初三知识点

初三知识点 The eleventh chapter is knowledge of quality and density 1. quality (m): the quality of matter contained in an object is called mass. 2. quality international unit: kg. Others are: tons, grams, Mg, 1 tons, =103 kg, =106 grams, =109 Mg (feed rate is 1000 Jin) 3. the mass of an object does not change with shape, state, position, and temperature. 4. quality measurement tools: laboratory balances commonly used to measure quality. The commonly used scales are trays, balances, and physical scales. The correct use of 5. scales: (1) the balance on the level of Taiwan, the tour on the left side of the zero line scale; (2) adjust the balance of the nut, the pointer refers to the midline of the dividing disk, then the balance; (3) placing the object on the left and right wheel and tweezers weight and adjust the rider on the ruler's position, until the restoration of balance beam; (4) when the mass of an object is equal to the total weight and quality right after the upstream code scale value. 6., use the balance should pay attention to: (1) can not exceed the maximum weighing; (2) add and subtract weights should use tweezers, and the action should be light; (3) do not wet objects and chemicals directly on the tray. 7. density: the mass per unit volume of a substance is called the density of such a substance. The same density, m quality, V said the volume density of the unit is kg / M 3 (also: g / cm 3), 1 g / cm 3=1000 kg / M 3; the quality of M units: kg; volume V unit is 3 meters. 8. density is a characteristic of matter, and the density of different species is usually different. 9. water density =1.0 x 103 kg / M 3 Application of 10. density knowledge: (1): identification of material balance and quality of M measured using a measured volume of V can be calculated according to the formula: material density. Re check density table. (2) quality: m= P V. (3) seeking volume: 11. the physical properties of matter include states, hardness, density, specific heat, transmittance, heat conductivity, conductivity, magnetism, elasticity, etc.. The twelfth chapter is the motion of objects 1. length measurement is the most basic measurement, the most commonly used tool is the scale. 2. the length of the main unit is meters, with symbols: m means, we walk two steps distance is about 1 meters, the height of the desk is about 0.75 meters. 3. kilometers, the unit of length and decimeter and centimeter and millimeter, micron, their relationship is: 1 km =1000 m =103 m =0.1 m =10-1 m; 1. 1 cm =0.01 m =10-2 M. 1 mm =0.001 M. =10-3 M. 1 meters =106 microns; 1 micron =10-6 meters. Correct use of scale 4: (1). To observe the zero line, its range and the minimum scale value before use; (2). With the scale measurement, measured along the length scale, not the use of zero line wear; (3). Readings when the line of sight to the vertical and the ruler, in precise measurement, to estimate read the next minimum scale value; (4). Measurement results consist of the number and the unit. 5. error: the difference between measured and true values is called error. The error is unavoidable. It can only be minimized and eliminated. The commonly used method of reducing errors is to measure the mean value by multiple measurements. 6. special measurement methods: (1) the cumulative Law: the small size objects accumulate together number can be used to measure the scale, and then measure its total length, and then divided by the number of these small objects, you can draw a small object's length. Such as measuring the diameter of a thin copper wire, measuring the thickness of a piece of paper. (2) translation: the method is as follows: (a) measuring the diameter of the coin; (b) measuring the diameter of the table tennis; (3) substitution method: some objects are not convenient to measure directly with a scale, so they can be replaced by other objects. If (a) how to measure the height of a teaching building with a short scale, please name two methods (b) how do you measure the distance from your school to your home? (c) how do you measure the length of a curve on the map? Please write out the answers to the three questions (4) estimation: the method of estimating the length of an object by visual means. 7. mechanical movement: the change of position of the object is called mechanical movement. 8.. Reference: the object that is chosen as a standard (or assumed to be immovable) when studying object motion or stillness is called a reference 9. relativity between motion and stillness: whether the same object is moving or stationary depends on the chosen reference. 10. uniform linear motion: the speed is constant, the line is straight motion. This is the simplest mechanical movement. 11. speed: the physical quantity used to indicate the speed at which an object moves. The distance traveled by a 12. speed body in unit time. Formula: s=vt The unit of speed is: M / S; km / h. 1 meters per second =3.6 km / h 13. variable speed motion: the velocity of the object is a variable motion. 14. average speed: in a variable speed movement, the total distance is divided by the time taken to get the speed of the object in this distance, which is the mean speed. By formula: everyday speed, in most cases, mean speed. 15. according to the distance: and time: 16. human invention: timing tool, hourglass, sundial quartz clock, atomic clock, clock. The thirteenth chapter, from particles to the universe 1. molecular kinetic theory are as follows: (1) substance composed of molecules, the intermolecular gaps; (2) all objects are never cease to do without regular exercise; (3) the interaction between the attraction and repulsion between molecules. 2. diffusion: different substances come into contact with each other and enter each other's phenomena. 3. when a solid or liquid is compressed, the repulsion between molecules is greater than that of gravity. Solids are difficult to elongate and are molecules that exhibit gravity more than repulsion. 4. molecules are made up of atoms. Atoms are made up of nuclei and outer electrons Consisting of protons and neutrons. 5. Thomson found electronic (1897); Rutherford (1919); Chadwick found the proton neutron discovered (1932); quark ideas (1961) proposed gell. The 6. accelerator is a powerful weapon in the exploration of small particles. 7., the Milky Way galaxy is a huge celestial system of stars and diffuse objects. The sun is just one of the ordinary stars. 8. of the universe is a hierarchical structure of celestial system, most scientists that the universe was born in a big bang 15 billion years ago, the explosion is whole, involving all the material and universe of time and space, the explosion caused the expansion of the universe is everywhere, the temperature should be reduced. 9. (an astronomical unit) refers to the distance of the earth to the sun. 10. (light years) refers to the distance that light travels in a vacuum for one year. The fourteenth chapter is the generalization of force knowledge 1. what is force: force is the action of an object on an object. The interaction of forces between 2. bodies is reciprocal. (when an object is exerting force on another object, it is also subjected to the latter's force on it). 3. force effect: force can change the movement of the object, but also can change the shape of the object. (a change in shape or volume of a substance is called deformation) The unit of 4. force is: Newton (abbreviation: ox), accord with N. 1 Newton is about the force you use to pick up two eggs. 5. laboratory stress measurement tools are: spring dynamometer. Principle 6.: Spring dynamometer in the elastic limit, the length of the spring and is proportional to the stress. 7. spring dynamometer usage: (1) to check whether a pointer is in the zero, if not, will be zero; (2) to the minimum scale and measurement range; (3) pull a few times, see every time let go, the pointer is returned to zero, (4) axis measurement measuring spring force spring and force in the same direction; the observation of reading, the line of sight must be vertical with the dial. (6) range cannot exceed the force measuring spring dynamometer. The three elements of the 8. force are the magnitude, direction, and point of action of forces, called the three elements of force, and they all influence the effect of force. The schematic diagram of the 9. force is to represent the force with a line segment with arrows. The concrete method of painting is: (1) use the starting point of the line segment as the point of action of the force; (2) draw a line with an arrow in the direction of the force. The direction of the arrow indicates the direction of the force; (3) if there are a few forces in the same diagram, the greater the force, the longer the line segment. Sometimes the output of force icons can also be of magnitude, 10. gravity: the forces acting on objects near the earth due to the attraction of the earth are called gravity. The direction of gravity is always vertical downward. 11. formula for the calculation of gravity: G=mg, in which the G is the ratio of gravity to mass: g=9.8 Newton / kg, and g=10 Newton / kg in rough calculation; gravity is directly proportional to mass. The 12. vertical lines are made by the principle that the direction of gravity is always vertical and downward. 13. gravity: the point of gravity on the object is called the center of gravity. 14. friction: two objects that come into contact with each other as they occur or have already undergone relative motion, The force on the contact surface creates a force that prevents relative motion. This force is called friction. 15. the magnitude of the sliding friction is related to the roughness of the contact surface and the magnitude of the pressure. The greater the pressure and the rougher the contact surface, the greater the sliding friction force. 16. increase the beneficial friction method: increase the pressure and make the contact surface more rough. To reduce harmful friction: (1) to make the contact surface smooth and reduce the pressure; (2) replace the sliding with rolling; (3) add lubricating oil; (4) use the air cushion. (5) make contact between objects (such as a magnetic levitation train). The fifteenth chapter sums up the knowledge of pressure and buoyancy 1. pressure: the force acting vertically on the surface of an object is called pressure. 2. pressure: the pressure on the unit area of an object is called pressure. 3. pressure formula: P=F/S, in the form of P units are: Pascal, referred to as: Palmer, 1 pa, =1 cattle / M 2, pressure F unit is: cattle; force area S units: M 2 Methods: 4. pressure increases (1) S constant, F =; (2) F (3): S unchanged, while F decrease, down S. The method of reducing pressure is the opposite. 5. the reason for the pressure of the liquid is that the liquid is gravity. 6. liquid pressure characteristics: (1) there is pressure on the liquid container bottom and wall (2), the internal liquid pressure in all directions; (3) the liquid pressure increases with depth at the same depth, liquid equal pressure in all directions; (4) the pressure of different liquids also have the relationship with the density. The calculation formula of 7.* liquid pressure: (P is the density of liquid, the unit is 3 kg / M; bovine g=9.8 / kg; h is the depth of the internal liquid free surface liquid to a vertical point distance, the units are in meters.) 8. according to the formula of liquid pressure, it is possible that the pressure of a liquid depends on the density and depth of the liquid, irrespective of the volume and the mass of the liquid. 9. the experiment that proved the existence of atmospheric pressure is the experiment on the hemispheres of heidelberg. The reason why the 10. atmospheric pressure is stronger is that the air is produced by the action of gravity, and the atmospheric pressure decreases with the increase of the height. 11. experiments to determine the atmospheric pressure are: Tori's experiment. 12. instruments for measuring atmospheric pressure are barometers, common barometers, mercury barometers, and liquid free barometers (metal boxes, barometers). 13. standard atmospheric pressure: atmospheric pressure equal to 760 millimeters of mercury. 1 standard atmospheric pressure =760 mmHg, =1.013 * 105 PA =10.34 m water column. 14. the relationship between boiling point and pressure: the boiling point of all liquids decreases when the pressure decreases and the pressure rises as it increases. 15. the relation between the size and velocity of a fluid: the greater the flow velocity in a fluid, the smaller the pressure; the smaller the velocity, the greater the pressure. 1. buoyancy: any object immersed in a liquid is subjected to a vertical upward force of the liquid. This force is called buoyancy. The direction of buoyancy is always upwards. (objects are also buoyant in the air) 2. conditions for the object to float (begin to submerge in a liquid) Method 1: (ratio of buoyancy to object gravity) (1) F float < G, sink; (2) F float > G, float (3) F, float = G, Levitate or float Method two: (than the density of objects and liquids) (1) F float < G, sink; (2) F float > G, float (3) F, float = G, suspension. (not floating) 3. the cause of buoyancy: an object immersed in a liquid is subjected to upward and downward pressure difference of a liquid. 4. Archimedes principle: an object immersed in a liquid is subjected to upward buoyancy, and the magnitude of buoyancy is equal to the gravity of the liquid it displaces. The buoyancy of an object immersed in a gas is equal to the gravitational force that it displaces 5. Archimedes principle formula: 6. method of calculating buoyancy: (1) weighing method: F float = G - F (G is object gravity, F is object immersed in liquid, spring balance reading) (2) pressure difference method: F float, =F upward, -F downward (3) Archimedes principle: (4) balance method: F floating =G (suitable for floating, suspension) 7. buoyancy utilization (1) ship: hollow material with density greater than water so that it can hold more water. This is the reason for making ships. (2) submarine: to achieve its ups and downs by changing its own gravity. (3) balloons and airships: gases that are less dense than air. The sixteenth chapter is the induction of force and motion knowledge 1. Newton's first law: all objects in the absence of external force, always remain stationary or uniform linear motion state. (Newton's first law is summed up by further reasoning on the basis of empirical facts, and therefore cannot be proved by experiments.). 2. inertia: the nature of an object in constant motion is called inertia. Newton's first law is also called the law of inertia. 3. the equilibrium state of an object: if the object is acted upon by several forces, if it is in a state of rest or in uniform motion, let us say these forces are balanced. When an object is in equilibrium under the action of two forces, it is called the two force balance. 4. the condition of two force equilibrium: two forces acting on the same object, if equal in magnitude, opposite in direction, and on the same line, the two forces are zero in equilibrium when the two forces are balanced. 5. objects will remain stationary or uniform in a linear motion without force or under the influence of a balanced force. The seventeenth chapter is the summary of simple mechanical and functional knowledge 1.: is a lever lever rod under force can rotate around the fixed point. 2. what is the fulcrum, power, resistance, power arm, resistance arm? (1) fulcrum: the point around which the lever rotates (o) (2) power: the force that enables the lever to rotate (F1) (3) resistance: the force that prevents the lever from turning (F2) (4) power arm: the distance from the fulcrum to the power line (L1). (5) resistance arm: the distance from the fulcrum to the line of resistance (L2) 3. lever balance conditions: power * power arm = resistance * arm of resistance or writing: F1L1=F2L2 or written. This equilibrium condition is the lever principle found by Archimedes. 4., three levers: (1) labor-saving lever: L1>L2, balance F1F2. Characterized by laborious, but provincial distance. (such as fishing sticks, hair clippers, scissors, etc.) (3) equal arm lever: L1=L2, F1=F2 when balance. It is neither labor-saving nor effortless. (e.g. balance) 5. fixed pulley features: no effort, but can change the direction of power. (essentially an arm lever) 6. moving pulley features: half force, but can not change the direction of power, it takes distance. (in essence, the power arm is two times the lever of the resistance arm) 7. pulley block: when using a pulley block, the pulley group uses several ropes to hang the object, and the force used for lifting the object is one fraction of the weight of the object. Two necessary factors of 1. work: one is the force acting on the object; the other is the distance that the object passes through the direction of force in two. 2. calculation of work: work (W) equals the product of force (F) and the distance of the object passing through the direction of force (s). (work = force = distance) The formula of 3. merit: W=Fs; unit: W to coke; F to Newton; s to M. (1 jiao =1 m M.) 4., the principle of work: the use of machinery, people do the work, are equal to the mechanical and direct use of the hands of the work done, that is, the use of any machine will not work. 5., inclined plane: FL=Gh slope length is several times higher than the slope, thrust is a fraction of the weight. (screws, winding roads are also slopes) 6.: hard work with mechanical efficiency ratio is called mechanical efficiency. Formula: P /W=. 7. power (P): the work done in unit time (T) (W) is called power. Calculation formula:. Units: P to Watt; W to coke; t to sec. (1 watts =1 Jiao / sec). 1 kW =1000 watts) In the eighteenth chapter, the knowledge of mechanical energy and internal energy is summed up 1., when an object can do work, the object has energy. 2. kinetic energy: the kinetic energy of an object due to motion. 3. the greater the speed of the moving object, the greater the mass, the greater the kinetic energy. The 4. potential energy is divided into gravitational potential energy and elastic potential energy. 5. gravitational potential energy: the energy of an object due to its height. The greater the mass of the 6. object, the higher the lift, the greater the gravitational potential energy. 7. elastic potential energy: the elastic energy of an object due to an elastic deformation. The greater the elastic deformation of a body of 8., the greater its potential energy of elasticity. 9. mechanical energy: kinetic energy and potential energy collectively. The mechanical energy = kinetic energy + potential energy unit is: Joule 10., kinetic energy and potential energy can be transformed into each other. Methods include kinetic energy, gravitational potential energy, and kinetic energy, elastic potential energy. Eleven The mechanical energy available to humans in great quantities is wind energy and water power. 1. internal energy: the sum of kinetic energy and molecular potential energy that all molecules in an object do irregular motion is called internal energy. (internal energy is also called heat energy) 2., the internal energy of an object is related to temperature: the higher the temperature of an object, the faster the molecular motion, the greater the internal energy. 3. thermal motion: irregular movements of a large number of molecules in an object. 4., there are two ways to change the internal energy of an object, namely, doing work and heat transfer. The two methods are equivalent to changing the internal energy of an object. 5. objects do external work, and the internal energy of an object decreases; The outside can do work and the internal energy of an object increases. 6. objects absorb heat, and when the temperature rises, the body can increase; An object emits heat, and when the temperature is lowered, the object can be reduced. 7. all energy units are: joule. 8. heat (Q): in the heat transfer process, the amount of energy transferred is called heat. It is wrong to say how much heat an object contains 9. specific heat (c): a substance whose mass is raised (or lowered) by 1 degrees centigrade. The heat absorbed (or released) is called the specific heat of this substance. 10. heat is a property of matter. It does not change with the volume, mass, shape, position, or temperature of matter. As long as the substance is the same, the specific heat is the same. 11., the specific heat unit is: Joule / kg (Celsius), read as: joule per kilogram celsius. The specific heat of 12. water is C=4.2 * 103 joules / kg, indicating the physical meaning of water per kilogram, when the temperature increases (or decreases) at 1 DEG C, the absorption (or release) heat is 4.2 * 103 joules. 13. calculation of heat: Q =cm (t-t0) =cm absorption t (Q absorption is the absorption of heat up, the unit is C Joule; specific heat of an object, the unit is: coke / (kg - C); m quality; t0 is the initial temperature T is the temperature later. The Q =cm (t0-t) =cm t drop 1. calorific value (q): 1 kg, a certain fuel is completely burned out of heat, called calorific value. The unit is: Joule / kg. 2., fuel combustion heat release calculation: Q put =qm; (Q put is heat, unit is: Joule; q is calorific value; unit is: coke / kg; m is quality, unit is: kg. 3., internal energy can be used to heat or work. 4. the internal combustion engine can be divided into gasoline engines and diesel engines, and their working cycle consists of four strokes: suction, compression, doing work and exhaust. A cycle of work done 1 times, the piston reciprocating 2 times, the crankshaft for 2 weeks. 5. the efficiency of a heat engine: the ratio of the energy that is used to do that part of the energy and fuel to burn out completely, which is the efficiency of a heat engine. The efficiency of a heat engine is an important index of the performance of a heat engine 6. in the heat engine's various losses, the exhaust gas takes away the energy to be most, tries to use the exhaust gas energy, is enhances the fuel utilization rate the important measure. The nineteenth chapter is the summary of energy and sustainable development One The history of human exploitation and utilization of energy: fire, fossil energy, electric energy, nuclear energy. 2. many kinds of energy, from different angles can be divided into two primary energy and energy; renewable energy and non renewable energy; conventional energy (traditional energy and new energy); clean energy and clean energy. 3., there are two ways of obtaining nuclear energy: heavy nuclear fission and light nuclear fusion (fusion, also known as thermonuclear reaction). The atomic bomb and the currently manufactured nuclear power plants use the fission of the heavy nuclei to release energy, while the hydrogen bomb uses the fusion energy of light nuclei to release energy. The major components of the 4. nuclear power plant include nuclear reactors, heat exchangers, steam turbines and generators. 5. solar energy is produced by continuous nuclear fusion. Virtually all of the earth's energy except nuclear energy, geothermal energy, and tidal energy comes from the sun. The three ways for human to utilize solar energy are: photothermal conversion (solar water heater); photoelectric conversion (solar cell); photochemical conversion (green plant). Conversion of 6. energy and law of conservation of energy is not just destroyed, not baseless, it will only change from one form to another, or from one object to another object, and in the process of conversion or transfer, the total amount of unchanged. 7., energy transfer and transformation have directionality. Useful energy output Converted energy 8. efficiency of an energy conversion device = - - - * 100% The total energy input