2. In the air of 150C, the speed of sound is 340m/s, which is related to the type and temperature of the medium.
3. Sound has three characteristics: tone, loudness and timbre;
The level of sound is called tone, and tone is related to frequency. The number of times an object vibrates within 1 s is called frequency. Frequency is a physical quantity representing the vibration speed of an object. The unit of frequency is Hz, abbreviated as Hz, and expressed by the symbol Hz.
The intensity of sound is called loudness, and loudness is related to amplitude (vibration amplitude) and also to the distance of the speaker;
(3) timbre refers to the characteristics of sound, which is related to the material and structure of the vocal body. People can use timbre to distinguish the sounds made by different objects (such as people and musical instruments). ).
4. Different tones have different wave densities; Different loudness, different amplitude; Different timbres have different waveforms.
5. Noise: From a physical point of view, the sound made by an object when it vibrates irregularly is called noise;
From the point of view of environmental protection, any noise that interferes with people's normal work, life and study, or the sound that people want to hear, is called noise. Noise levels are distinguished by decibels (dB). In order to protect hearing, the sound should not exceed 90 decibels, to ensure work and study, the sound should not exceed 70 decibels, and to protect rest and sleep, the sound should not exceed 50 decibels.
6. There are three ways to reduce noise: from the sound source; Weakening in the process of communication; Weakening in the human ear.
7. Sound can transmit information as well as energy. (I can give an example myself)
8. Echo: refers to the sound reflected by obstacles in the process of propagation.
The principle of sonar is echolocation. Radar is electromagnetic wave.
9. The frequency range of sound that most people can hear is 20Hz-20000Hz, which is called audible sound. The sound below 20 Hz is called infrasound, and the sound above 20000 Hz is called ultrasonic. Are voices that humans can't hear;
10. Ultrasonic characteristics: good directivity; Strong penetration; It is easy to obtain concentrated acoustic energy.
Applications: sonar, B-ultrasonic, speed measurement, cleaning, welding, stone crushing and metal flaw detection.
1 1. Characteristics of infrasound: long propagation distance; Less energy loss in the process of propagation.
Application: Predicting earthquakes and typhoons and monitoring nuclear explosions.
Chapter II Changes in the Situation
1. The degree of heat and cold of an object is called temperature. Regulation: Under normal circumstances, the temperature of ice-water mixture is 0℃; The temperature of boiling water at standard atmospheric pressure is 100℃.
2. Thermometer principle: The temperature is measured by the expansion of mercury, alcohol, kerosene and other liquids.
3. Commonly used thermometers include experimental thermometers, thermometers and thermometers; Measuring range of thermometer: 35℃ ~ 42℃; The dividing value is 0.1℃; Shake the thermometer a few times before using it.
4. The correct use of thermometer:
Take a look: see the range and dividing value of the thermometer clearly before use; Second discharge: the glass bulb of the thermometer should be completely immersed in the measured liquid to avoid touching the bottom and wall of the container; Third reading: immerse the glass bulb of the thermometer in the liquid to be measured, wait for a period of time, and then read after the pointer of the thermometer is stable; When reading, the glass bubble should stay in the liquid to be measured, and the line of sight should be flush with the upper surface of the liquid column in the thermometer.
5. The thermometer is not calibrated:
Thinking: The scale of thermometer is even, but the reading is not accurate. The reading in ice-water mixture is 4℃, while the reading in boiling water at standard atmospheric pressure is 96℃. When the thermometer shows 56℃, what is the actual temperature of a cup of hot water?
6. Three states of matter: solid, liquid and gas.
7. State change:
The process of changing a substance from solid to liquid is called melting; Melting requires heat. For example, ice turns into water
The process of changing a substance from a liquid state to a solid state is called solidification; Curing is exothermic. Such as changing molten iron into iron bars.
The process of changing a substance from a liquid state to a gas state is called vaporization; Vaporization requires heat absorption. Such as clothes being dried.
The process of changing a substance from a gaseous state to a liquid state is called liquefaction; Liquefaction is exothermic. Such as the formation of fog.
The process in which a substance changes directly from a solid state to a gas state is called sublimation; Sublimation requires heat absorption. For example, the sanitary ball has become smaller.
The process in which a substance changes directly from a gaseous state to a solid state is called sublimation; Condensation gives off heat. Such as frost formation.
8. Solids are divided into crystalline and amorphous; Haibo, ice, timely, crystal, salt, alum, naphthalene and various metals are all crystals; Rosin, glass, beeswax and asphalt are all amorphous;
9. The difference between crystal and amorphous: crystal has a certain melting point and freezing point, but amorphous does not; When the crystal melts, the temperature is constant, but it should absorb heat, and when it solidifies, the temperature is constant, but it should release heat; When the amorphous melts, the temperature will increase, but also absorb heat, and when it solidifies, the temperature will decrease and release heat. The melting point and freezing point of the same crystal are the same.
10. Melting and solidification images of crystal and amorphous:
℃ ℃ ℃ ℃
Min Min Min Min
Crystal melting crystal solidification amorphous melting amorphous solidification
1 1. There are two ways to vaporize: boiling and evaporation (evaporation has a cooling effect).
(1) Definition: Boiling is a violent vaporization phenomenon that occurs on the surface and inside of a liquid at a certain temperature;
Evaporation is a slow vaporization phenomenon, which only occurs on the surface of liquid at any temperature.
(2) Boiling conditions: ① reaching the boiling point; ② Continue to absorb heat (heat liquid).
(3) Boiling characteristics: When the liquid boils, it will absorb heat, but the temperature will not change.
(4) Factors affecting evaporation rate:
The speed of air flow on the liquid surface: the faster the air flow, the faster the evaporation;
Liquid temperature: the higher the temperature, the faster the evaporation;
Size of liquid surface area: The larger the surface area, the faster the evaporation.
12. There are two ways to liquefy: lowering the temperature (all gases) and compressing the volume (some gases).
13. Explain various physical changes in daily life.
Such as: (1) liquefaction: fog, dew and all kinds of "white gas";
(2) Dew condensation: frost, icing at the window and blackening of the lamp tube;
(3) Sublimation: Long-term use of bulb tungsten filament becomes thinner, sanitary ball becomes smaller, and frozen clothes become dry.
Chapter III Light Phenomenon
1. light source: an object that can emit light by itself is called a light source. There are natural light sources and artificial light sources.
Note: the moon is not a light source, but the reflected sunlight enters people's eyes.
2. Dispersion of light: Dispersion was discovered by British physicist Newton. The dispersion of light refers to the phenomenon that white light can be decomposed into red, orange, yellow, green, blue, indigo and violet light. The three primary colors of light are red, green and blue.
3. Color of the object: The color of an opaque object is determined by the colored light it reflects; The color of a transparent object is determined by the color of light passing through it.
Infrared and ultraviolet rays are invisible to human eyes. Everything radiates infrared rays and absorbs infrared rays at the same time. At night, people's body temperature is higher than that of objects in the wild, and people radiate more infrared rays. According to this principle, people have made infrared night vision devices. Sunlight is the main source of natural ultraviolet rays on the earth, and all high-temperature objects radiate ultraviolet rays. People often use ultraviolet rays to sterilize; Appropriate ultraviolet irradiation can synthesize vitamin D, which is helpful to the absorption of calcium. Ultraviolet rays can also make fluorescent substances glow. But ultraviolet rays are also very harmful, so people should pay attention to protecting the atmosphere.
5. Conditions for straight-line propagation of light: Light travels straight in the same uniform medium. The phenomena that can be explained by the propagation of light along a straight line are: the formation of shadows; Causes of solar and lunar eclipses; Small hole imaging; Laser collimation; "three points and one line"; Wait in line.
6. Light can travel in a vacuum without medium, with the fastest speed of 3× 108m/s or 3× 105Km/s, and the slowest speed of light in a solid.
7. Reflection of light:
We can see objects that don't emit light because of the reflection of light.
② Reflection can be divided into specular reflection and diffuse reflection; We see objects that don't emit light, because the specular reflection on the surface of the object is a bit "dazzling"; Due to the diffuse reflection on the surface of the object, we can see objects that do not emit light from all directions. ③ Law of light reflection: reflected light, incident light and normal line are 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.
7. The characteristics of flat mirror imaging:
(1) The image is equal to the size of the object;
② The distance between the image and the object to the front mirror is equal;
③ The straight line between the image and the object is perpendicular to the mirror;
(4) The image formed by the plane mirror is a virtual image.
Can be summarized as: upright, equal, equidistant, vertical, virtual image. Simply put, images and objects are symmetrical about a plane mirror. When drawing, you only need to make a symmetrical figure about the plane, but the object must be represented by a solid line, like a dotted line; All dotted lines are drawn behind the plane mirror)
Chapter IV Refractive Lens of Light
1. Refraction of light
Meaning: When light obliquely shoots from one medium to another, the propagation direction of light will change, which is called light refraction. (The main media are: air, water, glass, etc. )
(2) the law of refraction of light:
A, when light is obliquely incident from the air to other media, the refracted light is close to the normal, and the refraction angle is smaller than the incident angle;
B, when light obliquely enters the air from other media (such as water and glass), the refracted light is far from the normal, and the refraction angle is greater than the incident angle;
C. When light enters the interface vertically, the propagation direction of light remains unchanged. At this time, the refraction angle = incident angle = 0.
③ Common refraction phenomenon of light: when people look at the fish in the water (fish looks at the people on the shore), they actually see the virtual image of the fish (people), and the position of the fish (people) is higher than the actual position; Mirage is a phenomenon caused by light refraction; In the morning, people can see the sun below the horizon, which is due to the light refraction caused by the uneven atmosphere.
It is emphasized that both the reflection and refraction of light follow the principle of optical path reversibility.
2. A lens with a thick middle and a thin edge is called a convex lens, and a lens with a thin middle and a thick edge is called a concave lens.
① The propagation direction of light through the optical center of the lens is unchanged (along a straight line).
② The light rays parallel to the main optical axis are refracted by the convex lens and then converge to the focus. The distance from the focal point to the optical center is called the focal length (f). The length of the focal length reflects the ability of the lens to refract light. The shorter the focal length, the stronger the refractive power.
③ After the light parallel to the main optical axis is refracted by the concave lens, the reverse extension line of the refracted light passes through the focal point.
3. the law of convex lens imaging: (u: the distance from the object to the convex lens, referred to as the object distance)
(v) The distance from the image to the convex lens is called the image distance; F: focal length)
Object distance imaging
U & gt2f f<v & lt2f inverted. Simplified real image
U=2f v=2f inversion. Equal reality.
F<u & lt2f v & gt2f inverted. Enlarge the real image
U=f is not like a picture.
U<f stands upright. Enlarged virtual image
"One focus is divided into virtual reality, and the other focus is divided into size"
principle
Object distance (u)
Image formation
App application
camera
u & gt2f
Inverted and reduced real image
To make the image on the negative smaller, people should stay away from the object, so that the distance between the lens and the object (object distance) is farther; At the same time, adjust the focus ring to make the length (image distance) of the black box shorter.
u=2f
Inverted, equal-sized real images
Can be used to determine the size of the focal length
projector
slide projector
projector
f & ltu & lt2f
Inverted and enlarged real image
The function of plane mirror is to change the direction of light propagation; Slides should be inserted backwards, which means slides should be rotated 1800.
u=f
No imaging
To produce parallel light, the light source must be in focus.
amplifier
u & ltf
Vertical, enlarged virtual image
To enlarge the image, please keep the magnifying glass away from the object.
4. The difference between virtual image and real image
Real image:
A, the real image is the image of actual light convergence, and can be received by the light curtain;
B, the convex lens becomes a real image, which is upside down and opposite to the convex lens.
C. When the real image is formed: when the object distance (U) decreases, the image distance (V) increases and the image becomes larger;
When the object distance (u) increases, the image distance (v) decreases and the image becomes smaller.
Virtual image:
A, the virtual image is not an image formed by the convergence of real light, and cannot be received by the light curtain, and can only be observed with eyes.
B, convex lens into a virtual image, are upright, and on the same side of the convex lens.
C when the object distance u decreases, the image distance v decreases and the image becomes smaller.
When the object distance u increases, the image distance v increases and the image becomes larger.
The eyeball is like a camera, in which the lens acts as a convex lens.
(1) Myopia is caused by too thick lenses and too strong refractive power. Distant objects are imaged in front of the retina, and when they reach the retina, they are already blurred spots. Concave lens for correcting myopia.
② Hyperopia is because the lens is too thin and the refractive power is too weak, and distant objects are imaged behind the retina. Convex lens for correcting hyperopia
6. Glasses degree =100/f. Hyperopia (convex lens) degree is positive, and myopia (concave lens) degree is negative.
7. When observing an object with a microscope (both the objective lens and the eyepiece are convex lenses), the observed object becomes an inverted magnified real image through the objective lens, and the eyepiece magnifies this image into an upright magnified virtual image; The objective lens of Kepler telescope (both objective lens and eyepiece are convex lenses) becomes an inverted and reduced real image, and then becomes an upright and enlarged virtual image through the eyepiece.
8. People feel that the size of an object is not only related to the size of the object, but also related to people's perspective. The larger the angle of view, the greater people's feelings about objects.
Chapter V Motion of Objects
Preliminary knowledge of measurement
(1) length measurement:
1. Length unit: international unit is meter (m); Commonly used kilometers (Km), decimeters (dm), centimeters (cm),
Millimeter (mm), micron (um) and nanometer (nm); The relationship between them is:
1k m = 1000m； 1m = 10dm = 100cm = 103mm = 106um = 109nm。 .
2. Measuring tool: ruler
Before use: observe the measuring range, dividing value and zero scale line;
When in use; The scale should be parallel to the edge of the measured object; The scale line should be close to the measured edge; The zero scale line should be aligned with one end of the measured object;
When reading: the line of sight is perpendicular to the ruler surface; When reading accurately, it is necessary to estimate the next digit of the dividing value;
Record: The measurement result consists of numbers and units.
3. Error: The difference between the measured value and the real value is called error. Errors are inevitable.
Methods to reduce errors: select precision tools; Improve the measurement method; Average through multiple measurements.
4. Special measurement methods of length: accumulation method, coordinate method, substitution method, bending into a straight line, translation with tools, etc.
(2) Time measurement:
1. Time unit: international unit is seconds (s); Common minutes (min) and hours (h);
The relationship between them is: 1h=60min,1min = 60s;
2. Tools: stopwatches, clocks and watches
(3) Speed:
1. Method of comparing the speed of objects:
Same distance, comparison time (after the game, referee)
At the same time, compare the distance (during the game, the audience)
Time and distance are different. Compare the distance per unit time. (i.e. comparison speed)
2. Speed is a physical quantity representing the speed of an object;
3. Definition: The distance an object moves in unit time is called speed. It is represented by "υ".
4. Formula: ν = s/t (s stands for distance (m); T stands for time (seconds).
5. Units: meters per second (m/s) and kilometers per hour (km/h); 1 m/s = 3.6 km/h
(4) mechanical movement:
1. The change of object position is called mechanical motion;
2. The motion and stillness of an object are relative; Whether the object is moving or stationary depends on the selected reference object.
3. Uniform linear motion: refers to the uniform motion of an object along a straight line.
Variable-speed movement: refers to the movement in which the speed or direction changes; (average speed)