English for students of Physics_Unit 7

19


Unit 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.

(From )
EADING

COMPREHENSION

Exercise 1: Answer the following questions by referring to the reading passage
1. What does the writer mean by ‘this hypothesis’?

20
…………………………………………………………………………………………
………………………………………………………………………………
2. How does the hypothesis work?
…………………………………………………………………………………………
………………………………………………………………………………
3. What did the medieval physicists do with the suction cup when they first saw it?
…………………………………………………………………………………………
………………………………………………………………………………
4. What did they think happenedto the suction cup?
…………………………………………………………………………………………
………………………………………………………………………………
5. What really happens in the case?
…………………………………………………………………………………………
………………………………………………………………………………
Exercise 2: Decide whether the writer would agree to each of the following statements. Write (Y)
for the agreed ones, (N) for the disagreed ones and (Mb) for the ones which the writer may or
may not agree to.
1. ………….The hypothesis gives a thorough explanation for the phenomenon of
gravitation.
2. ………….The writer did rely on all the existing knowledge of gravitation to explain
the model of experiment.

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 …………………………

21
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:

will, must and can’t + Verb base
In which:
a. will is used when the speaker means that something is certainly true, even though we
can not see that it is true.
Example:
1. He has finished his report on the spin-transfer effects. ~ It’ll earn him world-wide
fame.
2. If a body is at rest, It will remain at rest.
Note: will is often used in its contracted form ‘ll
b. Must is used when the speaker sees something as necessarily and logically true.
Example: The glass must attract the device.
The device must also attract the glass.
You can see the contexts of the two above statements from the reading passage.
c. Can’t is used when the speaker sees it as logically impossible for something to be true.
Can’t and must are opposites.
Example: It can’t be explained how to measure mass by imagining a series of
experiments. ~ There must be some experiments to be conducted.
Or we can use:

22
will, must and can’t +be +V_ing
to lay emphasis on the continuation of the action.
Example:
1. Where’s Jane? ~ She’ll be working in the lab. (I expect)
2. In general, if our standard body of 1kg mass has an acceleration a, we know that the
force F must be acting on it.
3. The ball can’t be moving . It must be at rest because there’s no force acting on it.
1.2. For a perfect situation, we use:
will, must and can’t + have +P
II

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
II

23
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.

(Refer to (1))
For all the above verbs, we follow the rule of making negation or interrogation for modal
verbs in general.
B) Past perfect tense
Read the following passage:
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, and then reattaching it. In the second sentence, the writer uses the past perfect tense
of the verb to see to mean that this action happens before the actions expressed by to step and
to begin which were conjugated in past tense. This is the use of the past perfect tense.
We form the tense with: had + P
II
To express an action or a state before a past time reference.
Examples: Everything had been good before he put his nose in.
Before quantum physics, the interacting bodies on the scale of atomic
structure had not been able to explain.
PRACTICE

Exercise 1: Fill in the blank with will; can; must; can’t; may or might
1. Suppose that Earth pulls down on an apple with a force of 0.80N. The apple_______
then pull up on Earth with a force of 0.80N.
2. A particle of mass m, located outside Earth a distance r from Earth’s center, is
released, it _____ fall towards the center of Earth.
3. An object located on Earth’s surface anywhere except at the two poles _____rotate in
a circle about the rotation axis and thus ______ have a centripetal acceleration that
points towards the center of the circle.
4. For an object situated in an underground laboratory, force of attraction ______be
exerted on it by the internal and external layers of the Earth.
5. A body raised to a height h above the Earth possesses a potential energy of mgh.

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?