| There are | many species of insects. | ²ñíóº áàãàòî âèä³â êîìàõ. | |
| many species of insects | in rain forests. |  òðîï³êàõ áàãàòî âèä³â êîìàõ. |
². Decide which of these statements are true and which are false.
1. Bearings help to prevent wearing of parts caused by friction. 2. The concept of bearing is rolling instead of jumping. 3. Magnetic bearings are used in fly-wheels. 4. Ancient Egyptians put big stones under logs when they constructed pyramids. 5. Giant ball bearings are used in San Francisco’s Opera House to prevent the building from ruining in earthquakes.
²². Answer the following questions.
1. Why things that slide begin to slow down? 2. At what speed do some flywheels run? 3. Why do magnetic bearing withstand such speeds? 4. How many columns support the building of San Francisco airport? 5. What force moves the columns back to their places after an earthquake?
Text 10. The Properties of Diamonds
Active Vocabulary:
| rough | ãðóáèé | solid | òâåðäå ò³ëî |
| to process | îáðîáëÿòè | orthoclase | îðòîêëàñ (ì³íåðàë) |
| gem | êîøòîâíèé êàì³íü | file | íàïèëîê |
| to purchase | êóïóâàòè | to link | ç’ºäíóâàòè |
| hard | òâåðäèé | lattice | ðåø³òêà |
| to rank | çàéìàòè ì³ñöå | to share | ä³ëèòèñÿ |
Diamonds are found as rough stones and must be processed to create a sparkling gem that is ready for purchase.
Diamonds are the crystallized form of carbon created under extreme heat and pressure. It’s this same process that makes diamonds the hardest mineral we know of. A diamond ranks a 10 on the Mohs Hardness Scale. The Mohs Scale is used to determine the hardness of solids, especially minerals. It is named after the German mineralogist Friedrich Mohs. Here’s the scale, from softest to hardest:
talc – easily scratched by the fingernail;
gypsum – just scratched by the fingernail;
calcite – scratches and is scratched by a copper coin;
fluorite – not scratched by a copper coin and does not scratch glass;
apatite – just scratches glass and is easily scratched by a knife;
orthoclase – easily scratches glass and is just scratched by a file;
quartz – (amethyst, citrine, tiger’s-eye, aventurine) not scratched by a file;
topaz – scratched only by corundum and diamond;
corundum – (sapphires and rubies) scratched only by a diamond;
diamond – scratched only by another diamond.
Even though diamond is only one level higher on the scale than corundum, diamond can be anywhere from 10 to hundreds of times harder than this class of gems.
It is the molecular structure of diamonds that makes them so hard. Diamonds are made of carbon atoms linked together in a lattice structure. Each carbon atom shares electrons with four other carbon atoms, forming a tetrahedral unit. This tetrahedral bonding of five carbon atoms forms an incredibly strong molecule. Graphite, another form of carbon, isn’t as strong as diamond because the carbon atoms in graphite link together in rings, where each atom is only linked to one other atom.