Enb5 Ew - Black Holes Source Exercise

Editorial Writing ‘Black Holes’ The following three extracts give information about black holes. Information about the origin of the texts is given at the end of the activity. Match each extract to source information. Note the textual features that lead you to these conclusions. What differences are there and how might these be explained?

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’.

Source Information: -

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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) Microsoft Encarta 98 Encyclopaedia