Warplanes

Airplanes were first used in warfare during World War I (1914-1918). They have been vital elements of armed combat ever since. Warplanes range from fast, nimble, jet-powered fighters to battlefield helicopters and tankers for in-flight refueling. Between them, they find and destroy enemy aircraft and targets on the ground. Warplanes also help transport troops and equipment to and from the battlefield. In peacetime, military transport aircraft often help with emergencies and famine itself.

Warplanes are either combat aircraft or non-combat aircraft, which support other military forces. Combat aircraft includes fighters (also called interceptors), which win superiority in the air, enabling other aircraft to operate over a battlezone, bombers, and fighter-bombers. Non-combat aircraft carry out reconnaissance, or carry troops and equipment rapidly to a battle zone.

Universe

Everything that exists makes up the Universe, from the smallest particles to the biggest structures, whether on Earth or space. It includes everything that is visible, invisible, everything that is known and more that is unknown. Over time, humans have had different ideas of what the Universe is and how it works, how it started and what its future is. Today, scientists know more than ever before, but there is much still to be learnt.

The common object in the Universe is the star. There are billions and billions of them. At least one of these, the sun, has planets. One of these planets, Earth, has life. On the face of it stars, planets and humans are very different, but they do have things in common. They are all made of the same chemical elements or compounds of them and they are all affected by the laws of science such as gravity and the electromagnetic force. By studying the constituents of the Universe and understanding the laws, scientists can build up a picture of the Universe and discover its past and predict its future.

Solids

The phrase “Solid as a rock” makes us think of something that is very hard and rigid. But rock is only one example of a solid and some solids are weaker or more flexible than others. A solid is any piece of matter that has a definite shape and volume and does not flow like a liquid or gas. When solid gets hot it may turn into liquid the heat of a volcano can turn even the hardest rock into liquid lava.

Inside solid, tiny particles of matter called atoms or molecules are packed together in orderly patterns, like bricks in a wall. The particles are “cemented” firmly in place by forces called chemical bonds. Although solid particles are held close to their neighbors and cannot move away, they vibrate around fixed positions.

Socrates

The great thinker Socrates, who lived 2,400 years ago, was one of the most important people in the history of science and philosophy. He wrote no books, and we know litter about the events of his life, but Socrates still has a strong influence on the western thoughts. He believed strongly that the philosophy should concern itself with the conduct of everyday life, not with abstract ideas. He valued human intelligence, reason and open discussion, and, through his teachings, showed people how to live a good and virtuous life.

In his middle age, Socrates studied the teachings of other great thinkers and developed a philosophy of his own and debated regularly with other philosophers. Most of what we know about his philosophy comes from the writings of two of his pupils, the philosopher Plat and the historian Xenophon.

Marie Curie

The physicist Marie Curie was a pioneer in the science of radioactivity- the study of powerful rays emitted by certain rare materials. Her work changed Physics and Chemistry and formed a basis for later research in nuclear physics. She discovered two previously unknown elements and also founded an important research institute. In 1903, she shared the Nobel Prize for physics with her husband Pierre, with whom she worked, and French scientist Henri Becquerel. In 1911, she was awarded Nobel Prize for chemistry.

For much of her life, Marie Curie worked under difficult conditions. Her laboratory was in an unheated shed and much equipment was home made. Pierre helped her design and builds some of her equipment, including a device called an electrometer, which measured the strength of radiation coming from Uranium compound.

She died in 1934 after suffering for years due to the illness caused by the exposure to radiations. 

Gravity

Without gravity, we would fly off the spinning earth and into the space. Gravity is a force of attraction that acts between any two objects. The objects can be as large as galaxies or as small as sub atomic particles. The strength of the gravity between two objects depends on their masses and the distance between their centers. Objects with large masses exert a strong force of gravity. Objects far apart attract each other weakly.

Gravity always acts towards the centre of Earth, defining the downwards direction every point on the planet surface. Gravity pulls the juggling ball towards the ground, slowing it as it rises, and speeding it up as it falls. The ball also pulls on the Earth but the earth is so massive that the ball’s gravity has no noticeable effect.

Exploration

Since the earliest times, people have been curious about the world in which they live. For more than 3,000 years, explorers have charted most of Earth’s surface by land and sea. Often these brave pioneers went out into the unknown inspired by more than mere curiosity. Sometimes they went in search of riches, or to find new and less overcrowded places to live, or in a quest for scientific knowledge. In the course of mapping the world, explorers quashed many myths while bringing back true stories that could seem even stranger than fiction.

In ancient times, people such as the Phoenicians explored new regions in their quest for trading partners. The Greeks and Romans also discovered more about the world as their empires expanded. People began to read about far-flung places in books by classical geographers such as Strabo.