Calculation formula of water buoyancy V row It is the calculation formula of V row, f floating = P liquid GV row

Calculation formula of water buoyancy V row It is the calculation formula of V row, f floating = P liquid GV row

V row = f floating / P liquid G

Knowledge summary of force, lever principle, pulley and pulley block (note)
Note which I study is not good, if good, the more complete the better, as long as good I will give + points~

4、 Force: force is the action of objects on objects. The action of forces between objects is mutual. (when an object applies a force on another object, it is also subjected to the force of the latter on it at the same time). Effect of force: force can change the state of motion of an object and the shape of an object. The unit of force is Newton (n). 1n is about when you pick up

Define the operation of set a and B as a * b = {x | x ∈ A and X ∈ B}. Try to write an expression containing set operation symbols "*", "∪", "∩", which holds for any set a and B?
A question that I didn't understand at all,

When a = B, all the above conditions are satisfied

Junior high school physics series parallel circuit knowledge summary, related capacity includes: voltage, current, resistance, electric energy, electric power, electric heating knowledge
For example, in a series circuit, Q1: Q2 = R1: R2
Just a brief introduction.

Identification of series circuit and parallel circuit: series circuit: the current is not bifurcated, parallel circuit: the current is bifurcated

Who knows the English expression of Einstein's famous mass energy equation?
E = MC2 (square)

Heat energy is equivalnent to mass.We have Energy equals mass times the speed of light square.

1. Why houses (especially huts) are swept up by strong wind, and why is the pressure difference between upper and lower rather than left and right
2. Why is the velocity on the upper surface of the wing greater than that on the lower surface?
3. What is the principle of our infusion bottle and why is there a thin tube inserted there?
Please talk about physics strong brother and sister!

1. Because the pressure inside the house is strong, the air velocity on the roof is large, the pressure is small, and those with large pressure go to the place with small pressure, so the roof will be rolled up by strong wind. The pressure difference between the top and the bottom is very strong, but the pressure difference between the left and the right is not obvious. In fact, there is also a curve above the wing. The same amount of gas flows at the same time. The flow with long distance is faster, so the flow above the wing is

English translation
RT
Be correct

Einstein's mass-energy equation

Junior high school physics knowledge summary should be detailed

Summary of junior high school physics knowledge points
The first chapter summarizes the knowledge of sound phenomenon
1. Sound generation: produced by the vibration of an object. When the vibration stops, the sound stops
2. Sound transmission: sound is transmitted by medium. Vacuum cannot transmit sound. Usually, the sound we hear is transmitted by air
3. Speed of sound: in air, the speed is 340m / s. sound travels faster in solid than in liquid, and in liquid than in air
4. The distance can be measured by echo: S = 1 / 2vt
5. Three characteristics of musical sound: tone, loudness and timbre. (1) tone refers to the height of the sound, which is related to the frequency of the speaker. (2) loudness refers to the size of the sound, which is related to the amplitude of the speaker and the distance between the source and the listener
6. Ways to reduce noise: (1) at the sound source; (2) in the process of transmission; (3) at the human ear
7. Audible sound: sound wave with frequency between 20Hz and 20000hz; ultrasonic wave: sound wave with frequency higher than 20000hz; infrasound wave: sound wave with frequency lower than 20Hz
8. Ultrasonic features: good directivity, strong penetration, concentrated sound energy. Specific applications include: sonar, B-ultrasound, ultrasonic speed detector, ultrasonic cleaner, ultrasonic welder, etc
9. Characteristics of infrasound wave: it can spread far away, easily bypass obstacles, and go through all directions. Infrasound wave of a certain intensity will cause harm to human body, even damage mechanical buildings, etc. it is mainly produced in the nature of volcanic eruptions, tsunamis, earthquakes, etc. in addition, human made rocket launch, aircraft flight, Mercedes Benz of trains and cars, nuclear explosion, etc. can also produce infrasound wave
The second chapter is the knowledge induction of the change of state of matter
1. Temperature: refers to the cold and hot degree of the object. The measuring tool is thermometer, which is made according to the principle of liquid expansion and contraction
2. Centigrade temperature (℃): the unit is centigrade. The stipulation of 1 centigrade: set the temperature of ice water mixture at 0 ℃, set the temperature of boiling water at a standard atmospheric pressure at 100 ℃, divide it into 100 equal parts between 0 ℃ and 100 ℃, and each equal part is 1 ℃
3. Common thermometers are (1) laboratory thermometer; (2) thermometer; (3) thermometer
Thermometer: the measuring range is 35 ℃ to 42 ℃, and the temperature is 0.1 ℃ for each small cell
4. Use of thermometer: (1) observe its range and minimum scale value before use; (2) when using, the glass bulb of thermometer should be completely immersed in the liquid to be measured, do not touch the bottom or wall of the container; (3) read after the thermometer is stable; (4) when reading, the glass bulb should continue to stay in the liquid to be measured, and the line of sight should be level with the upper surface of the liquid column in the thermometer
5. Solid, liquid and gas are three states of matter
6. Melting: the process of material changing from solid to liquid is called melting. It needs to absorb heat
7. Solidification: the process of material changing from liquid to solid is called solidification. It needs to release heat
8. Melting point and freezing point: the constant temperature of crystal melting is called melting point; the constant temperature of crystal solidification is called freezing point. The melting point and freezing point of crystal are the same
9. Important difference between crystal and non crystal: crystal has a certain melting temperature, but non crystal has no melting point
10. Melting and solidification curves:
11. (crystal melting and solidification diagram) (amorphous melting diagram)
12. In the figure above, ad is the crystal melting curve, the crystal is in solid state in AB section, melting process in BC section, endothermic, but the temperature remains unchanged, in solid-liquid coexistence state, CD section is in liquid state; while DG is the crystal solidification curve, de section is in liquid state, EF section is the solidification process, exothermic, temperature remains unchanged, in solid-liquid coexistence state, FG is in solid state
Vaporization: the process of material changing from liquid state to gas state is called vaporization. The ways of vaporization include evaporation and boiling. Both of them should absorb heat
Evaporation: slow vaporization at any temperature and only on the surface of liquid
15. Boiling: it is a violent vaporization phenomenon that occurs at the same time inside and on the surface of the liquid at a certain temperature (boiling point). When the liquid boils, it needs to absorb heat, but the temperature remains unchanged. This temperature is called boiling point
16. The factors that affect the speed of liquid evaporation: (1) liquid temperature; (2) liquid surface area; (3) the speed of air flow above the liquid surface
17. Liquefaction: the process of a substance changing from a gaseous state to a liquid state is called liquefaction. Liquefaction requires exothermic heat. Methods to liquefy a gas include lowering the temperature and compressing the volume. (liquefaction phenomena such as white gas, fog, etc.)
18. Sublimation and Sublimation: the direct change of a substance from a solid state to a gaseous state is called sublimation, which needs heat absorption; and the direct change of a substance from a gaseous state to a solid state is called sublimation, which needs heat release
19. Water cycle: water in nature is constantly moving and changing, forming a huge water cycle system. Water cycle is accompanied by energy transfer
The third chapter summarizes the knowledge of light phenomenon
1. Light source: the object that can emit light is called light source
2. Sunlight is composed of red, orange, yellow, green, blue, indigo and purple
3. The three primary colors of light are red, green and blue; the three primary colors of pigment are red, yellow and blue
4. Invisible light includes: infrared ray and ultraviolet ray. Features: infrared ray can make the irradiated object heat, and has thermal effect (for example, the heat of the sun is transmitted to the earth by infrared ray); the most significant property of ultraviolet ray is that it can make fluorescent substances emit light, and it can also sterilize
1. Straight line propagation of light: light propagates along a straight line in a uniform medium
2. The maximum propagation velocity of light in vacuum is 3 × 108m / s, and that in air is 3 × 108m / s
3. We can see objects that don't emit light because the light reflected by these objects comes into our eyes
4. The law of light reflection: the reflected light, the incident light and the normal are in the same plane, the reflected light and the incident light are separated on both sides of the normal, and the reflection angle is equal to the incident angle. (Note: the light path is reversible)
Diffuse reflection and specular reflection follow the law of light reflection
6. The imaging characteristics of plane mirror: (1) the plane mirror forms a virtual image; (2) the size of the image is equal to that of the object; (3) the distance between the image and the object to the mirror is equal; (4) the line between the image and the object is perpendicular to the mirror. In addition, the image formed in the plane mirror is inverted from left to right with the object
7. Application of plane mirror: (1) imaging; (2) changing light path
8. Improper use of flat mirror in daily life will cause light pollution
Spherical mirror includes convex mirror (convex mirror) and concave mirror (concave mirror), both of which can image. Specific applications include: convex mirror is used for rear-view mirror of vehicle and mirror in shopping mall; concave mirror is used for reflector of flashlight, solar cooker and mirror worn on eyes by doctors
The fourth chapter summarizes the knowledge of refraction of light
Refraction of light: the phenomenon that the direction of propagation of light changes when it slants from one medium to another
Refraction law of light: light slants into water or other medium from air, and the refracted light, incident light and normal are in the same plane; refracted light and incident light are separated on both sides of normal, and the refracted angle is less than the incident angle; when the incident angle increases, the refracted angle also increases; when the light is vertically directed to the surface of medium, the propagation direction does not change. (refracted light path is also reversible)
Convex lens: a lens with thick center and thin edge. It can converge light, so it is also called convergent lens
Convex lens imaging:
(1) When the object is beyond the double focal length (U > 2f), it becomes inverted and reduced real image (image distance: F)

Does matter in the mass energy equation E = MC2 mean all matter or only nuclear matter?

It's all matter
When the positron and antimatter meet and annihilate (any substance has its corresponding antimatter), the mass energy equation is obeyed. The mass energy conversion rate is 100%, and the mass energy conversion rate of nuclear reaction is only less than 7%

Summary of important knowledge points of junior high school physics

Speed formula: v = s / T formula deformation: S = VT t = s / V average speed: v = s total / T total example: the speed V1 of the first half of the journey and the speed V2 of the second half of the journey are known, and the average speed of the whole journey is: (if the journey is 2S), then) v = s total / T total = (S1 + S2) / (T1 + T2) = 2S / (T1 + T2) = 2S / (s / V1 + S / V2) = 2v1v2 / (V1 + V