19Unit Seven

GRAVITATION
READING PASSAGE
There is no gravitational pull . . . only a push!
This hypothesis provides a general model for the mechanics of gravitation. It in no way
refutes the observed behavior of gravitation, but merely seeks to explain it. I have based all
but a single aspect of this model on established scientific knowledge, and that single aspect
is my prediction of an unknown. (So it remains to be proved or disproved.)
The team of medieval physicists stepped out of the time machine and began to examine
the strange, new device fastened to the window. They had never before seen a suction cup, so
with great enthusiasm, they began to experiment by pulling this mysterious device off the
window, then reattaching it. "The glass must attract the device" remarked one of them. They
all nodded in agreement.
Next, they found a smaller piece of glass and discovered that the suction cup had the
gripping power to suspend it. This new revelation prompted another physicist to remark, "The
device must also attract the glass!" Having no real reason to seek a better explanation than this
for their observations, the team of medieval physicists unanimously concurred, and a new
theory was born: "The device and the glass are attracted one to another, this being a
characteristic of space!"
My comparison to medieval science is not an insult to physicists. I merely wish to
emphasize mankind's present level of ignorance of the mechanics of our universe. We now
know that the suction cup in this example is held to the glass by air pressure. The invisible
molecules that make up air constantly bombard the surfaces of the glass and the suction cup.
The difference in pressure cause, what appears to be, an attraction. My gravitational
hypothesis is somewhat similar. All I ask of you, the reader, is to keep an open, yet discerning
mind.

3. ………….The writer has recognized something else about the model.
4. ………….The medieval physicists had never known of the force of attraction.
5. ………….We, human beings now have not got enough knowledge of the mechanics
of our universe.
6. ………….It’s natural that the glass and the suction cup attract each other.
7. ………….The attraction between the glass and the suction cup is due to air pressure.
8. ………….We all should have an intuitive mind towards the phenomenon of
gravitation.
Exercise 3: Find the word(s) or phrase(s) in the text with the meaning similar to those given
bellow:
1. operation …………………………
2. factor …………………………
3. already-known …………………………
4. got out of …………………………

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5. tied to …………………………
6. to look into …………………………
7. to hang …………………………
8. cause to response …………………………
9. to agree …………………………
10. witness …………………………
11. feature …………………………
12. to attack …………………………
GRAMMAR IN USE
A) Modal verbs to express certainty or possibility
1. Certainty
To express certainty (or to say that something is certainly true or untrue), we use will,
must and can’t.
1.1. For present and future situations, we use:


Example:
1. The experiment will have been conducted by now.
2. The ball is moving. Someone must have kicked it.
3. Newtonian mechanics can’t have worked in that case. The interacting bodies were on
the scale of atomic structure.
Note: In questions, we normally use can or will.
Example: Can it really be true?
How will it be done?
2. Possibility:
2.1. We use: may /might + verb base
to say that something is possibly true or an uncertain prediction.
Example:
1. We may find g by simply weighing a standard weight on a spring balance.
2. There might be an error somewhere in the procedures.
Note: There is almost no difference in meaning, but may is a little stronger than
might.
2.2. To lay emphasis on the continuation of the action, we can use
may /might + be + V_ing
Example:
1. He may/might be doing well in Physics because he has borrowed a lot of books on
Physics from the library.
2.3. The perfect can be used also:
may /might + have + P
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Example:
1. He may/might have made a lot of observations before reaching such a conclusion.
Note: These two verbs can not be used in questions. Can and will are used, instead.

However, this formula _____ be used only when the height h is much smaller than
the Earth’s radius.
6. How ______we ensure that a body thrown from the Earth will not return to the
Earth?