An Educational Overview for Americans explains (with plenty of pictures) the basics of the International System of Units. Book Size: A4; 27 pages (31 pages including title page, et cetera). Download your copy today. Available in Portable Document Format (*.pdf). SI An Educational Overview for Americans 2014
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Page 3 preview . . . The use of two different systems was the root cause in the loss of the $125 million Mars Climate Orbiter. NASA specified metric units in the contract. NASA and other organizations worked in metric units, but one subcontractor, Lockheed Martin, provided thruster performance data to the team in pound force seconds instead of newton seconds. The spacecraft was intended to orbit Mars at about 150 kilometers altitude, but the incorrect data meant that it probably descended instead to about 57 kilometers, burning up in the thin Martian atmosphere.
Page 13 preview . . . The millimeter is a practical unit of length for many everyday measurements including level of rainfall, paper and camera film. The most common paper size is A4 (297 x 210 mm); 35 mm film is common.
Tardigrades (commonly known as waterbears or moss piglets) are small, water-dwelling, segmented animals with eight legs. They form the phylum Tardigrada, part of the superphylum Ecdysozoa. The first tardigrades were discovered by Johann August Ephraim Goeze in 1773. Since 1778, over 500 new tardigrade species have been found. Usually, Tardigrades are 1 mm when they are full grown. They are short and plump with 4 pairs of poorly articulated lobopodial limbs. Each limb has 4 to 8 claws also known as disks. Tardigrades all possess a buccopharyngeal membrane apparatus, which, along with the claws, are used to differentiate the different species. Tardigrades are covered in cuticle which contains chitin and protein.
Tardigrades were first discovered in 1773 by Johann August Ephraim Goeze, who called them kleiner Wasserbär, meaning little water bear in German. The name Tardigrada means slow walker and was given by Lazzaro Spallanzani in 1777.
The name water bear comes from the bearlike way they walk. The biggest adults may reach a body length of 1.5 mm; the smallest below 0.1 mm; freshly hatched tardigrades may be smaller than 0.05 mm.
About 1,150 species of tardigrades have been described. Tardigrades occur throughout the world from the Himalayas above 6,000 meters to deep sea below 4,000 meters and from polar regions to equator.
The most convenient place to find tardigrades is on lichens and mosses. Other environments are dunes, beaches, soil, and marine or freshwater sediments, where they may occur quite frequently (up to 25,000 animals per liter). Tardigrades often can be found by soaking a piece of moss in spring water.
Tardigrades are able to survive in extreme environments that would kill almost any other animal. Some can survive temperatures of close to absolute zero, or 0 Kelvin (-273 °C), temperatures as high as 151 °C, 1,000 times more radiation than other animals, and almost a decade without water. Since 2007, tardigrades have also returned alive from studies in which they have been exposed to the vacuum of space for a few days in low Earth orbit. Tardigrades are the first known animal to survive in space.