] [8]

Since the space age began, more than one spacecraft has claimed to be the fastest. In summer of 2016, the NASA spacecraft Juno arrived at Jupiter, with several websites calling it “the fastest spacecraft ever”, with Jupiter’s gravity accelerating it to a calculated top speed of 165,000 mph, or 74 km/s. [9][10] However, it’s hard to compare, since all space-travel speed calculations are done using a frame of reference, usually a large gravitational body. [11] The solar probe Helios 2 officially holds the record, as measured relative to the Sun it achieved a speed of 147,000 mph, but when measured relative to the Earth (as Juno was) it reached a whopping 215,000 mph, or 96.2 km/s. The record is set to be undisputedly broken again when the Solar Probe Plus launches in July 2018, which is calculated to reach Sun-relative speeds of 450,000 mph, or 200km/s. [12]

Quicksand
It’s a classic trope of lots of films, TV shows and video games – pits of wet liquid-y sand that suck people in and swallow them whole. It became such a common Hollywood plot device that at its peak in the 1960s, one in every 40 films released featured quicksand in it at some point. [13] Quicksand is defined as sand (or mud or clay) that is saturated with water, to the point where the friction between the sand particles is removed and so the sand cannot support the mass of a human in the same way dry sand can. (It becomes a non-Newtonian fluid, just like custard.) [14]

In reality, the chances of quicksand “swallowing you whole”, as it were, are practically impossible. This isn’t to say it isn’t dangerous, as it can still kill you if you get stuck, but experiments have shown that you’re not gonna sink below the surface like all the films tell you; depending on the viscosity of the quicksand, you’ll either bob on the surface from the buoyancy or you’ll sink halfway and no further. [15][16][17][18]

However, so-called “dry quicksand” can absolutely swallow you whole. Dry quicksand is like regular sand, but with enough pockets of air between the sand particles that friction is removed in the same way that water saturation does. Because dry quicksand doesn’t have any water, it doesn’t have the same buoyancy effect, and so you just sink and sink. [19][20] In addition, every time you exhale, the volume of your chest reduces and the sand quickly moves to fill that space, increasing the pressure on your chest and making it much harder for you to breathe in. The existence of dry quicksand in nature is disputed, but its effects are just as visible and just as deadly in other materials – in 2002 a man in Germany was rescued from a grain silo after he fell in and started sinking into the grain, which started completely swallowing him. [14][21]

The most likely cause of death from getting stuck in quicksand is death from exposure or starvation, or drowning when the tide comes in (since most quicksand is located near water). [Klaxon: Suffocating/drowning due to sinking into the sand.] However, deaths by quicksand are still relatively rare – in 2016 the Houston Chronicle reported only one death in Texas due to quicksand in the previous five years. [22] The best advice if you get stuck is not to struggle, and try to float on the surface to spread your mass out as much as possible, and hopefully your legs will pop free. [16] If you tried to lift your legs out vertically while standing upright, you’d need to exert a force of 100,000 newtons – the equivalent of the strength needed to lift a medium-sized car. [15]

 

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