1. The gases: features

   - Gases take up space. In the first left picture, we can see that in the reversed glass, the air takes up space and displaces the liquid.

   - Gases expand, that is, they tend to take up the maximum volume. In the second picture, when we open the perfume bottle, the gas particles escape in all directions.

   - Gas particles have high mobility, they move in all directions.

   - - Gases weigh. In the third picture, we can weigh the ball before and after inflate it. The difference is the weight of the air that we injected.

   2. Answer if these sentences are true or false:

Gases do not weigh

Gases expand

Gases do not take up space

Gas particles have mobility

    3. The air

   The earth is surrounded by a blanket of air, which we call the atmosphere.

   The air is comprised of several gases mixed in various proportions. The main gases are:

   - Oxygen: active gas, which occupies 21% by volume of dry air.

   - Nitrogen: it occupies 78% and moderates the energetic action of oxygen.

   - Noble gases: such as argon with 0.9%.

   - Carbon dioxide (CO2): with 0.03 %. Plants need it to make the chlorophyll function.

   - Water vapor: it creates clouds, and because of the precipitation, it causes rain, snow or hail.

   The atmosphere is the layer of air that surrounds the Earth and it makes life possible. We can distinguish several layers:

   - Troposphere (from 250 m to 12-15 Km altitude): where all weather takes place. When we ascend into the troposphere, the temperature and the oxygen decrease.

   - Stratosphere (15 to 50 km): where the temperature is very low. It is constantly around 70 degrees below zero.

   - Ionosphere: it regulates the amount of solar radiation that reaches the lower layers.

   4. Indicate if these sentences are true or false:

Oxygen is the most voluminous

Carbon dioxide occupies 0.9%

Nitrogen occupies 78%

Stratosphere is the lower layer

Oxygen is an active gas

    5. Winds

    When the air heats up, its volume increases, therefore its relative weight (density) decreases. When the air cools down, it contracts and consequently its relative weight (density) increases. Therefore, there is little atmospheric pressure in the hot spots of earth and great pressure in cold spots.

   Winds are air currents caused by the difference of pressure between two points on the surface of earth. The winds always blow from high pressure areas (anticyclone) to low pressure areas (depression).

   6. Answer if these sentences are true or false:

When the air heats up, the volume decreases

Cold air is heavier

There is a lot of pressure in hot spots

Anticyclone has high pressures

Depression has low pressures

    7. Wind power

   Wind power is produced by the win. It is used to navigate at full sail, to move the windmills, to extract water from wells and other uses.

   Currently we use the wind power to produce electricity. It has the same advantages of solar and hydro power: it is inexhaustible, free and does not pollute.

   8. Answer if these sentences are true or false:

Solar power is used to navigate at full sail

Wind power produces electricity

Wind moves the windmills

Solar power pollutes

Wind power is inexhaustible

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®Arturo Ramo García.-Record of intellectual property of Teruel (Spain) No 141, of 29-IX-1999
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