Kneel for the second chapter of the eighth grade scientific knowledge points of Zhejiang Education Press.

Grade 8 (1) Science Chapter II Review Outline

Section 1 Atmosphere

1. atmosphere: refers to the air layer around the earth at a height of about 1000 km above the earth.

2, the importance of the atmosphere: if there is no atmosphere, Earth A, there will be no weather change; B, no sound; ; C, vulnerable to meteorite attacks; D, the temperature difference is very large.

3. Stratification of atmosphere: According to the vertical distribution characteristics of atmospheric temperature, atmospheric density and material composition, the atmosphere can be divided into five layers-

Troposphere, stratosphere, mesosphere, warm layer and outer layer.

4. Troposphere: the bottom layer of the atmosphere, which is most closely related to human life and production.

* key memory: a, the most prominent feature of the troposphere-strong convective movement,

Law of air convection;

B, all kinds of complicated weather phenomena (such as clouds, rain, snow, lightning, etc. ) occurs in the troposphere;

* The troposphere concentrates 3/4 of the earth's atmospheric mass, and almost all water vapor and solid impurities.

C, the troposphere thickness is uneven, which shows that the thickness of the poles is small and the thickness of the equator is large.

* Small problem: 1. Household wall-mounted air conditioners are generally installed on the upper part of the room wall. Why?

A: In summer, the air blown out by air conditioners has low temperature and high density, which will sink, so that the air between rooms will form convection and the temperature of the whole room will be uniform.

5. Stratosphere: The atmospheric temperature rises gradually with the increase of altitude, and the airflow is stable, which is conducive to high-altitude flight; There is an ozone layer in it, which can absorb ultraviolet rays and protect human beings.

Section 2 Weather and Temperature

How's the weather?

Weather refers to the comprehensive situation of atmospheric temperature, humidity, air pressure and other factors near the ground in a short time.

The main differences between describing weather and climate are: weather refers to the atmospheric conditions in a short time; Climate refers to the long-term average atmospheric conditions.

* Weather: Clear skies Wan Li climate: rainy in winter and dry in summer.

2. Weather consists of many factors, among which the main ones are temperature, air pressure, wind, humidity and precipitation.

3, temperature-that is, the temperature of the air A temperature is the basic element of the weather; B tool for measuring temperature: thermometer;

C\ Commonly used temperature measurement unit: 0C D The temperature is always changing. During meteorological observation, put the thermometer in the louver for observation.

Reason: (1) The temperature inside the louver is lower than that outside the louver; (2) The temperature fluctuation in the louver is small, which can better reflect the real temperature.

E\ The highest temperature in a day usually appears around 2 pm; The lowest temperature in a day usually appears around sunrise.

F\ The most comfortable temperature for human body is: 220C C..

The third quarter atmospheric pressure

1, atmospheric pressure exists.

The atmosphere will exert pressure on the objects in it in all directions.

Specific example: (1)* Cover the cup filled with water tightly with paper and hang it upside down in the air so that the water will not flow out.

* Why can't the liquid in the dropper drip down? * Why does the hook suck on the wall?

Reason: They all use the principle of the existence of atmospheric pressure, and external atmospheric pressure >: internal atmospheric pressure leads to atmospheric .................... (answer mode).

(2) fountain pen absorbs ink; Suction of drinks through straws and dust removal by vacuum cleaners.

Reasons: Using the principle of atmospheric pressure, by reducing the local pressure, the substance continuously flows from the place with high pressure to the place with low pressure;

(3) Injecting drugs intravenously with a bottle is, why did the doctor insert another needle in the rubber stopper of the medicine bottle?

Reason: After the liquid medicine drops out, the air pressure inside will become smaller and the pressure will be too small. Under the action of atmospheric pressure, the liquid medicine can no longer drip out. After the needle is inserted, the air in the bottle can be replenished in time, so that the pressure of the air in the bottle is roughly equal to the external pressure, so as to ensure the continuous drip of the liquid medicine.

A. Experiments in the hemisphere of Fort Madre: It is proved that atmospheric pressure exists and is very large.

2, the size of the atmospheric pressure:

A, standard atmospheric pressure p = =1.01*105pa (atmospheric pressure at sea level), that is, 760mmhg.

B, the size of the atmospheric pressure is often used to measure the empty box barometer or mercury barometer.

C, the size of the atmospheric pressure is directly related to the density of the atmosphere, so the higher the ground, the smaller the atmospheric pressure;

D, there is also pressure in the human body to offset the atmospheric pressure in vitro.

3. Relationship between flow rate and pressure

The pressure of gas (liquid) will decrease with the increase of flow rate.

Specific example: (1) When the train is running at high speed, people can't get too close to the rails. Why?

Cause: The speed is high, the pressure is low, and the atmospheric pressure far away from the rail is greater than that near the rail, which will be pushed to the rail by the atmospheric pressure, which is very dangerous.

(2) When two ships run in parallel, keep a certain distance;

(3) Put the ping-pong ball into the funnel and blow air into the funnel to prevent the ping-pong ball from falling; (4) When an airplane flies, the airflow speed on the upper side of the wing is faster than that on the lower side, so the air pressure on the upper side of the wing is smaller than that on the lower side.

The fourth quarter atmospheric pressure and human life

1 and the influence of atmospheric pressure on the weather

A\ At the same altitude, the atmospheric pressure in different areas may not be the same; The same height, the same area and the atmospheric pressure at different times are not necessarily the same;

B\ At the same height, the area with high air pressure is called high pressure area, and the area with low air pressure is called low pressure area.

C\ High pressure area: sunny weather and dry air; Low pressure area: rainy weather, cloudy sky.

2. The influence of atmospheric pressure on human body

A, mountain reaction B, cupping principle C, when the plane is flying at high altitude, the cabin must be pressurized; Astronauts must wear pressurized spacesuits when walking in space.

3. The influence of atmospheric pressure on the boiling point of liquid

A, when the air pressure increases, the boiling point of liquid increases; b, when the air pressure decreases, the boiling point of liquid decreases.

Specific examples: * In mountainous areas, it is difficult to cook in ordinary pots (reason: in the mountains, the air pressure is reduced and the boiling point is lowered)

* the use principle of pressure cooker

4, daily necessities and atmospheric pressure

A. vacuum compression fresh-keeping bag

B. vacuum cleaner: a cleaning tool that works at atmospheric pressure.

Principle: The fan impeller is driven by the motor to rotate at high speed, so that the air can be discharged at high speed, resulting in an instantaneous vacuum inside the vacuum cleaner and a pressure difference with the external atmospheric pressure. Under this action, the air containing dust is sucked in and filtered by the dust filter to discharge clean air. The greater the pressure difference, the stronger the capacity of the vacuum cleaner.

Section 5 wind

1, how is the wind formed?

A, the wind is the horizontal movement of air;

B wind: it flows from the high pressure area to the low pressure area.

2. Two basic elements of wind: wind direction and wind speed.

Wind direction-the direction in which the wind blows. There are eight commonly used wind directions, which are represented by easterly winds.

Weather vane is often used to observe the wind direction in meteorological observation.

B, wind speed-the distance that air flows in unit time, unit: m/s.km/h.

Wind speed is usually expressed by wind scale, which is 0- 12. In meteorological observation, anemometers are often used to observe wind speed.

3. the relationship between wind and human beings: a. beneficial-wind is a resource that can be used for power generation, navigation and sports;

B, unfavorable-destructive wind will be dangerous to human beings.

Section 6 Why does it rain?

1, air humidity: the amount of water vapor in the atmosphere. Generally expressed by relative humidity.

(1) Relative humidity: indicates the richness of water vapor in the air;

Common percentage (%)

(2) Relationship between air humidity and temperature: The higher the temperature, the more water vapor the air can hold. So air humidity is a relative concept.

(3) The instrument for observing humidity is a hygrometer, and the most commonly used hygrometer is a wet and dry bulb hygrometer, which is essentially two special thermometers.

(4) Measure with a wet and dry bulb hygrometer, and then check the relative humidity table to get the relative humidity.

(5) Relationship between air humidity and weather: The greater the humidity, the richer the water vapor in the air, and the greater the possibility of cloud formation and precipitation.

(6) Weather proverb: "Swallows fly low, it will rain"-Before the rainstorm, the air humidity is high, the wings of insects become soft and fly low, so swallows fly low for food.

Step 2 precipitate

(1) Formation conditions of precipitation: a. The relative humidity of air reaches 100%.

B, the temperature continues to drop, and the ability of air to contain water vapor decreases; Water vapor condensation

There is tiny dust in the air.

I.e. clouds, fog, etc.

D. Water droplets and ice crystals are large enough to fall to the ground.

(2) Precipitation: including rain, snow and hail. The most common precipitation is rainfall.

(3) Rainfall: refers to the depth of water in a certain period of time.

Unit of measurement-mm; Measuring instrument-rainfall tube

What will the weather be like tomorrow?

1, there are generally three ways to get the weather forecast:

(1) By watching TV, listening to radio and other media or weather forecast;

(2) Forecast the weather by analyzing the weather map;

(3) Make your own weather forecast through meteorological observation.

2. What do you think of the weather forecast?

(1) cloudy "means that the total cloud amount in the sky is above 8/ 10, and" cloudy "means that the total cloud amount in the sky is between 5/ 10 and 7/ 10.

"Partly cloudy" means that the total cloud amount in the sky is between 5/ 10 and 3/ 10, and "sunny" means that the total cloud amount in the sky is below 3/ 10.

(2) Light rain: the precipitation is less than 5mm within 12 hour, and moderate rain: 5- 15mm within 12 hour.

Heavy rain: within 12 hours, the precipitation is greater than15 mm.

The probability of precipitation indicates the possibility of precipitation.

3. Weather chart

(1) Common weather systems: high pressure system, low pressure system, cold front system and warm front system.

(2) The relationship between common weather systems and weather:

A. High voltage system: sunny day; B. Low pressure system: rainy weather.

C, cold and warm front system: the weather changes on the front are more complicated.

Cold front: the front where cold air moves to the side of warm air, which often brings rainfall, strong wind and cooling weather;

Warm front: a front where warm air moves to the cold air side, usually bringing rain and warm weather.

Cold front warm front

(3) Special weather system: typhoon-actually it belongs to a strong and low pressure system.

Section 8 Climate and Factors Affecting Climate

1 climate

(1) Meaning of climate: Climate refers to the weather characteristics in a certain area for a long time, including average and extreme weather conditions.

(2) Weather and climate:

A, difference: short time and long time;

B. Contact: The average and extreme weather conditions are climate.

Such as: long summer without winter, crisp autumn and so on. Autumn is crisp in most parts of our country, but it doesn't mean it won't rain.

2. Factors affecting climate:

The influence of (1) latitude on climate.

Large areas with different latitudes receive different amounts of solar radiation, and their temperature zones on the earth are also different.

Latitude of China: mainly in the north temperate zone, and a few areas in the south are in the tropics.

Example: Hainan, the southernmost tip of China, has low latitude, high temperature and long summer without winter; Mohe, the northernmost river in China, has high latitude, short summer and long and cold winter. -that is, the influence of latitude position on climate.

(2) The influence of ocean and land properties on temperature and precipitation.

A. Specific heat: We refer to the heat absorbed by a substance with a unit mass of 1 when it rises to 1℃ as the specific heat capacity of this substance, which is abbreviated as specific heat.

Unit of specific heat: coke/(kg). ? C) Pronunciation: Coke symbol per kilogram Celsius: j/(kg? ℃)

Specific heat of water: 4.2× 103 J/(kg? ) What is it?

Meaning-1kg water temperature rise 1℃, the heat to be absorbed is 4.2× 103 joules.

Reading of specific heat meter: (1) The specific heat of water is the largest. This shows the role of water as a coolant and heat preservation agent.

⑵ The specific heat of different substances is different. So specific heat is a property of matter. It has nothing to do with the quality of matter, the rise of temperature and the absorption and release of heat.

(3) The specific heat of the same substance is different in different states, indicating that the specific heat is related to the state of the substance.

C. sea and land at the same latitude:

Temperature: In winter, the temperature drops rapidly on land and slowly on the ocean.

In summer, the land temperature drops rapidly and the ocean temperature drops slowly.

Reason: The nature of ocean and land is different.

Precipitation: there is more precipitation along the coast, with a relatively uniform seasonal distribution, less precipitation in the inland, and precipitation is concentrated in summer.

Reason: The distance from the ocean is different.

(3) The influence of monsoon on climate

A. Definition: In different seasons, the wind direction is opposite and almost opposite.

B, the root cause of monsoon: the nature of ocean and land is different.

C, wind direction:

Summer-when the summer monsoon blows, the wind blows from the ocean to the mainland (in summer, the land temperature is high, the air pressure is low, the ocean temperature is low, the air pressure is high, and the wind blows from the high pressure area to the low pressure area).

Winter and winter wind blows, and the wind blows from the land to the sea (in winter, the land temperature is low, the air pressure is high, the ocean temperature is high, the air pressure is low, and the wind blows from the high pressure area to the low pressure area).

D Nature: The northerly winds prevail in winter, so it is dry and rainy, and the southerly winds prevail in summer, so it is wet and rainy.

E there are many monsoon regions in the world, and the Asian monsoon is the most popular. China has the most remarkable monsoon climate in the world.

(4) the influence of topography on climate

A, the temperature decreases with the elevation of the terrain.

Generally, when the altitude rises 1000m, the temperature will drop by about 6℃.

B, the windward slope of the mountain-rainy, Leeward slope-little rain

C The city with the most precipitation in China: Huoshaoliao, Taiwan Province Province.

Reason: The city is located on the windward slope on the east side of the mountains in Taiwan Province Province, with abundant terrain and precipitation.

Section 9 monsoon in eastern China and arid climate in western China

1, monsoon climate in the east

(1), monsoon climate zone: refers to the area that summer monsoon can reach. Precipitation mainly comes from the humid summer monsoon.

(2) The scope of monsoon climate zone: the areas east and south of Daxinganling-Yinshan-Helan-Gangdise Mountain in China.

(3) Monsoon climate types: tropical monsoon climate, subtropical monsoon climate and temperate monsoon climate.

(4) Main features of monsoon climate in China:

Winter: low temperature and little precipitation;

Summer: high temperature and heavy precipitation,

There is abundant rainfall throughout the year. However, the winter temperature in the south is obviously higher than that in the north, with small annual temperature difference and large annual precipitation.

(5) Monsoon climate has advantages and disadvantages for people's production and life.

First, the precipitation is abundant, concentrated in summer, with four distinct seasons, and the rain and heat are very beneficial to agricultural production.

B, China is a continental monsoon climate, and the annual precipitation changes greatly, which makes floods and droughts frequent in China.

D, low temperature in winter often leads to cold wave, freezing injury, blizzard and other bad weather.

(6) Shenzhen has a subtropical monsoon climate, which may cause meteorological disasters such as typhoons, droughts and floods.

2. The arid climate in western China.

(1) Arid and semi-arid climate zone: refers to the western part of China where summer monsoon cannot reach, and precipitation is generally scarce.

(2) Characteristics of arid climate in western China:

The annual precipitation is scarce, concentrated in summer, and varies greatly with the seasons.

It is hot in Leng Xia in winter, and the daily temperature difference is greater than the annual temperature difference, but there is plenty of sunshine.

(3) Advantages and disadvantages of arid climate:

Large temperature difference and long illumination time are very beneficial to agricultural production, such as the production of cotton and melons and fruits.

(4) Adaptability of organisms to arid climate zones in behavior and morphology:

Why is the stem of cactus so thick that its leaves become thorns?

In order to adapt to the arid climate, thick stems are beneficial to water storage, and leaf thorns can reduce water evaporation.

Mustard bugs in the desert climbed to the top of the sand mound on foggy nights, raising their hips high. What is the reason?

Let the water condensed on the body flow along the body to the mouth, which is the main way for them to get water.

3. Major meteorological disasters in China-cold wave, typhoon and flood.

(1) Cold wave is a large-scale strong cold air activity, which is caused by strong cold and high pressure activity.

Hazard: bring severe cooling, frost, strong wind and sand blowing.

(2) Typhoon is a kind of disastrous weather with great destructive power.

Hazard: A, strong wind; B. heavy rain; Storm surge,

Favorable: In the dry season, typhoons will bring abundant precipitation and help alleviate the drought.

(3) Flood is one of the most harmful natural disasters in China.

Natural causes: continuous precipitation, typhoon.

Man-made reasons: human activities, such as: destroying vegetation, reclaiming land from lakes, encroaching on rivers, disorderly development of cities, etc.

4. Impact of human activities on climate

(1) Human activities are closely related to climate.

A. Human activities conducive to climate improvement: afforestation, reservoir construction, large-scale agricultural irrigation, etc.

B. Human activities causing climate deterioration: destroying vegetation, emitting a lot of harmful substances and overgrazing.

(2) Greenhouse effect-refers to the trend that due to some natural or man-made reasons, the carbon dioxide in the atmosphere is increasing, the insulation of the atmosphere to the ground is enhanced, and the global temperature is warming.

Man-made reasons: consuming a lot of energy; Destroy the forest

(3) Urban "heat island" phenomenon-a heating mass with a higher temperature than the surrounding suburbs is often maintained over the city.