8. Divide the following infinitives into two columns and give their second and third forms.

To buy, to produce, to play, to be, to have, to become, to provide, to develop, to satisfy, to need, to take, to rise, to grow, to cost, to situate. To give, to get, to understand, to decide, to make, to compose, to divide, to do ,to learn, to reflect, to find, to say, to tell, to speak, to return, to sell.

Regular verbs Irregular verbs

to produce - produced to buy - bought – bought

Part 3. Simple and Complex Machines

1. Read the following words and word combinations:

wheel, discipline, inclined, defined purposes, lever, therefore, wedge, major division, pulley, encompassing, hydraulics, galaxies.

2. Read and translate the text:

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 (N)

• The wheel and axle (O)

• The lever (7)

• The pulley (U)

• The wedge ( V [single wedge]; X [double wedge])

• The screw (Y)

The letters are a mnemonic, because their shapes resemble the shapes of the simple machines.

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. 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.

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 its 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.

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. There was one person, however, who liked to invent machines that seemed to make work more complicated,' not easier. That man was Rube Goldberg. Mr. Goldberg was trained as an engineer; in college he might have learned about making some of the latest machines. Then he became interested in drawing and writing cartoons. Rube Goldberg cartoons showing crazy complicated machines doing simple tasks became popular everywhere.