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Fill in the gaps with the proper item



1. She ____ understand Korean very well, but she ____ speak it perfectly.

a) be able to / cannot

b) is able to / is able to

c) is able to / cannot

2. When Olha was young, she ____ type quickly. She took a typing class and now she ____ type very quickly!

a) can / could

b) could not / can

c) could not / can to

3. ____ you play the piano when you were a child?

a) May

b) Could

c) Can

4. Nina ____ Italian food and she ____ French food too!

a) can cooking / can cooking

b) can cook / is able to cook

c) can cooks / can cooks

5. Peter ____ swim when he was a child, but now he ___. In fact, he swims every day!

a) could / can't

b) couldn't / can't

c) couldn't / can

6. We _____ get to the meeting on time yesterday, because the train was delayed by one hour.

a) couldn’t

b) can’t

7. I _____ drive a car until I was 34. Then I moved to the countryside, so I had to learn.

a) couldn’t

b) wasn’t able to

 

17. Fill in the gaps with can, can’t, could, couldn’t or was / wasn’t able to.

1. Like all simple machines, a lever ….. either give you more force or more distance, but as you get more of one you always give up some of the other.

2. Early men and women knew that a weight …... be pushed up a hill or a ramp of earth with less effort than would be required to move the same weight vertically.

3. A lever helps you do more work than you ….. do by yourself.

4. Wedges ….. be used for splitting open or pushing apart.

5. I had my hands full, so I ….. open the door.

6. When I was young, I ….. stand on my head.

7. Although he felt ill, he ….. finish all the paperwork.


UNIT 10

COMPLEX MACHINES

LEAD-IN

 

1. Look at the picture and say, what simple machines does a bike consist of?

 

2. In pairs, discuss what is meant by “complex machines”. Give examples of such machines.

READING

3. Read the text and match the questions (a-g) to the paragraphs (1-7):

a. What is a complex machine?

b. What kind of machines are inclined plane, wedge, screw, lever, wheel and axle, and pulley?

c. What makes an automobile a complicated complex machine?

d. Which simple machines are used in doorknobs and scissors?

e. What simple machines are used in a computer?

f. Which modern machines use gears?

g. What simple machines does a bicycle combine?

Complex Machines

 

You have already known about the six simple machines: inclined plane, wedge, screw, lever, wheel and axle, and pulley. You've probably figured out that these six machines were invented ages and ages ago. So what has been happening since then? Did someone invent simple machine number 7, 8, 9, 10, and so on?



 

Let’s look at a bicycle for an example. A bicycle is a much newer machine than the simple lever that a cave man used to move a big old rock, but it’s not as new as, say, a laptop computer. A bicycle is not number 7, or 100, or even 1000. A bicycle is actually a combination of several of those six basic simple machines. A bicycle gear is actually a combination of simple machines all by itself. A gear is a wheel, but the teeth on the gear are little wedges. What other simple machines can you find on a bicycle?

 

Gears, along with other simple machines, make up many of the machines you use every day. Some examples are the lawn sprinkler, a watch, and the gearbox in a car. Escalators and elevators use combinations of simple machines. So does a hand drill. So do sewing machines, parking meters, and windmills.

 

The doorknob is a wheel and axle system that transfers the force applied by a person to a system of levers. The levers move the bolt and unlatch the door. A pair of pliers is really two Class 1 levers with the same fulcrum (the pivot pin). A pair of scissors is a pair of pliers with wedges as the cutting edge.

 

Machines that use a combination of two or more simple machines are called complex machines. Machines can do all kinds of jobs today and make our lives easier in many ways.

 

Some complex machines are very complicated. An automobile is one such machine. The engine contains many levers, wheels and axles, and pulleys. The whole engine is held together by threaded bolts, which are a form of inclined plane. The transmission uses gears, which are a form of wheel and axle with specially shaped teeth on the outside of the wheels. Two gears fit together and transfer force and power from one gear shaft to another. By choosing the size of the gears, the speed and direction of the rotation of the axles can be controlled.

 

Even devices that do not seem to be mechanical use simple machines. A computer, which is thought of as an electronic device, has a cooling fan. This fan is a complex machine in which the motor shaft turns the fan, which is a form of wheel. The disk drive uses a wheel and axle to turn the disk and a system of levers to position the heads that read and write the data on the disk.

 





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