Enb5 Ew - Black Holes Writing Exercise

A2 English Language Editorial Writing Practice – Black Holes •

The following four extracts give information about black holes. Information about the origin of the texts is given at the end of the activity. Write a 300-word introduction to a programme about ‘black holes’ suitable for a radio programme to be relayed during Radio 4’s Children’s Science Hour. Try to consider the conventions of a radio programme – the use of silences, music, sounds and so on.

Extract A:

Introduction to Black Holes: What is a Black Hole?

A black hole is a region of space-time from which nothing can escape, even light. To see why this happens, imagine throwing a tennis ball in the air. The harder you throw the tennis ball, the faster it is travelling when it leaves your hand and the higher the ball will go before turning back. If you throw it hard enough it will never return, the gravitational attraction will not be able to pull it back down. The velocity the ball must have to escape is known as the escape velocity and for the earth is about 7 miles a second. As a body is crushed into a smaller and smaller volume, the gravitational attraction increases, and hence the escape velocity gets bigger. Things have to be thrown harder and harder to escape. Eventually a point is reached when even light, which travels at 186 thousand miles a second, is not travelling fast enough to escape. At this point, nothing can get out as nothing can travel faster than light. This is a black hole. Extract B Black hole, an extremely dense celestial body that has been theorised to exist in the universe. The gravitational field of a black hole is so strong that, if the body is large enough, nothing, including electromagnetic radiation, can escape from its vicinity. The body is surrounded by a spherical boundary, called a horizon, through which light can enter but not escape, it therefore appears totally black. Extract C

Black Holes

Of all the odd creatures in the celestial zoo, the ‘black hole’ is the oddest. To understand it, concentrate on gravity. Every piece of matter produces a gravitational field. The larger the piece, the larger the field. What’s more, the field grows more intense the closer you move toward its centre. If a large object is squeezed into a smaller volume, its surface is nearer its centre and the gravitational pull on that surface is stronger. Anything on the surface of a large body is in the grip of gravity, and in order to escape it must move rapidly. If it moves rapidly enough, then even though gravitational pull slows it down continually it can move sufficiently far away from the body so that the gravitational pull, weakened by distance, can never quite slow its motion to zero. The minimum speed required for this is the ‘escape velocity’. Extract D

What is a black hole?

Loosely speaking, a black hole is a region of space that has so much mass concentrated in it that there is no way for a nearby object to escape its gravitational pull. Since our best theory of gravity at the moment is Einstein’s general theory of relativity, we have to delve into some results of this theory to understand black holes in detail, but let’s start of slow, by thinking about gravity under fairly simple circumstances. Suppose that you are standing on the surface of a planet. You throw a rock straight up into the air. Assuming you don’t throw it too hard, it will rise for a while, but eventually the acceleration due to the planet’s gravity will make it start to fall down again. If you threw the rock hard enough, though, you could make it escape the planet’s gravity entirely. It would keep on rising forever. The speed with which you need to throw the rock in order that it just barely escapes the planet’s gravity is called the ‘escape velocity.’ As you would expect, the escape velocity depends on the mass of the planet: if the planet is extremely massive, then its gravity is very strong, and the escape velocity is high. A lighter planet would have a smaller escape velocity. The escape velocity also depends on how far you are from the planet’s center: the closer you are, the higher the escape velocity. The Earth’s escape velocity is 11.2 kilometers per second (about 25,000 m.p.h.), while the Moon’s is only 2.4 kilometers per second (about 5300 m.p.h.). Now imagine an object with such an enormous concentration of mass in such a small radius that its escape velocity was greater than the velocity of light. Then, since nothing can go faster than light, nothing can escape the object’s gravitational field. Even a beam of light would be pulled back by gravity and would be unable to escape. The idea of a mass concentration so dense that even light would be trapped goes all the way back to Laplace in the 18th century. Almost immediately after Einstein developed general relativity, Karl Schwarzschild discovered a mathematical solution to the equations of the theory that described such an object. It was only much later, with the work of such people as Oppenheimer, Volkoff, and Snyder in the 1930’s, that people thought seriously about the possibility that such objects might actually exist in the Universe. These researchers showed that when a sufficiently massive star runs out of fuel, it is unable to support itself against its own gravitational pull, and it should collapse into a black hole. Incidentally, the name ‘black hole’ was invented by John Archibald Wheeler, and seems to have stuck because it was much catchier than previous names. Before Wheeler came along, these objects were often referred to as ‘frozen stars.’ I’ll explain why below. Source Information: - Faber Book of Science 1995 (article by Isaac Asimov first printed in the Daily Telegraph 1979) The Young Scientist Book of Stars and Planets (1977) A2 EngLang Editorial Writing Black Holes Exercise

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Microsoft Encarta 98 Encyclopaedia http://cosmology.berkeley.edu/Education/BHfaq.html