THE ESCAPE VELOCITY
Study the passage. Mind the underlined grammar points.
As far as I know, the first person to discuss black holes was a Cambridge man called John Mitchell, who wrote a paper about them in 1783. His idea was this. Suppose you fire a cannon-ball vertically upwards from the surface of the earth. As it goes up, it will be slowed down by the effect of gravity. Eventually, it will stop going up and will fall back to the earth. If it started with more than a certain critical speed, however, it would never stop rising but would continue to move away. This critical speed is called the escape velocity. It is about 7 miles a second for the earth, and about 100 miles a second for the sun. These velocities are greater than the speed of a real cannon-ball, but they are much smaller than the velocity of light, which is 186,000 miles a second. This means that gravity does not have much effect on light; light can escape without difficulty from the earth or the sun. However, Mitchell reasoned that it would be possible to have a star that was both massive and small in size so that its escape velocity would be greater than that of light. We would not be able to see such a star because light from its surface would not reach us; it would be dragged back by the star’s gravitational field. However, we might be able to detect the presence of the star by the effect that its gravitational field would have on nearby matter.
Light always travels at the same constant velocity. How then can gravity affect light?
According to general relativity, space and time together can be regarded as forming a four-dimensional space called space-time. This space is not flat; it is distorted or curved by the matter and energy in it. We observe this curvature in the bending of the light or radio waves that travel near the sun on their way to us. In the case of light passing near the sun, the bending is very small. However, if the sun shrinks until it is only a few miles across, the bending would be so great that light leaving the sun would not get away but would be dragged back by the sun’s gravitational field. According to the theory of relativity, nothing can travel faster than light, so there would be a region from which it would be impossible to escape. The region is called a black hole. Its boundary is called the event horizon. It is formed by the light that fails to get away from the black hole but stays hovering on the edge.
Stephen Hawking
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Vocabulary Notes
1.to reason – to come to a particular conclusion by thinking carefully
2.to affect something – to influence something
3.sufficiently – adequately – enough
4.to regard – to consider
5.to distort – to curve – to deform – a curvature
6.to shrink – to become smaller – to contract
7.to bend – when something bends it changes its shape to form a curve
8.to hover – to stay in the same position
9.an edge – the physical limit of an object or place
POST-READING TASK
(To be done at home in writing) I. Complete the sentences.
1.The first person .. …. … … was John Mitchell.
2.He wrote .. … about them in ….
3.When you fire a cannon-ball it … .. … … by the effect of gravity.
4.Eventually, it … … … .. and ... … … to the surface of the earth.
5.But if it started with a certain critical speed it .. … … …
6.The critical speed is called … … …
7.The critical speed is … .. .. . .. .. .. ..
8.It is … … … for the sun
9.This means that gravity … … … … .. light.
10.But the escape velocity of a star which is … massive … small in size would be greater than …. of light.
11.The light from such a star … .. … … by the star’s gravitational
field.
12.But the star might be detected by .. … … .. … … … … … .. .. …
II. Make your own conclusion. |
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III. Give words close in meaning. |
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1. finally |
4. to consider |
2. to influence |
5. to deform |
3. so |
6. to contract |
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CLASS EXERCISES
Exercise 1 (in groups)
Checking up understanding
1.What was John Mitchell’s idea?
2.In what case would a cannon-ball continue to move away?
3.What is the critical speed called?
4.What is the critical speed for the earth?
5.If you compare the critical speed of a cannon-ball with the velocity of light what conclusion can you make?
6.Why would it be impossible to see a star which is both massive and small in size?
7.How can we detect the presence of such a star?
8.What is space-time in other words?
9.Why is space not flat?
10.How can gravity affect light?
Exercise 2 (do it yourself)
Study grammar point II and put the verbs into the passive.
1.The first paper about black hole (write) in 1783.
2.A cannon ball (slow down) by the effect of gravity.
3.This critical speed (call) the escape velocity.
4.Light from the star’s surface (drag back) by the star’s gravitational
field.
5.The presence of the star may (detect) by the effect that its gravitational field would have on nearby matter.
6.Light (not affect) by gravity.
7.A four-dimensional space (call) space-time.
8.This space (distort) by the matter and energy in it.
9.The curvature in the bending of the light or radio waves can (observe).
10.The region from which it is impossible to escape (call) a black
hole.
11.Its boundary (call) the event horizon.
12.The event horizon (form) by the light that fails to get away from the black hole.
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UNIT 5
THE THIRD PLANET FROM THE SUN
Earth is a minor planet going around a very average star in the outer suburbs of a fairly typical spiral galaxy.
PREREADING TASK
Study some grammar points.
I. The participle |
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The English verb changes in four forms: |
|
|
I |
II |
III |
to use (the infinitive) – used (the past simple) – used (the passive parti-
ciple) = нный |
IV |
|
using (the active participle) = ющий |
Ving (or Ved) characterizes the noun which it follows.
Study the sentences.
1.You can think of ordinary, real time as a horizontal line, going from left to right.
2.There might also be quite a number of very much smaller black holes scattered around the universe, formed not by the collapse of stars but by the collapse of highly compressed regions in the hot, dense medium that has existed shortly after the big bang, in which the universe originated.
3.One of the problems facing physicists is to make general relativity compatible with quantum mechanics.
4.The earth is trying to move on a straight line through space-time, but the curvature of space-time produced by the mass of the sun causes it to go in a circle around the sun.
II. We use modal verbs + have V3 to say that it was possible or highly probable in the past.
May, might, can, could + have V3 = possible (Russian – возможно
было).
Must + have + V3 = highly probable (Russian – вероятно было,
наверняка было)
Can’t, couldn’t + have V3 = hardly possible (Russian – вряд ли
было)
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Study the sentences.
1.The observations indicate that the early universe must have been non-turbulent.
2.Heavy elements could have been formed by nuclear synthesis of the early generation of nearby stars.
3.The pyramids of Egypt and ancient Peru couldn’t have been built by any known methods of engineering.
Give Russian correspondence:
relative to, to realize (to understand), fairly (rather), typical (usual), N + that, normally (usually), a few (some), before, to make (to force), by 1930s, the only (single), via (by means of), ordinarily (normally), eventually (finally)
EARTH IS A UNIQUE PLANET
Study the passage. Mind the underlined grammar points.
Earth is a unique planet which has everything for the development of life and human evolution: the unique composition of air, the unique properties of water, the unique mineral composition of soils which feed all the living things, the unique position relative to the sun, and even the unique position of the solar system in the galaxy (Milky Way). The solar system is about 60000 light years from the centre of the galaxy, the distance which protects life on the earth from rigid radiation of the galactic centre.
What do we know about our position in the Universe? In ancient times people believed that the earth was at the centre of the universe. Now we realize that we are among the many inhabiting a minor planet going around a very average star in the outer suburbs of a fairly typical spiral galaxy that is only one of a hundred billion galaxies we can see. We know now that we cannot claim any special position in the universe.
FYI
1.A spiral galaxy is an enormous pancake-shaped collection of stars and gas.
2.An eclipse of the sun is an occasion when the moon comes between the earth and the sun so that for a short time you cannot see part or all of the sun.
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