Put disjunctive questions to the sentences.

1. They are going home from university, …..?

2. The exam wasn’t difficult, …..?

3. You have cleaned your bike, …..?

4. You have to get up early, …..?

5. We write, read and speak English during the lessons, …..?

6. There were a lot of students at the lecture, …..?

7. You can't swim very well, …..?

Write questions to which the words in bold are the answers.

1. Each planet has its own gravity

2. Here on Earth we measure gravity using a scale.

3. The coefficient of friction for two materials may differ depending on the type of friction involved.

4. Other types of friction include rolling friction and fluid friction.

5. Scientists often like to use the word mass instead of weight.

6. MRI machines in hospitals use magnetism to make a picture of the inside of your body.

7. Invention of electronic computers is one of the greatest achivements of mankind.

17. Work in pairs. Make up 5 questions to the text “Gravity, Friction, Magnetism” and let your partner answer them.

UNIT 9

SIMPLE MACHINES

LEAD-IN

1. In pairs, discuss what is meant by “simple machines”. Are they still in use today? If yes, give some examples.

2. What simple machines can you see in the picture? Which one is missing?

READING

3. Read the text about simple machines and complete the following sentences:

1. A …. looks a lot like a wheel and axle with a rope over it.

2. A …. is a bar with a balance point called the fulcrum.

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

4. A nail is a familiar form of the …. .

5. The …. was the probable method employed by the Egyptians for manipulating into place the huge blocks of stone in the pyramids.

6. The …. is a triangle with two chief surfaces that meet in a sharp angle or taper to a thin edge.

7. The mechanical engineer more frequently uses the …., a spiral form of the inclined plane.

Simple Machines

In physics, a simple machine is any device that only requires the application of a single force to work. Work is done when a force is applied and results in movement over a set distance. The work done is the product of the force and the distance.

The traditional list of simple machines is:

- The inclined plane

- The wheel and axle

- The lever

- The pulley

- The wedge

- The screw

These simple machines have something in common. It's easy to see how the wheel and axle and the pulley are related; a pulley looks a lot like a wheel and axle with a rope over it. This simple device was used in ancient times for tasks such as raising water from wells or streams and hoisting sails onto ships.

A lever doesn't look much like a wheel and axle or a pulley. For starters, it isn't even round! So you may be surprised to learn that the lever is the basic simple machine that the other two are based on.

A lever is a bar with a balance point called the fulcrum. A garden shovel is an example. In a wheel and axle, the fulcrum is in the center. A lever helps you do more work than you could do by yourself. It seems like it makes you stronger, but it really doesn't. Like all simple machines, a lever can either give you more force or more distance, but as you get more of one you always give up some of the other. Levers are also used just to change the direction of a force.

The three remaining simple machines are so related to one another that they are sometimes grouped together. They are the wedge, the inclined plane, and the screw.

The wedge is a triangle with two chief surfaces that meet in a sharp angle or taper to a thin edge. Wedges are used for splitting open or pushing apart. They were used from very early times for such purposes as quarrying rock, plowing fields or cutting wood, as with an axe. A nail is a familiar form of the wedge.

The inclined plane was the probable method employed by the Egyptians for manipulating into place the huge blocks of stone in the pyramids. Early men and women knew that a weight could be pushed up a hill or a ramp of earth with less effort than would be required to move the same weight vertically. The inclined plane is an important factor that concerns civil engineers when designing highways or railroads.

The mechanical engineer more frequently uses the screw, a spiral form of the inclined plane. Today we are most familiar with the screw as a fastener but it has numerous other uses. A familiar adaptation is the screw jack used to lift automobiles or any great weight through a short distance.

Date: 2015-12-11; view: 1348