Summary of physics review two days ago
First, measure the length.
As shown in figure 1, the measured length
Length measurement is the basic measurement method, and the most commonly used tool is the scale.
As shown in Figure 2, the unit of length and its conversion
The international unit of length is meter (m), and commonly used units are kilometer (km), decimeter (DM), centimeter (cm), millimeter (mm), micron (micron) and nanometer (nm).
1km 103m 10m 10DM 10cm 10mm 103um 103nm。
Length unit conversion, small unit, large unit, large unit and small unit use, except multiplication.
As shown in Figure 3, the scale of the right to use
(1) observed value divided by zero scale line, range,
(2) to
(1) Align the ruler under the measured object along the length edge of the measuring ruler. It must be aligned and overlapped, and it is not allowed to be skewed.
Wear (2) the unused zero scale line. If the zero scale line is worn, replace it with other zero scale lines, and don't forget to subtract the zero scale value from the last reading.
(3) The thick ruler is vertical.
(4) When reading, the line of sight should be perpendicular to the surface and the ruler.
4. Accurate recording of measured values
Determination results of numbers and units
The record with the meaning of (1) has no unit, only numbers are written.
(2) Reading, reading the index estimation of the scale value.
5. Error
The difference between the measured value and the true value
Errors are inevitable, so as to minimize them and avoid things that should not happen.
Error: the average addition of multiple measured values, the selection of precision instruments and the basic reduction method can improve the measurement method and reduce the error.
6. Special measurement methods
(1) accumulation method
If the measured diameter of the thin metal wire or sheet is the measured thickness of paper, and so on.
(2) French calipers
(3), not a method
Second, simple exercise.
As shown in figure 1
The change of the position of an object is called mechanical motion.
All objects are in motion, but absolutely fixed objects are not, that is to say, motion is absolute. We usually say that motion and static phase move to another object (reference), so the description of motion is relative.
2. Reference
The study of mechanical motion is chosen as a standard object called a reference object.
(1) The reference object is an object that is stationary relative to the ground. Just choose which object as the reference, and we assume that the object is stationary.
The reference object describing the same moving object (2) can be selected arbitrarily, but it can be different from the selected reference point.
3, relatively fixed
Two objects with the same speed, moving in the same direction, or in the same position between them, are relatively static.
4 uniform linear motion
When the pace is constant and the route is linear, it is called uniform linear motion.
Uniform linear motion is the simplest mechanical motion.
5 speed
The velocity of (1) is a physical quantity indicating the velocity of an object.
(2) In uniform linear motion, speed is the distance traveled by a moving object in unit time equal to
(3) speed? Formula: V = S T
(4) the unit of speed
International unit: m/s Ordinary unit: km/h1m/s = 3.6 km/h.
6. Average speed
The movement transfer distance of an object is compared with the time it takes, which is called the average speed of the object in this journey.
The required horizontal speed must specify the driving time and average speed.
As shown in Figure 7, the measured average vehicle speed
Principle: V = S/T
Calibration of measurement management tools, stopwatches (or other timers)
Third, the sound phenomenon.
1, sound generation
The object that stops all sounds is vibrating, vibrating, and the sound will stop.
Sound is caused by object vibration, but there is no problem between sound vibration.
2. The spread of sound
Incomplete propagation of vacuum in sound propagation medium
(1) A sound medium that depends on all gases, liquids and solids is called a medium by the media. Even if astronauts on the moon talk face to face, they still need to rely on radio. This is because there is no air on the moon, and vacuum can't spread sound.
(2) the speed of sound propagation in different media
3 echo
In the process of sound propagation, the sound reflected by obstacles is called echo.
(1) The difference between echo and acoustic conditions: the echo is more than 0. 1 second before reaching the ear than the movie soundtrack.
(2) When it is less than 0. 1 sec, the reflected sound only strengthens the original sound.
(3) Using echo or healthy body, how to carry the depth away from obstacles?
four tones in classical Chinese pronunciation
The sound level is called pitch, which is determined by the generator with vibration frequency and the pitch with higher frequency.
5. Loudness
The size of sound is called loudness, which is related to the vibration amplitude and the distance from the sound source to the human ear.
6 sound
The time of sound quality emitted by different parts is called parts.
7. Noise and sources
From the physical point of view, the noise generator produces irregular chaotic vibration. From the perspective of environmental protection, anyone whose voice interferes with people's normal rest, study and work belongs to noise.
8, sound level division
According to the decibel number of sound, the level of 30 dB -40dB is an ideal quiet environment. If it exceeds 50dB, it will affect sleep, interfere with calls above 70 dB, affect work efficiency and have a long service life. If it exceeds 90dB, it will affect hearing.
9, noise reduction method
In the process of propagation, it will weaken the sound source of human ears.
Fourth, the thermal phenomenon.
1, temperature
The degree of heat and cold of an object is called temperature.
2 degrees celsius
The temperature of ice-water mixture is defined as 0 degree, and the boiling point temperature at standard atmospheric pressure is 100 degree.
3 thermometer
Principle (1): This liquid expands when heated and contracts when cooled.
(2) Structure: glass shell, capillary, glass ball, scale and liquid.
(3) Use the recognized index values within the range observed before using the thermometer.
Do the following three things with a thermometer.
(1) The thermometer is in full contact with the measured object.
② The number to be displayed, and then read it out steadily.
③ The reading is parallel to the line of sight of the liquid surface, and the thermometer is still in close contact with the measured object.
4. The main differences of public opinions on laboratory thermometers, thermometers and barometers.
Construction scale index value? What about the law?
Shrinkage above 35-42 C 0.1C ① The glass bulb of the thermometer leaves the human body for reading.
(2) and the previous rejection.
The experimental thermometer -20- 100℃ 1℃ cannot leave the analysis reading and cannot be dumped.
Thermometer -30 -50℃ 1℃ Same as above.
5, melting and solidification
The change of a substance from a solid to a liquid is called melting, which absorbs heat.
The change from liquid to solid is called solidification, the heat of solidification.
As shown in fig. 6, the melting point and freezing point
(1) solids can be divided into crystalline and amorphous.
(2) Melting point: The melting temperature of crystals is called melting point.
Freezing point: the freezing temperature of crystals, the so-called freezing point.
The melting point of the same substance is the same, so is its freezing point.
7. When a substance changes from a liquid state to a gas state, it is called vaporization. There are two different ways of vaporization: evaporation and boiling, which should be endothermic.
8, evaporation phenomenon
(1) Definition: The evaporation of liquid can occur at any temperature and only on the surface.
(2): The temperature level of liquid evaporation speed, the size of liquid surface area, and the influencing factors of air velocity on liquid surface.
9, boiling phenomenon
(1) Definition: Boiling has a strong vaporization phenomenon both inside and on the surface of the liquid.
(2) Conditions for liquid boiling: ① The temperature reaches the boiling point; ② Continue to absorb heat.
10L and condensation phenomenon
(1) A substance that changes directly from a solid state to a gas state is called sublimation, and it directly enters a solid sublimation gas.
(2) sublimation and sublimation in daily life (freezing wet clothes to dry, frost in winter)
1 1 On this day, sublimation absorbs heat and sublimation releases heat.
Fifth, the reflection of light.
1, light source: an object calls a light source that can emit light.
As shown in fig. 2, light propagates in a straight line in a uniform medium.
The atmosphere here is not uniform. When light hits the ground outside the atmosphere, it bends.
As shown in fig. 3, the speed of light
The propagation speed of light in different substances is generally different, and vacuum is the fastest.
The propagation speed of light in vacuum: C = 3× 108/s, which is close to the speed in air, 3/4C in water and 2/3C in glass.
4, the application of light along a straight line
Many optical phenomena can be explained: laser collimator, eclipse shadow, eclipse and pinhole.
5. Lighting
Lamp: a straight line indicating the direction of light propagation, that is, a straight line drawn along the direction of light propagation, and an arrow drawn on the straight line indicates the direction of light propagation (light is hypothetical, but actually does not exist).
6. Light reflection
The light guided to the interface of another medium returns to a part of the original medium, and the propagation direction of this light changes. This phenomenon is called light reflected from a medium.
7, the law of light reflection
The normal of the reflected light and the reflected light of the incident light are on the same plane; The incident rays on both sides of the normal are separated; The reflection angle is equal to the incident angle.
It can be summarized as: "Three lines on one side, two lines are separated, and the angles are equal."
Understand:
(1) reflection of incident light, and the word "prevention" is in front of the statement.
(2) Reflection condition: the in-phase axis point at the junction of two media; Result: Back to the original media.
(3) The incident angle of the reflection angle of the incident angle increases, and when the reduced incident angle is zero, the reflection angle also becomes zero.
8. Two thoughts
(1) Specular reflection: the parallel light reflected by the interface is emitted in the parallel direction, and the reflected light is only received in a certain direction.
(2) Diffuse reflection: the parallel light reflected by the interface is reflected in different directions, and the full score is acceptable reflected light, that is, all directions.
Note: the reflection law of specular reflection or diffuse reflection light
As shown in fig. 9, light reflection in the reversible optical path.
10, light of plane mirror
(1) imaging (2) changing the propagation direction of light.
As shown in figure 1 1, the imaging characteristics of the flat mirror
(1), etc. The size of the image and the object (3) standing upright as the virtual image (2) is connected with the mirror image perpendicular to the mirror and the object, and the distance between the image and the object is the same.
Understanding: The image formed by a flat mirror is based on a figure symmetrical to the mirror.
12, the difference between real image and virtual image
Real fusion, screening what the eyes see, of course, can also be like using actual light. Virtual images converge instead of actual light, but you can only see the intersection of opposite extension lines of actual light with your eyes. You can receive it without a screen.
As shown in figure 13, the application of flat mirror
(1) water ② ③ The reflection of periscope plane mirror imaging is
6. Refraction of light
1, refraction of light
Oblique light usually changes its propagation direction from one medium to another. This phenomenon is called light refraction.
Understanding: The refraction of light is the same as that of reflected light, because it occurs at the junction of two media, and only reflected light returns to the original media and is input into another media. Because the propagation speed of refracted light is different in two different substances, the change of propagation direction at the junction of two media is the refraction of light.
Note: At the junction of two media, both refraction and reflection will occur.
2, the law of refraction of light
Oblique light is sucked into water or other media from the air, and on the same plane, refracted light is separated from normal refracted light and incident light on both sides of the normal; The refraction angle is smaller than the incident angle; When the incident angle increases, the refraction angle increases. When the surface of the medium is vertically oriented, the propagation constant of light in the direction increases, and the refraction in the reversible optical path increases.
Understanding: the price of refraction law is three points: (1) three lines, (2) the separation relationship between two lines, (3) three cases of angle: ① the incident light is incident at the vertical interface, and the refraction angle is equal to 0; ② The refraction angle of light from air and water is smaller than the incident angle; (3) Light from a medium (such as water) is immersed in the air, and the incident angle of refraction immersion is greater than
As shown in fig. 3, the refraction of light in the optical path is reversible.
As shown in Figure 4, the lens and classification
Lens: A sphere made of transparent material (usually glass) with at least a part of one surface. The spherical shape of the lens has a small ratio of radius to thickness.
Category: convex lens: thick in the middle and thin in the edge.
Concave lens: thick edge and thin center.
5. Main optical axis, optical center, focal point and focal length
Principal optical axis: the straight line between the centers of two spherical surfaces.
Optical center: there is a special point on the main optical axis, and the direction of light passing through it remains unchanged. (The lens center can be considered as the optical center. )
Focusing: The biconvex lens makes the parallel light of the main axis converge to a point on the main optical axis, which is called the focusing lens, and an "F" stands for it.
Virtual focus: the point on the main optical axis where the light parallel to the main optical axis passes through different extension lines of the concave lens. This is a point that converges unreal light, so it is called virtual focus.
Focal length: The distance from the optical center of the focal point is called the focal length, which is indicated by "f".
Each lens has two focal points, the focal length and the optical center. draw
As shown in fig. 6, the action of the light of the lens
Convex lens focusing effect (Figure)
Concave lens: divergence effect of light (Figure)
7, convex lens imaging method
Distance of object
imaging
Image size
Judging from the actual situation of the location, such as
(ⅴ), should use
U & gtF
The real-world lens with U = 2f is on both sides of v = 2f.
F & ltU & lt2F。 Enlarge two lenses v & gt2f as a slide projector.
U = F imaging
ü& lt； V>ü magnifying glass on the same side of magnifying virtual image lens
I decided to memorize the laws of convex lens imaging.
I decided:
For example, smaller materials are transported downward like different sides, concentrated in two key dimensions; Homolateral active virtual image, solid
I decided:
The distance of three objects and the change of the distance of objects imaged by three boundaries;
The near real-time image of Aksa is large, but the real image of nearby objects is small.
If the object is in the current focus, erect and expand the virtual image;
Slide like a big physical focus between two focuses;
The camera shrinks slightly, and the focal length of distant objects is twice as long.
I decided:
Convex lens, technique, photography, sliding, zooming;
Jiao Wai's two real small ups and downs, the real focus is inward twice;
If this matter is focused, I like the virtual image of huge matter on the same side;
With this in mind, it's almost like a far rule.
8. If "upright" (top) is on the screen, slide back and insert.
9. The camera lens is equivalent to a convex lens, and the black box film is equivalent to a light screen. We adjust the focal length by adjusting the focus ring, but the adjustment distance is far from the lens, and the film material of the film lens should be close to the lens.
Seven. Mass and density
1, mass
(1) Definition: It refers to the quantity and quality of substances contained in an object. Represented by the letter "m"
(2) Object of quality attribute:
For a given object, determine its mass, which does not depend on the shape and position of the object.
The change of setting state and temperature.
(3) the unit of quality and transformation:
The mass of the main unit is kilograms (kg). Commonly used units are tons (t), grams (g) and milligrams (mg).
1 ton103kg103g103mg.
As shown in fig. 2, the quality metric
The quality of life scale of tools says that in physics laboratory, the balance of quality includes tray scale and physiological balance.
(1) Balance method used:
(1) The level of assets and liabilities is on the stage, and the left side of the scale is a straight line.
② Adjust the pointer of the balance nut at the right end of the rear cross beam to the center line of the indexing plate, and then balance the cross beam.
(3) Quality analysis and estimation: reduce the weight of the left side plate and the right side plate of the tweezers, and adjust the position and size of the driver until the beam is balanced.
(2) Consideration of using balance:
(1) after the balance, about two operators can't swap, or readjust the beam balance.
② The mass of the measured object cannot exceed the maximum capacity.
(3) handle with care heavy objects, don't use hands and tweezers, so as to avoid heavy hand sweat corrosion.
④ Keep the balance plate dry and clean. Don't put it directly on wet or corrosive objects.
(3) Balance between weighing and sense of quantity:
The known weight of each asset and liability quality is also called weight.
The minimum mass in the sense of balance of measurable quantity is the number of masses represented by the minimum scale.
3. Density
Density is a property of matter.
(1) Definition: The mass per unit volume of a substance is called density. Represents the letter ρ.
(2) Density formula:
(3) Unit: international unit kg/m3. The commonly used experimental device G/CM3 is 1g/cm3 = 103kg/m3.
Bali Island
As shown in figure 1, the definition of force
(1) definition: force object object
(2) Description: The definition of "role" is the abstraction of specific actions such as pushing, pulling, lifting, hanging and pressing.
2. The concept of comprehension
(1) To generate force, there must be two (or more) objects, that is, objects will not play a powerful role.
(2) When an object is stressed, there must be another object. The applied force, the force object is called the force object, and the required object is called the offset object. Therefore, there is no force or a force object without force.
In (3), the mutual contact between objects is not necessarily a force, and there is no contact between objects, and there is not necessarily no force. It is used to judge whether objects touch.
(4) The forces between objects are interactive.
(1) The object of force and the object of force always produce and disappear at the same time.
(2) Make the object of the object relative to the object, force the object to change, and study the change of the object.
As shown in Figure 3, the function of force-thus determines whether there is strong force.
(1) can be changed. These changes include the change of motion state and the change of moving speed in the moving direction.
(2) The shape and size of the object can be changed.
4. Units of force
In the international system of units, the unit of force is the size of Newton's force symbol N. 1N, such as a cow. Pick up two eggs.
5. Force measurement
(1) Tool: dynamometer laboratory dynamometer spring scale
(2) Spring balance principle: the spring tension is large and the spring stretches.
6, the correct use of spring scale
(1) Observe the range of the spring scale, and the scale and pointer of the value point to the zero line.
(2) Reading sight, pointer and scale line are on the same horizontal plane.
As shown in fig. 7, the three elements of force
When the size, direction and action point of the three elements of force are called, the effect will be affected.
Force icon: The line segments with arrows represent the three elements of force.
Force icon graphics
(1) Stretch object: square or rectangle. Spherical cyclability represents theory.
(2) Determined point of action: stippling the stressed object, the object on which the contact surface of the stressed object is the same, for example, the offset midpoint does not contact with the force applying object, or stippling the place where two or more forces act on the geometric center of the body.
(3) Newton's number is represented by a line segment one centimeter long.
(4) Video segment: the action point of the force, which is scaled along the direction of drawing a straight line according to the force, to indicate the magnitude of the force.
Draw an arrow at the end of the line segment in the direction of force (5) to indicate the direction of force.
(6) "Indicate the symbols and values of the force with arrows.
Mechanical diagram of 10
In some cases, as long as the force required by the object can be described qualitatively and the output force cannot be accurately expressed, the schematic diagram can be obtained.
1 1, the concept of gravity
(1) Definition: Objects close to the ground are subjected to gravity.
(2) Understanding: ① The gravity of an object is the earth, and its dynamic object is all objects on the ground nearby. ② The magnitude of gravity and the mass of the object.
12, three elements of gravity
(1) size: G = mg
(2) direction: always vertically downward (vertical and horizontal direction)
(3) Action point: the action of the center of gravity of the central object. Where the regular shape is the center of gravity of an object with a uniform mass distribution in its geometric center.
13, the concept of resultant force
(1) together, if the generated force acts on two forces, the force with the same effect is called force.
(2) Understanding: ① The concept of cooperation is based on the "equivalent" force, which jointly replaces the distance and the force acting on the object. It is only used to say that it is the action of two forces, so don't mistake it for an object and a force. (2) the conditions for the synthesis of two forces, these two forces must take action at the same time, otherwise it is meaningless to seek strength.
Composite material 14, force
The combination of the magnitude and direction of several known forces is called demand force.
(1) When two forces are in the same direction, the magnitude of the force is equal to the sum of the two forces; The same direction and the direction of two forces.
Mathematical formula: F CO = F 1+F2.
(2) Under the action of two forces in opposite directions, the force obtained is equal to the difference between the two forces, and the direction of the larger force.
Mathematical formula: F-F2 = F 1 (where: f1> F2)