Physical concepts in the first volume of the second day of junior high school

First, the generation of sound:

1, sound is produced by object vibration; People vibrate by vocal cords, bees by small black spots under their wings, wind by air, air columns in musical instruments control vibration, stringed instruments vibrate by strings, drums vibrate by drums, clocks vibrate by clocks and so on. );

2. When the vibration stops, it stops; But the sound did not disappear immediately (because the original sound continued to spread);

3. The sounder can be solid, liquid and gas;

4. The vibration of sound can be recorded and restored (making and playing records);

Second, the spread of sound.

1, sound transmission needs medium; Solid, liquid and gas can transmit sound; When sound propagates in a solid, the loss is minimal (sound propagates farthest in a solid and travels through the railway track). Generally speaking, sound travels fastest in solid and slowest in gas (except cork).

2, vacuum can't transmit sound, and astronauts on the moon (in space) can only talk by wireless phone;

3. Sound propagates in the form of waves (sound waves);

Note: the sound object must be vibrating, and the sound may not be heard when it vibrates;

4. Sound speed: the distance traveled by an object per second, in meters per second; The formula for calculating the speed of sound is v = s/t; The speed of sound in air is 340m/s;

3. Echo: In the process of sound propagation, it is reflected by obstacles and then reaches people's ears. When people hear the reflected sound, it is called echo (for example, the echo of mountains, the incessant thunder in summer, the echo wall of the Temple of Heaven in Beijing).

1. Conditions for hearing the echo: the time interval between the original sound and the echo is above 0. 1s (the teacher's echo can't be heard by the teacher, and the sound in the small room is louder because the original sound and the echo overlap);

2. Use of echo: measuring distance (car to mountain, depth of sea water, distance from glacier to ship);

Fourth, how to hear the sound.

1. Composition of human ear: The human ear is mainly composed of external auditory canal, tympanic membrane, ossicles, cochlea and auditory nerve;

2. The sound is transmitted to the ear canal, causing the tympanic membrane to vibrate, and then transmitted to the brain through the ossicles and auditory nerves to form hearing;

3. In the process of sound transmission to the brain, obstacles in any part will make people lose hearing (the obstacles in the eardrum and ossicles are conductive deafness; The disorder of auditory nerve is neurological deafness);

4. Bone conduction: it is transmitted to the auditory nerve without the help of tympanic membrane, skull and jaw, and then to the brain to form hearing (Beethoven listens to music after hearing loss, and we hear our own voice when we speak); The performance of bone conduction is better than that of air conduction;

5. Binaural effect: the distance between students and their ears is generally different, so the time, intensity and rhythm of sound reaching their ears are also different, which can be used to judge the sound source orientation phenomenon (auditory stereo);

5. The characteristics of sound include: tone, loudness and timbre;

1. Tone: the sound level is called the tone, and the higher the frequency, the higher the tone (frequency: the number of times an object vibrates per second, indicating the vibration speed of the object, in hertz, the larger the vibrating object, the lower the tone; )

2. Loudness: the strength of sound is called loudness; The greater the amplitude of the object, the stronger the loudness]; The farther the listener is from the speaker, the weaker the loudness;

3. Timbre: Although the timbre and loudness of different objects may be the same, the timbre must be different; (It depends on the timbre to distinguish what is the sound of object method)

Note: Tone, loudness and timbre are independent of each other.

Six, ultrasonic and infrasound waves

1. The human ear perceives sound in a frequency range: 20 Hz ~ 20000Hz, and above 20,000 Hz is called ultrasound; Below 20Hz is called infrasound;

2. The hearing range of animals is different from that of people. Elephants communicate through infrasound, and earthquakes, volcanic eruptions, typhoons and tsunamis all produce infrasound.

Seven. Harm and control of noise

1, noise: (! From a physical point of view, the sound made by an object when it vibrates irregularly is called noise; (2) From the perspective of environmental protection, all sounds that hinder people's normal study, work and rest and interfere with people's listening are noise;

2. Musical sound: from a physical point of view, the sound made when an object vibrates regularly;

3. Common sources of enrollment: the roar of planes, the whistle of cars, firecrackers and the friction between metals;

4. Noise level: The unit of sound intensity is decibel. Symbol dB, more than 90dB will be harmful to health; 0dB refers to the sound that the human ear can just hear;

5. Noise control: (1) The source of students is weak (muffler is installed); (2) in the process of transmission (planting trees. Sound insulation wall) (3) Weakening at human ears (wearing earplugs)

Eight, the use of sound

1. Ultrasonic wave has high energy and high frequency, and is used for diamond heads, watches and clocks and other precision instruments; Ultrasonic waves propagate basically in a straight line, and are used for echolocation (bat direction finding) products (sonar systems).

2, transmitting information (doctors check the "smell" of the disease, play B-ultrasound, knock on the rails to listen to the sound, etc. )

3. Sound can transmit energy (the glass near the airport is shattered, you can't speak loudly in the snowy mountain, a tuning fork vibrates, and the tuning fork that is not in contact vibrates).

Chapter II Propagation of Light

1. Light source: An object that can emit light is called a light source. Light sources can be divided into 1, cold light sources (jellyfish, energy-saving lamps) and hot light sources (flashlight, sun); 2. Natural light sources (jellyfish, sun) and artificial light sources (light bulbs, flashlights); 3. Biological light sources (jellyfish, axe fish) and abiotic light sources (sun, light bulbs)

Second, the spread of light.

1. Light travels in a straight line in the same uniform medium;

2, the application of straight-line propagation of light:

(1) pinhole imaging: the shape of the image has nothing to do with the shape of the pinhole, like an inverted real image (the spot in the shade is the image of the sun).

(2) Straight line: laser collimation (directional tunnel); Assemble the whole team; Shoot and aim;

(3) Restrict the line of sight: sit in the well and watch the sky (it is required to make an optical diagram of the frog's field of vision with or without water); A leaf is blind;

(4) the formation of shadow: shadow; Eclipse, eclipse (it is required to know that the moon is in the middle during the eclipse; The earth is in the middle during the eclipse)

3. Light: straight lines with arrows are often used to indicate the trajectory and direction of light;

Third, the speed of light.

1, the speed of light in vacuum is the fastest in the universe;

2. In the calculation, the speed of light in vacuum or air is c = 3×108m/s;

3. The speed of light is about 3/4c in water and 2/3c in glass;

4. Light year: it is the distance that light travels in one year, and the light year is the unit of length; 1 light year ≈ 9.46×1015m;

Note: Sound propagates fastest in solid, followed by liquid, slowest in gas and not in vacuum; Light travels fastest in vacuum, followed by air, and slowest in transparent liquids and solids (and vice versa). The speed of light is much faster than the speed of sound (if lightning is seen before thunder is heard, the time of sound propagation cannot be ignored in the 100m competition, but the time of light propagation can be ignored).

Fourth, the reflection of light:

1. When light strikes the surface of an object, some light will be reflected back by the object. This phenomenon is called light reflection.

We see objects that don't emit light because the light reflected by the objects enters our eyes.

3. Law of reflection: In the phenomenon of reflection, reflected light, incident light and normal are all in the same plane; Reflected light and incident light are separated on both sides of the normal; The reflection angle is equal to the incident angle.

(1), normal: a straight line perpendicular to the reflecting surface made through the incident point of light;

(2) Incident angle: the angle between incident light and normal; Reflection angle: the angle between the normal ray and the normal. (The incident light forms an angle θ with the mirror surface, the incident angle is 90-θ, and the reflection angle is 90-θ).

(3) There is a causal relationship between the incident angle and the reflection angle, and the reflection angle always changes with the change of the incident angle, so we can only say that the reflection angle is equal to the incident angle, but we can't say that the incident angle is equal to the reflection angle. (The mirror rotates θ, and the reflected light rotates 2θ)

(4) What is the incident angle and reflection angle equal to at normal incidence? A: At normal incidence, the incident angle is 0 degrees and the reflection angle is equal to 0 degrees.

4. In the reflection phenomenon, the light path is reversible (eyes look at each other).

5. Draw a general light path diagram by using the reflection law of light (required):

(1), determine the incident (reflection) point: the incident (reflection) point is the intersection of incident light and reflection surface or reflected light and incident light.

(2) Make a normal according to the fact that the normal is perpendicular to the reflecting surface.

(3) Draw incident light or reflected light according to the fact that the reflection angle is equal to the incident angle.

5. Two kinds of reflection: specular reflection and diffuse reflection.

(1) Specular reflection: When parallel light hits a smooth reflecting surface, the reflected light still reflects out in parallel;

(2) Diffuse reflection: When parallel light hits the rough reflecting surface, the reflected light will be reflected in all directions;

(3) Similarities between specular reflection and diffuse reflection: both are reflection phenomena, and both obey the law of reflection; The difference is that the reflective surfaces are different (one is smooth and the other is rough), and the incident light in one direction, the reflected light reflected by the mirror only shines in one direction (glare); And diffuse reflection is emitted in all directions; In rainy days, walk towards the light in the dark, and the backlight should be in a bright place because of the specular reflection of accumulated water and the diffuse reflection of the ground. The film screen is rough, and when the blackboard is rough, the light is diffused everywhere, and the "reflection" on the blackboard is specular reflection. )

Five, plane mirror imaging

1, the characteristics of plane mirror imaging: Like a virtual image, the image and the object are symmetrical about the mirror surface (the image and the object are equal in size, the connecting line between the corresponding points of the image and the object is perpendicular to the mirror surface, and the distance to the mirror surface is equal; The image is the same as the object up and down, but the left and right are opposite (Byakki Smoker's left hand is a person's right hand, and the time to look at the clock in the mirror depends on the reverse side of the paper. When the object is far away from the mirror and near the mirror, the size of the mirror remains the same, but for people who are at the same distance from the mirror and near the mirror, the size of the mirror is twice the distance).

2. Reasons for the formation of reflection in water: A calm water surface is like a flat mirror, which can be imaged (moon in water, flowers in the mirror); For each point of a physical object, the distance between the image point and the object point in the water is equal. Trees and houses are at different distances from the water. The closer the point is to the water surface, the closer the image is to the water surface. An image composed of countless points is a reflection on the water. How high an object is from the water surface is how far it is from the water surface, regardless of the water depth.

3. The reason why the plane mirror becomes a virtual image: the reflected light of the light emitted by the object on the plane mirror will not converge, and the other is divergent. The image formed by the intersection of the reverse extension lines of these rays (dotted lines when drawing) cannot be presented on the screen, and can only be observed by human eyes, so it is called a virtual image (not formed by the convergence of actual rays).

Note: The light entering the eyes does not come from the image point, but is reflected light. It is required to make light path diagrams (objects, images, reflected light and incident light) by using the plane mirror imaging law (images and objects are symmetrical about the mirror surface) and the plane mirror imaging principle (after light from the same object point is reflected, the reverse extension line of the reflected light passes through the image point);

Six, convex mirror and concave mirror.

1, the outer surface of the ball is called convex mirror, and the inner surface of the ball is called concave mirror;

2. The convex mirror has a divergent effect on light, which can increase the field of vision (rearview mirror on the car); Concave mirror can converge light (solar cooker, using reversible light path as flashlight).

Seven, the refraction of light

1. When light obliquely enters another medium from one medium, the propagation direction is deflected.

2. Light propagates in the same medium. When the medium is uneven, the propagation direction of light will also change.

3. Refraction angle: the angle between the refracted light and the normal.

Eight, the law of refraction of light

1, in the refraction of light, three lines * * * plane, the normal is in the middle.

2. When light obliquely enters water or other media from the air, the refracted light deflects to the normal direction; When light enters the air obliquely from water or other media, the refracted light is far away from the normal (it is required to draw the optical path diagram of refracted light and incident light).

3. When shooting sideways, the angle in the air is always large; At normal incidence, the refraction angle and incident angle are equal to 0, and the propagation direction of light remains unchanged.

4. The refraction angle increases with the increase of incident angle.

5. When light touches the interface between two media, reflection and refraction occur simultaneously.

6. The optical path is reversible in the refraction of light.

9. Refraction of light and its application

1. Examples related to the refraction of light in life: the position of fish in the water looks higher than the actual position (the fish is actually below and behind the position); Due to the refraction of light, the pool water looks shallower than it really is; People in the water look at the scenery on the shore higher than the actual position; In summer, the position of stars in the sky is higher than the actual position of stars; Looking at the pen through the thick glass, the pen holder seems to be in the wrong position; Chopsticks are placed obliquely in the water, as if they are bent upward; (Optical diagram required)

2. People use the refraction of light to see that the image of an object in water is a virtual image (the intersection of the opposite extension lines of refracted light).

X. light scattering:

1. After sunlight passes through the prism, it is decomposed into seven colors: red, orange, yellow-green, blue, indigo and purple. This phenomenon is called dispersion.

2. White light is polychromatic light mixed with various colors;

3. The rainbow on the horizon is the dispersion phenomenon of light;

4. The three primary colors of color light are: red, green and blue; Other colors can be mixed with these three colors, and white light can be mixed with red, green and blue. There is no black light in the world; The three primary colors of pigment are magenta, cyan and yellow, and the mixture of the three primary colors is black;

5. The color of transparent body is determined by the color light it passes through (what color passes through what color light); No, the color of transparent body is determined by the color light it reflects (what color reflects what color light, absorbs other colors, white objects emit all colors of light, and black absorbs all colors of light).

Example: A piece of white paper is painted with a red horse, green grass, red flowers and black stones. Now, when you look at this painting in a dark room with green light, you will see a black horse, a black stone and a black flower on green paper, but you can't see the grass (grass and paper are both green).

Eleven, invisible light:

1, solar spectrum: the seven colors of red, orange, yellow, green, blue, indigo and purple are arranged in sequence, which is the solar spectrum;

(From left to right, its wavelength gradually decreases; Scattering gradually increases; The sun is red at night, blue on sunny days, and the fog lights of cars are yellow.

2, infrared: infrared is located outside the red light, invisible to the human eye;

(1) All objects can emit infrared rays, and the higher the temperature, the more infrared rays are radiated; (Night vision goggles for war)

(2) The infrared ray has strong ability to penetrate clouds (remote detection)

(3) The main performance of infrared ray is its strong thermal effect; (heating)

3. ultraviolet light: it is located outside the purple light in the spectrum and is invisible to the human eye;

(1) The main feature of ultraviolet ray is its strong chemical action; (disinfection, sterilization)

(2) The physiological function of ultraviolet rays promotes the synthesis of vitamin D (children spend more time in the sun), but excessive ultraviolet rays are harmful to human body (ozone can absorb ultraviolet rays, so it is necessary to protect the ozone layer).

(3) fluorescence; (check money)

(4) Natural ultraviolet rays on the earth come from the sun, and the ozone layer prevents ultraviolet rays from entering the earth;

Chapter III Lenses and Their Applications

1. lens, transparent glass element, at least one surface is a part of the sphere (to be identified).

1, convex lens, lens with thick middle and thin side, such as hyperopia lens, camera lens, projector lens, magnifying glass, etc.

2. Concave lenses, lenses with thin edges in the middle, such as myopia lenses;

Second, the basic concept:

1, main optical axis: a straight line passing through the centers of the two spherical surfaces of the lens, expressed by CC/;

2. Optical center: always located in the geometric center of the lens; Indicated by "o"

3. Focus: The point where light rays parallel to the main optical axis of the convex lens converge on the main optical axis after passing through the convex lens is called focus; Represented by "f"

4. focal length: the distance from the focal point to the optical center (usually due to the thick lens, the distance from the focal point to the lens is about equal to the focal length). The focal length is indicated by "f". As shown in the figure below:

Note: both convex lens and concave lens have two focal points, the focal point of convex lens is the real focal point, and the focal point of concave lens is the virtual focal point;

Three kinds of special lights (to be drawn):

1. The propagation direction of light passing through the optical center remains unchanged after passing through the lens, as shown in the following figure:

2. The light parallel to the main optical axis passes through the convex lens and then passes through the focal point; After passing through the concave lens, it diverges outward, but its reverse extension line must pass through the focus (so the convex lens has a convergent effect on light, and the concave lens has a divergent effect on light), as shown in the following figure:

3. The light passing through the focal point of the convex lens is parallel to the main optical axis after passing through the convex lens; The light rays directed to the opposite focus are parallel to the main optical axis after passing through the concave lens; As shown in the figure below:

4. Roughly measure the focal length of convex lens: make the convex lens face the sunlight (sunlight is parallel light, so that the sunlight is parallel to the main optical axis of the convex lens), put a piece of white paper below, adjust the distance between the convex lens and the white paper until the light spot on the white paper is the smallest and brightest, and then measure the distance from the convex lens to the center of the light spot on the white paper with a scale, which is the focal length of the convex lens.

Five, the method of distinguishing convex lens and concave lens:

1, touch the lens by hand, the convex lens is thick in the middle and thin in the edge; The concave lens is thin in the middle and thick in the edge;

2. Let the lens face the sun, move the lens, and it is a convex lens that can get a smaller and brighter spot on the paper, otherwise it is a concave lens;

3. Look at the words with a lens, the convex lens can enlarge the words, and the concave lens can reduce the words;

6. Camera: 1. The lens is a convex lens; 2. The distance from the object to the lens (object distance) is more than twice the focal length, which is an inverted and reduced real image;

7. Projector: 1. The lens of the projector is a convex lens; 2. The function of the plane mirror of the projector is to change the propagation direction of light;

Note: In order to enlarge the image, cameras and projectors should keep the lens close to the object and away from the film and screen.

3. The distance from the object to the lens (object distance) is less than twice the focal length and more than once the focal length, which is an inverted magnified real image;

Eight, magnifying glass: 1, magnifying glass is a convex lens; 2. The distance from the magnifying glass to the object (object distance) is less than 1 times of the focal length, which is an enlarged and upright virtual image; Note: to make the object bigger, keep the magnifying glass away from the object;

Nine, explore the imaging law of convex lens: equipment: convex lens, light curtain, candle, optical bench (with scale)

X. Note: "three-center line": the flame center of the candle, the optical center of the lens and the center of the screen are on the same straight line; Also known as "three-center contour"

Eleven, convex lens imaging law (requires memorization and understanding):

Imaging Condition Object Distance (U) Imaging Attribute Image Distance (V) Application

U-2f Inverted Reduction Real Image F-V-2f Camera

U = 2f inverted, equal real image V = 2f.

F-u-2f Inverted Magnifying Real Image V-2f Projector

U = f does not image

0￠U￠F vertical magnification virtual image magnifying glass

Formula: one focus is divided into virtual reality, and the other focus is divided into size; The virtual image is on the same side and the real image is on the opposite side; Far from reality, small image, big virtual image.

Note: 1, the real image is composed of actual light, which can be displayed on the screen and can be directly seen by eyes, and all light must pass through the image point;

2. The virtual image can't be presented on the screen, but it can be seen with the eyes, and it is formed by the reverse extension line of light;

Note: concave lens is always a shrinking and upright virtual image;

Twelve, the lens of the eye is equivalent to a convex lens, and the retina is equivalent to a light screen (membrane);

Thirteen, myopia can not see the distant object clearly, the distant object is imaged in front of the retina, and the curvature of the lens is too large, so it is necessary to wear a concave lens for adjustment;

Fourteen, hyperopia eyes can't see the nearby objects clearly, and the nearby objects are imaged behind the retina, and the curvature of the lens is too small, so it is necessary to wear a convex lens for adjustment;

Microscope and telescope

Fifteen, the microscope consists of an eyepiece and an objective lens, both of which are convex lenses, which magnify the object twice;

16. The telescope consists of an eyepiece and an objective lens. The objective lens makes the object become a reduced and inverted real image, and the eyepiece is equivalent to a magnifying glass, forming an enlarged image;

Chapter IV Changes in the Situation

First, the temperature:

1, temperature: temperature is a physical quantity used to express the degree of heat and cold of an object;

Note: A hot object is considered to have a high temperature, and a cold object is considered to have a low temperature. If two objects are equally hot and cold, their temperatures are also the same. It is generally unreliable for us to judge the degree of heat and cold of an object by feeling;

2, Celsius temperature:

The common unit of (1) temperature is Celsius, which is indicated by the symbol "c";

(2) Specification of temperature in Celsius: The temperature of ice-water mixture is specified as 0℃ at one atmospheric pressure; The boiling water temperature at standard atmospheric pressure is set to100℃; Then divide the temperature between 0℃ and 100℃ into 100 equal parts, and each equal part represents 1℃.

(3) How to pronounce the temperature in Celsius: for example, "5℃" is pronounced as "5℃"; "-20 degrees Celsius" is pronounced as "20 degrees Celsius below zero" or "20 degrees Celsius below zero"

Second, the thermometer

1, commonly used thermometers are made by using the principle that liquid expands when heated and contracts when cooled;

2. Composition of thermometer: glass bulb, uniform glass tube, glass bulb assembled with appropriate amount of liquid (such as alcohol, kerosene or mercury) and scale;

3, the use of thermometer:

(1) Before use, observe the range and division value of the thermometer (how much temperature is indicated by each small scale), and estimate the temperature of the liquid. Do not exceed the range of the thermometer (otherwise it will damage the thermometer).

(2) When measuring, the glass bulb of the thermometer should be in full contact with the measured liquid, and should not be close to the wall and bottom of the container;

(3) When reading, the glass bubbles should not leave the measured liquid, and should be read after the pointer of the thermometer is stable, and the line of sight should be flush with the upper surface of the night column in the thermometer.

Third, the thermometer:

1, use: specially used for measuring human body temperature;

2. Measuring range: 35℃ ~ 42℃; The dividing value is 0.1℃;

3. You can leave your body when the thermometer reads;

4. The special structure of the thermometer: there is a very thin and curved tube (necking) between the glass bulb and the straight glass tube;

State change: the change of matter between solid, liquid and gas; Solid, liquid and gas can be transformed into each other under certain conditions. The state of existence of matter is related to the temperature of the object.

Fourth, melting and solidification: the change from solid to liquid is called melting; Changing from a liquid to a solid is called solidification.

1, the material should absorb heat when melting; Heat should be released during solidification;

2. Melting and solidification are reversible two-state processes;

3. Solids can be divided into crystalline and amorphous;

(1) crystal: a substance whose temperature (melting point) is fixed when melting; Amorphous: a substance that has no fixed temperature when it melts;

(2) The fundamental difference between crystal and amorphous is that crystal has a melting point (the temperature will absorb heat continuously when melting), while amorphous has no melting point (the temperature will absorb heat continuously when melting); (melting point: the temperature at which crystals melt);

4, crystal melting conditions:

(1) temperature reaches the melting point; (2) continue to absorb heat;

5. Conditions for crystal solidification: (1) The temperature reaches freezing point; (2) continue to release heat;

6. The melting point and freezing point of the same crystal are the same;

7, crystal melting and solidification curve:

The object in (1)AB section is solid, and its endothermic temperature rises.

(2) Point B is a solid, and when the temperature of the object reaches the melting point (50℃), it begins to melt;

(3)BC exists in stock solution and liquid, absorbs heat and keeps the temperature unchanged;

(4) Point C is liquid, the temperature is still 50℃, and the object has just melted;

(5)CD is a liquid, the object absorbs heat and the temperature rises;

(6) When 6)DE is in liquid state, the object releases heat and the temperature drops;

(7) Point E is a liquid, and when the temperature of the object reaches freezing point (50℃), it begins to solidify;

(8)EF section is solid and liquid, with constant heat release;

(9) Point F is solid, and the temperature after solidification is 50℃;

(10)FG is in a solid state, and the exothermic temperature of the object decreases;

Note: 1, the time taken for melting and solidification of materials is not necessarily the same, which is related to the specific situation;

2. Heat can only be transferred from high-temperature objects to low-temperature objects. The conditions of heat transfer are: there is a temperature difference between objects;

Verb (abbreviation for verb) vaporizes and liquefies.

1, the change from liquid to gas is called vaporization; The change of substance from gas to liquid is called liquefaction;

2. Vaporization and liquefaction are mutually reversible processes, with vaporization absorbing heat and liquefaction releasing heat;

3. Vaporization can be divided into boiling and evaporation;

(1) evaporation: a slow evaporation phenomenon, which may occur at any temperature and only occurs on the liquid surface;

Note: the evaporation speed is related to (a) the liquid temperature: the higher the temperature, the faster the evaporation (the water spilled in the room in summer dries faster than in winter; Drying clothes); (b) It is related to the surface area of the liquid. The larger the surface area, the faster the evaporation (when cooling, you should open the clothes to cool down and sweep away the accumulated water to dry quickly); (c) It is related to the air velocity on the liquid surface. The faster the air flows, the faster it evaporates (cool clothes in a ventilated place and turn on the fan to cool down in summer);

(1) Boiling: At a certain temperature (boiling point), the surface and interior of the liquid undergo intense vaporization at the same time;

Note: (a) Boiling point: The temperature at which a liquid boils is called boiling point; (b) Different liquids usually have different boiling points; (c) The boiling point of a liquid is related to pressure, and the higher the pressure, the higher the boiling point (pressure cooker cooking). (d) Conditions for liquid boiling: when the temperature reaches the boiling point, it will continue to absorb heat;

(2) The difference and connection between boiling and evaporation:

(a) They are vaporization phenomena and absorb heat; (b) Boiling only occurs at the boiling point; Evaporation can be carried out at any temperature; (c) Boiling occurs both inside and outside the liquid; Evaporation only occurs on the liquid surface; Boiling is more violent than evaporation;

(4) Evaporation can cause cooling: water is sprayed indoors in summer to cool down; People sweat to cool down; Apply alcohol to the skin to cool down when you have a fever;

(5) Different objects have different evaporation rates: for example, alcohol evaporates faster than water;

4. Liquefaction method: (1) Reduce the temperature; (2) storage and transportation of compressed volume (increasing pressure and boiling point) such as hydrogen; Liquefied gas;

Six, sublimation and sublimation

1, the direct change of matter from solid to gas is called sublimation; The direct change of a substance from a gaseous state to a solid state is called sublimation, which absorbs heat and gives off heat.

2. Sublimation phenomenon: moth balls become smaller; Drying frozen clothes; Physical state change of dry ice in artificial rainfall;

3. Sublimation: the formation of snow; Ice flowers on window glass in northern winter (on the inner surface of glass)

Formation of clouds, frost, dew, fog, rain, snow, hail and "white gas"

1 When the temperature is higher than 0℃, water vapor will liquefy into small water droplets and become dew. Adhering to dust to form fog;

2. When the temperature is lower than 0℃, water vapor condenses into frost;

3. Water vapor rises to high altitude, and when it meets cold air, it liquefies into small water droplets, forming clouds, and the big water droplets are rain; There are a lot of small ice crystals and snow (condensed by water vapor) in the clouds. Small ice crystals can melt into rain when falling, and solidify into hail when flowing with cold air at 0℃.

4. "White gas" is formed by cold liquefaction of water vapor.