Archimedes (c.287-212Bc) was one of the first great scientists. He created the sciences of mechanics and hydrostatics.
Archimedes was a Greek who lived in the city of Syracuse, Sicily. His relative, Hieron II, was king of Syracuse.
Archimedes’ screw is a simple pump supposedly invented by Archimedes. It scoops up water with a spiral device that turns inside a tube. It is still used in the Middle East.
To help defend Syracuse against Roman attackers in 215Bc, Archimedes invented many war machines. They included an awesome ‘claw’ — a giant grappling crane that could lift whole galleys from the water and sink them.
Archimedes was killed by Roman soldiers when collaborators let the Romans into Syracuse in 212Bc.
Archimedes analysed levers mathematically. He showed that the load you can move with a particular effort is in exact proportion to its distance from the fulcrum.
Archimedes discovered that objects float because they are thrust upwards by the water.
Archimedes’ principle shows that the upthrust on a floating object is equal to the weight of the water that the object pushes out of the way.
Archimedes realized he could work out the density, or specific gravity, of an object by comparing the object’s weight to the weight of water it pushes out of a jar when completely submerged.
Archimedes used specific gravity to prove a sly goldsmith had not made King Hieron’s crown of pure gold.
More than 70% of all bird species – over 5,000 species altogether – are perching birds, or Passerines. They have feet with three toes pointing forwards and one backwards, to help them cling to a perch.
Perching birds sing – this means that their call is not a single sound, but a sequence of musical notes.
Songbirds, such as thrushes, warblers and nightingales, are perching birds with especially attractive songs.
Usually only male songbirds sing – and mainly in the mating season, to warn off rivals and attract females.
Sparrows are small perching birds found in many parts of the world. Sparrows are seed-eaters with the house sparrow specializing in grain. Changes in farming practices are thought to account for this bird’s dramatic decline in numbers in Britain.
Starlings often gather on overhead cables ready to migrate.
Sparrows are small, plump birds, whose chirruping song is familiar almost everywhere.
Starlings are very common perching birds which often gather in huge flocks, either to feed or to roost.
All the millions of European starlings in North America are descended from 100 set free in New York’s Central Park in the 1890s.
Many perching birds, including mynahs, are talented mimics. The lyre bird of southeastern Australia can imitate car sirens and chainsaws, as well as other birds.
The red-billed quelea of Africa is the world’s most abundant bird. There are over 1.5 billion of them.
Galileo Galilei (1564-1642) was a great Italian mathematician and astronomer.
Galileo was born in Pisa on 15 February 1564, in the same year as William Shakespeare.
The pendulum clock was invented by Galileo after watching a swinging lamp in Pisa Cathedral in 1583.
Galileo’s experiments with balls rolling down slopes laid the basis for our understanding of how gravity affects acceleration (speeding up).
Learning of the telescope’s invention, Galileo made his own to look at the Moon, Venus and Jupiter.
Galileo described his observations of space in a book called The Starry Messenger, published in 1613.
Through his telescope Galileo saw that Jupiter has four moons (see Jupiter’s Galilean moons). He also saw that Venus has phases (as our Moon does).
Jupiter’s moon and Venus’s phases were the first visible evidence of Copernicus’ theory that the Earth moves round the Sun. Galileo also believed this.
Galileo was declared a heretic in 1616 by the Catholic Church, for his support of Copernican theory. Later, threatened with torture, Galileo was forced to deny that the Earth orbits the Sun. Legend has it he muttered `eppur si muove’ (`yet it does move’) afterwards
Life on Earth depends on the layer of ozone gas in the air (see atmosphere), which shields the Earth from the Sun’s ultraviolet (UV) rays. Ozone molecules are made from three atoms of oxygen, not two like oxygen.
In 1982 scientists in Antarctica noticed a 50 percent loss of ozone over the Antarctic every spring. This finding was confirmed in 1985 by the Nimbus-7 satellite.
The ozone hole is a patch where the ozone layer becomes very thin.
The ozone hole appears over Antarctica every spring.
The ozone hole is monitored all the time by the TOMS (Total Ozone Mapping Spectrometer) satellite.
The loss of ozone is caused by manufactured gases, notably chlorofluorocarbons (CFCs), which drift up through the air and combine with the ozone.
CFCs are used in many things, from refrigerators and aerosol sprays to forming the foam for fast-food cartons.
CFCs were banned in 1996, but it may be at least 100 years before the ban takes effect. The hole is still growing.
UV rays from the Sun come in three kinds: UVA, UVB and UVC. Both oxygen and ozone soak up UVA and UVC rays, but only ozone absorbs UVB. For every
Meteorologists predict the world temperature will rise between 2 and 4°C by 2030 unless we 1 percent loss of ozone, 1 percent more UVB rays reach the Earth’s surface.
Most of the world’s great lakes lie in regions that were once glaciated. The glaciers carved out deep hollows in the rock in which water collected. The Great Lakes of the USA and Canada are partly glacial in origin.
In Minnesota, USA 11,000 lakes were formed by glaciers.
The world’s deepest lakes are often formed by faults in the Earth’s crust, such as Lake Baikal in Siberia (see Asia) and Lake Tanganyika in East Africa.
Many of the world’s great lakes were formed by glaciations, and will eventually disappear.
Most lakes last only a few thousand years before they are filled in by silt or drained by changes in the landscape.
The world’s oldest great lake is Lake Baikal in Siberia, which is over 2 million years old.
The Great Lakes include three of the world’s five largest lakes: Superior, Huron and Michigan.
The world’s largest lake is the Caspian Sea (see Asia), which is a huge saltwater lake below sea level. It covers 371,000 sq km.
The world’s highest great lake is Lake Titicaca in South America, which is 3812 m above sea level.
The world’s lowest great lake is the Dead Sea between Israel and Jordan. It is 399 m below sea level and getting lower all the time.
The largest underground lake in the world is Drauchen-hauchloch, which is inside a cave in Namibia.