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general review outline of junior middle school physics (1)

acoustics

5. Everything that is making sound is vibrating, and the vibration stops, and the sound stops.

6. Sound is transmitted by medium, and the speed of sound propagation in air at 15℃ is 34m/s, so it can't be transmitted in vacuum.

Thermal

7. The object is hot and cold. Its principle is to make use of the thermal expansion and cold contraction properties of mercury, alcohol, kerosene and other liquids.

8. There are two units of temperature: one is Celsius temperature, and the other is international unit, which adopts thermodynamic temperature. The Celsius temperature is specified as follows: the temperature of ice-water mixture is set at degrees, and the boiling water at a standard atmospheric pressure is set at 1 degrees, and the temperature between degrees and 1 degrees is divided into 1 equal parts, each of which. (2) recognize its minimum scale.

1. When measuring the temperature of liquid with a thermometer, the correct methods are as follows: (1) The glass bulb of the thermometer should be completely immersed in the measured liquid; Do not touch the bottom or wall of the container; (2) Wait for a while after the glass bulb of the thermometer is immersed in the liquid to be measured, and then read after the indicator of the thermometer is stable; (3) When reading, the glass bubble should remain 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.

11. The change from solid to liquid is called melting (endothermic), and the change from liquid to solid is called solidification (exothermic).

12. Solids are divided into crystals and amorphous, and their main difference is that crystals have a certain melting point. Amorphous crystals do not.

13. The change of a substance from a liquid state to a gas state is called vaporization (endothermic), and the change of a gas state to a liquid state is called liquefaction (exothermic). There are two ways of vaporization: evaporation and boiling. The difference between boiling and evaporation is that boiling occurs at a certain temperature, which is a violent vaporization phenomenon on the surface and inside of a liquid at the same time, while evaporation occurs at any temperature. Vaporization that only occurs on the surface of liquid.

14. To speed up the evaporation of liquid, the temperature of liquid can be increased, the surface area of liquid can be increased and the air flow speed on the surface of liquid can be accelerated.

15. The temperature of liquid when it boils is called boiling point, and it only absorbs heat when it boils, and the temperature remains unchanged, sometimes because the boiling point of magazines in liquid will change appropriately. The boiling point of water is 1℃.

16. There are two ways to liquefy gas: one is to reduce the temperature, and the other is to compress the volume.

17. The change of a substance from a solid state to a gaseous state is called gasification (endothermic). Changing from a gaseous state to a liquid state is called liquefaction (exothermic).

optics

18. Light travels in a straight line in a homogeneous medium. The speed of light in vacuum (air) is 3×1 m/s. Shadows, solar eclipses and lunar eclipses can all be explained by light traveling in a straight line in a homogeneous medium.

19. The law of light reflection: reflection. (2) Images and objects are equal in size; (3) The line between the image and the object is perpendicular to the mirror surface, and (4) the image is a virtual image.

21. When light is obliquely incident from one medium to another, the propagation direction will generally change, which is called light refraction.

22. Convex lenses are also called convergent lenses, such as reading glasses. Concave lenses are also called divergent lenses. For example, a nearsighted mirror.

23. The principle of a camera is that when the distance between the convex lens and the object is more than twice the focal length, it becomes an inverted and reduced real image.

24. The principle of a slide projector and a projector is that when the distance between the object and the convex lens is between twice the focal length and once the focal length, it becomes an inverted and enlarged real image.

25. The principle of a magnifying glass and a microscope is that the distance between the object and the convex lens is less than the focal length. The principle of Toppler telescope is that the focal length of the eyepiece is small, and the focal length of the objective lens is large. The real image of the objective lens is inverted and reduced almost in focus, so that the real image is inverted and reduced, and the eyepiece is an enlarged virtual image, that is, f1+f2. Galileo telescope's eyepiece is a magnified virtual image, that is, F1-F2.

Force and motion

2. The measuring tool of the length is a scale, and the main unit is meters.

3. The change of the object's position is called mechanical motion, and the simplest mechanical motion is uniform linear motion.

4. Speed is a physical quantity indicating the speed of the object, which is equal to the distance that the moving object passes in unit time. Use the formula. The main unit of speed is meter/second.

26. The number of substances contained in an object is called mass. The international main unit of mass is kilogram, and the measuring tool is balance.

27. How to use the balance: (1) Put the balance on a horizontal platform, the measured object on the left panel and the weight on the right panel.

28. The mass per unit volume of a substance is called this substance. The calculation formula is ρ =. Density is an attribute of the substance itself, and it does not change with the shape and state of the object, nor does it change with the position of the object. A glass of water and a bucket of water are different in mass and volume, but the density is the same. 1 liter =1 decimeter 3, 1 milliliter =1 centimeter 3, 1 gram/centimeter 3=1 kilograms/meter 3.

29 Its physical meaning is: the mass of 1m 3 water is 1.× 13kg.

3. When measuring the volume with a measuring cylinder and a measuring cup, the line of sight should be level with the liquid level.

31. The effect of force: one is to change the motion state of the object, and the other is to deform the object.

32. The unit of force is Newton for short. The tool for measuring force is dynamometer, and the spring scale is commonly used in the laboratory. The working principle of the spring scale is that the elongation of the spring is directly proportional to the tension.

33. The magnitude, direction and acting point of force are called the three elements of force. The method of representing the three elements of force with a line segment with an arrow is called the graphic method of force.

34. Force is the action of objects on objects, and the forces between objects are mutual. The effect of force is ① to change the motion state of the object and ② to deform the object.

35. The force exerted on an object due to the attraction of the earth is called gravity, and the force exerted by gravity is the earth.

36. Gravity is directly proportional to mass, and the relationship between them is G=mg, where g=9.8 N/kg. The point of gravity acting on an object is called the center of gravity, and the direction of gravity is vertical downward.

37. Finding the resultant force of two forces is called two-force synthesis. If two forces are F1 and F2, the resultant force of the two forces in the same direction is F=F1+F2, and the resultant force in the opposite direction is F=F-F is large and small.

1. When no external force acts on all objects, they always maintain a static state or a state of uniform linear motion, which is Newton's first law.

2. The property that an object maintains a static state or a state of uniform linear motion is called inertia, so Newton's first law is also called inertia law. All objects have inertia.

3. Explain by inertia: ① Describe the state of the object first, ② Describe the changes that have taken place, ③. Therefore, the object should still maintain its original state.

4. The conditions for the balance of two forces are as follows: ① Two forces acting on an object, ② If they are equal in magnitude, ③ in opposite directions, and ④ acting on the same straight line, then these two forces are balanced. The resultant force of the two balanced forces is zero.

5. When two objects are in contact with each other, when they are about to move or have moved relatively, Friction is a force that hinders relative motion on the contact surface. Friction can be divided into sliding friction and rolling friction, and rolling friction is smaller than sliding friction. The sliding friction is related to both the pressure and the roughness of the contact surface. We should increase beneficial friction and reduce harmful friction.

6. The force that presses vertically on the surface of an object is called pressure. The direction of pressure is perpendicular to the surface of the object. The pressure is not necessarily equal to gravity. Only when the object is placed horizontally and there is no other force.

7. The pressure on an object per unit area is called pressure. The formula of pressure is P=. The unit of pressure is "N/m2", usually called "Pa". 1 Pa =1 N/m2, and the commonly used units are hectopascal (12 Pa), kilopascal (13 Pa) and megapascal (16 Pa). < P The pressure of different liquids is also related to the density. The instrument used to measure the pressure of liquids is called a manometer.

9. The formula p=ρgh is only applicable to liquids. The object meaning of this formula is that the pressure of liquids is only related to the density and depth of liquids, but has nothing to do with the weight, volume and shape of liquids. The "h" in the formula refers to the vertical distance from a point in a liquid to the liquid level. In addition, This formula is also applicable to regular, uniform and horizontally placed cubes, cylinders and other solids.

1. The container with an opening at the upper end and a communicating bottom is called a communication device. Its nature is that when the liquid in the communication device does not flow, the liquid level in each container is always level. Teapots and boiler water level gauges are communication devices. The ship lock works by using the principle of communication device.

11. Surrounding. The pressure of the atmosphere on the objects immersed in it is called atmospheric pressure. Torricelli first measured the value of atmospheric pressure. Eleven years later, in May 1654, otto gehrig, the mayor of Madeborg, Germany, made a famous hemispheric experiment in Madeborg, which proved the existence of atmospheric pressure.

12. Call the atmospheric pressure equal to 76mm mercury column as a standard atmospheric pressure. 1 standard atmospheric pressure ≈1.1×15 Pa (P=ρgh =13.6×13 kg/m 3×9.8 N/kg× .76 m ≈1.1×15 Pa). 1 Standard atmospheric pressure can support a water column about 1.3 meters high. It can support a kerosene column about 12.9 meters high.

13. The atmospheric pressure decreases with the increase of height. The instrument for measuring atmospheric pressure is called barometer. The boiling point of liquid is related to the atmospheric pressure. The boiling point of all liquids decreases when the atmospheric pressure decreases. When the air pressure increases, it will rise. Cooking in high mountains requires a pressure cooker.

14. Piston pumps, centrifugal pumps and pens suck in ink, all of which work by using the principle of atmospheric pressure.

15. An object immersed in a liquid is subjected to the upward and downward pressure difference, which is the buoyancy of the liquid to the object (F floating =F below-F above). This is the reason for the buoyancy. The buoyancy is always vertical. F floating g objects float; When an object is suspended or floating, there are F =G objects, but there are differences between them (V rows are different).

16. Archimedes principle: An object immersed in a liquid is subjected to upward buoyancy, and the buoyancy is equal to the gravity of the liquid it displaces. The formula is F =G row = ρ gV row of liquid. Archimedes principle is also applicable to gases. Usually, substances (such as iron) with density greater than water are made hollow. To float on the water. Ships, submarines, balloons and airships all use buoyancy.

17. A hard stick is called a lever if it can rotate around a fixed point under the action of force. Distinguish the fulcrum, power, resistance, power arm and resistance arm of the lever.

18. The balance condition of the lever is: power × power arm = resistance × resistance arm. ② The power arm is smaller than the resistance arm, that is, L1 L2. When it is balanced, F1 F2 is a laborious lever. ③ The power arm is equal to the resistance arm, that is, L1 = L2, and F1 = F2 when it is balanced, which is neither labor-saving nor laborious, and its specific application is a balance.

2. Many scales for weighing mass, such as steel scales and case scales, are made according to the lever principle.

21. There are two kinds of pulleys: crown block and moving pulleys. crown block is an equal-arm lever in essence, so crown block does not work hard. The movable pulley is essentially a lever with a power arm twice as large as the resistance arm, so the movable pulley can save half of the force, but it cannot change the direction of the force.

22. When using the pulley block, the pulley block uses several pieces of rope to hang the object, and the force used to lift the object is a fraction of the weight of the object. If the object rises "h", the pulling force moves "nh". Where "n" is the number of rope segments.

23. The work mentioned in mechanics includes two necessary factors: one is the force acting on the object, and the other is the distance that the object passes in the direction of the force. Work is equal to the product of the force and the distance that the object passes in the direction of the force. The formula is W=FS. The unit of work is coke. 1 coke =1 N m.

24. No work is saved by using any machinery. This conclusion is called the principle of work. When it is applied to an inclined plane, it is as follows: FL=Gh or F= G.

25. The work done by overcoming useful resistance is called useful work, and the work done by overcoming useless resistance is called extra work. Useful work plus extra work is equal to total work. Useful work is related to.

26. The work done in unit time is called power. The formula is P=. The unit is watts, 1 watt =1 joule/second, 1 kilowatt = 1, watts. In addition,

, p = = f v. The formula shows that when the vehicle goes uphill, the force (f) increases because the power (p) is constant. Speed (v) will be reduced.

Outline of the general review of junior high school physics (II)

Internal energy in the theory of mechanical energy molecular motion

1. An object can do work, so we say that it has energy. The energy that an object has due to motion is called kinetic energy. Kinetic energy is related to the speed and mass of the object. The greater the speed and mass of the moving object, The greater the kinetic energy, all moving objects have kinetic energy.

2. Potential energy can be divided into gravitational potential energy and elastic potential energy. The energy of an lifted object is called gravitational potential energy. The greater the mass of the object, the higher it is lifted, the greater the gravitational potential energy. The energy of an elastically deformed object is called elastic potential energy. The greater the elastic deformation of the object, The greater the elastic potential energy it has.

3. Kinetic energy and potential energy are collectively referred to as mechanical energy. The units of energy, work and heat are Joules. Kinetic energy and potential energy can be transformed into each other. Basic knowledge of molecular motion theory: ① substances are composed of molecules, and the molecules are extremely tiny. ② molecules do endless irregular motion. ③ There are interactive attraction and repulsion between molecules. < P