Nine-year physics knowledge summary chapter XI colorful material world 1. Universe and Micro-world Universe → Galaxy → Solar System → Earth matter is composed of molecules; Molecules are particles that maintain the original properties of matter; The general size is only tens of billions of meters (0.3-0.4nm). Properties of three states of matter: solid: molecules are closely arranged, and there is a strong force between particles. Solids have a certain shape and volume. Liquid: molecules have no fixed position and move freely, and the force between particles is smaller than that of solids; Liquid has no fixed shape and fluidity. Gas: Molecules are extremely dispersed, with large spacing, and move in all directions at high speed. The interaction between particles is weak and easy to be compressed. Gas has fluidity. Molecules are composed of atoms, atoms are composed of nuclei and (extra-nuclear) electrons (similar to the solar system), and nuclei are composed of protons and neutrons. Nanotechnology: (1 nm = 10 nm), nanotechnology: (0. 1- 100 nm). The object of study is a small pile of molecules or a single atom or molecule. Second, quality: How much substance does an object contain? Mass is an attribute of the object itself, and its size has nothing to do with shape, state, position, temperature, etc. Symbol of physical quantity: meter. Units: kilograms, tons, grams and milligrams. 1t = 103kg， 1kg = 103g， 1g = 103mg。 Balance: 1, principle: lever principle. 2. Precautions: The measured object cannot exceed the weighing of the balance; Use tweezers to add and subtract weights on the plate, and the weights should not be dirty or wet; Wet objects and chemicals cannot be placed directly on the plate of the balance. 3. Usage: (1) Put the balance on a horizontal platform; (2) Put the traveling code on the ruler on the left zero line, and adjust the balance nut on the beam to balance the balance (the pointer points to the center line of the reticle or the swing amplitude is equal from left to right). (3) Put the object on the left board, put the weight on the right board, increase or decrease the weight and adjust the stroke code to balance the balance. (4) Reading: the total weight plus the scale value corresponding to the travel code. Note: In weightlessness (such as a spaceship), you can't weigh the mass with a balance. Third, density density is a special property of matter; The mass of the same substance is directly proportional to its volume, and the ratio of mass to volume is constant. Density: The mass per unit volume of a substance is called the density of this substance. Density is related to the kind and state of matter, affected by temperature, and has nothing to do with mass and volume. Formula: unit: kg/m3 g/cm3/kloc-0 /×103kg/m3 =1g/cm3. 1L = 1dm 3 = 10-3 m3； 1 ml = 1 cm3 =10-3l =10-6m3. 4. experimental principle of measuring the density of substances: experimental equipment: balance, measuring cylinder, beaker, thin-wire measuring cylinder: measuring the volume of liquid (which can indirectly measure the volume of solid), reading. Measure the density of solid (density is greater than water): Step: 1. Weigh the mass m of the solid with a balance; 2. Pour a proper amount of water into the measuring cylinder (which can immerse the object without exceeding the maximum scale) and read the volume of water (v1); 3. Tie the object with thin thread, put it into the measuring cylinder, and read out the total volume V2. Note: If the density of solid is lower than that of water, needle pressing method and drop hammer method can be used. Measure the density of liquid: Step: 1. Weigh the total mass of beaker and liquid with a balance M 1; 2. Pour the liquid in the beaker into a part of the measuring cylinder and read out the volume v2 of the liquid; 3. Weigh the mass m2 of the remaining liquid and beaker with a balance. 5. Density and social life density are the basic attributes (characteristics) of substances, and each substance has its own density. Density and temperature: temperature can change the density of matter; The thermal expansion of gas is the most significant, and its density is most affected by temperature. Solids and liquids are less affected by temperature. Abnormal expansion of water: the highest density is at 4℃; Water gets bigger when it freezes. Density application: 1, identification of substances (density measurement) 2, calculation of mass 3, calculation of volume. Chapter XII Movement and Force I. Description of Movement Movement is a common phenomenon in the universe. Mechanical motion: the change of object position is called mechanical motion. Reference: An object (or an object assumed to be stationary) selected as a standard when studying whether an object is moving or stationary is called a reference. Relativity between motion and stillness: Whether the same object is moving or still depends on the selected reference object. Second, the speed of movement: describes the speed of the object's movement, which is equal to the distance that the moving object passes in unit time. Formula: The unit of speed is: m/s; Kilometers/hour. Uniform linear motion: Uniform motion along a straight line. This is the simplest mechanical movement. Variable speed motion: the speed of motion of an object is variable. Average speed: In variable-speed movement, the speed of an object within this distance can be obtained by dividing the total distance by the time spent, which is the average speed. Third, the measurement of time and length Measurement tools for time: clocks and watches. Stopwatch (for laboratory use) Unit: s min h Length measuring tool: scale. Unit of length: m km DM cm mm μ nm The correct usage of scale: (1). Pay attention to its zero point, measuring range and dividing value before use; (2) When measuring with a scale, the scale should be along the measured length, and the worn zero line shall not be used; (3) The scribed line of the coarse scale should be close to the measured object. (4) When reading, the line of sight should be perpendicular to the ruler surface. When measuring accurately, it is necessary to estimate the next position of the dividing value. (5). The measurement result consists of numbers and units. Error: The difference between the measured value and the real value is called error. Errors are inevitable and can only be reduced as much as possible, but not eliminated. The common methods to reduce the error are: multiple measurements and averaging. Fourth, force: force is the effect of objects on objects. The forces between objects are mutual. When an object exerts a force on another object, it is also subjected to the force exerted on it by the latter. Function of force: Force can change the motion state of an object and also change its shape. The unit of force is Newton (n), 1N is about the force you use to pick up two eggs. The three elements of force are: the size, direction and action point of force; They can all affect the effect. Schematic diagram of force: the three elements of force are represented by line segments with arrows, which is called the schematic diagram of force. Fifth, Newton's first law Aristotle's point of view: the motion of an object needs force to maintain. Galileo's point of view: the motion of an object needs no force to maintain, and the motion stops because of resistance. Newton's first law: when no force acts on all objects, they always remain at rest or move in a straight line at a constant speed. Newton's first law is further deduced on the basis of empirical facts, so it can't be proved by experiments. Inertia: The property that an object keeps its state of motion unchanged is called inertia. All objects have inertia under any circumstances; The size of inertia is only related to mass. Newton's first law is also called the law of inertia. Six, two forces balance balance force: the object is in a state of static or uniform linear motion under the action of force, because the object is subjected to balance force. Balance of two forces: When an object is acted by two forces, we say that the two forces are in a state of balance if it remains stationary or moving in a straight line at a constant speed. Conditions for the balance of two forces: If two forces acting on the same object are equal in magnitude and opposite in direction, the two forces will balance each other on the same straight line. ○ (When two forces are balanced, the resultant force is zero). An object will remain stationary or move in a straight line at a constant speed when it is not subjected to force or balanced force. Chapter XIII Force and Machinery 1. Elasticity of elastic spring dynamometer: an object is deformed by force and returns to its original state when it is not stressed. This property of an object is called elasticity. Plasticity: an object cannot automatically recover its original shape after being stressed. This property of an object is called plasticity. Elastic force: the force produced by elastic deformation of an object. Spring dynamometer: principle: within the elastic limit, the greater the tension the spring receives, the greater its elongation. (Within the elastic limit, the elongation of the spring is directly proportional to the tensile force) Use of the spring dynamometer: (1) Recognize the dividing value and range; (2) check whether the pointer points to the zero scale, and if not, set it to zero; (3) Gently pull the scale hook several times to see whether the pointer returns to zero scale after each release; (4) When measuring, the force should be along the axis of the spring, and the measuring force should not exceed the scale of the spring. Second, gravity has gravity: any two objects in the universe, from celestial bodies to dust, have mutual attraction. Gravity: the force exerted by the gravity of the earth on an object. 1, the magnitude of gravity is called weight, and the gravity of an object is directly proportional to its mass. G = mg.2 Gravity direction: vertically downward (pointing to the center of the earth). 3. Gravity point (center of gravity): The earth attracts every part of the object, but for the whole object, gravity seems to act on a point, which is called the center of gravity. The center of gravity of an object with regular shape and uniform texture is at its geometric center. Friction: When two objects in contact with each other make relative motion (or tend to make relative motion), a force will be generated at the contact surface to hinder relative motion. This force is called friction. Friction direction: opposite to the direction of relative motion of objects. The factors that determine friction (sliding friction) are: experimental principle: two-force balance 1, pressure (the greater the pressure, the greater the friction); 2. Roughness of the contact surface (the rougher the contact surface, the greater the friction). Classification of friction force: 1, static friction force: there is a trend of relative motion, but there is no relative motion. 2. Dynamic friction: (1) Sliding friction: the friction generated when an object slides on the surface of another object; (2) Rolling friction: the friction generated when a wheel-shaped or spherical object rolls. Generally, rolling friction is less than sliding friction. Methods to increase friction: make the contact surface rough and increase the pressure. Methods to reduce harmful friction: (1) make the contact surface smooth; (2) reduce the pressure; (3) Rolling instead of sliding; (4) Separate the contact surface (add lubricating oil to form an air cushion). Lever lever: A hard stick can rotate around a fixed point under the action of force. This hard stick is called a lever. Five elements of lever: 1, fulcrum: the point around which the lever rotates; 2. Power: the force acting on the lever to make it rotate; 3. Resistance: the force acting on the lever to hinder the rotation of the lever; 4. Arm of force: the distance from the fulcrum to the line of action of force; 5. Resistance arm: the distance from the fulcrum to the action line of resistance. Lever balance condition: F 1l 1=F2l2. Three-bar bar: (1) labor-saving bar: l1> L2, f1< equilibrium sink; (2)& lt； Floating; (3) = Pause. Archimedes principle: the buoyancy of an object immersed in a liquid is equal to the gravity of the liquid it displaces. (The buoyancy of an object immersed in a gas is equal to the gravity of the gas it displaces) Archimedes principle formula: The methods for calculating buoyancy are: (1) Weighing method: F float =G-F, (G is the gravity of the object, F is the reading of the spring balance when the object is immersed in liquid) (2) Pressure difference method: F float =F up -F down (3) Archimedes principle:. Displacement: the quality of boiled water discharged when the ship is fully loaded according to the design requirements. Displacement = total mass of the ship (2) Submarine: ups and downs are achieved by changing its own gravity. (3) Balloons and airships: filled with gas with density less than air. (4) Densitometer: an instrument for measuring the density of liquid. The working condition is that the object floats on the liquid surface (F float =G), and the scale value is small up and big down. Chapter 15 Work and mechanical energy 1. Two necessary factors for work: the force acting on the object and the distance the object moves in the direction of the force; Calculation of work: the product of the force and the distance the object moves in the direction of the force. W=FS. Unit: Joule (J) 1J= 1Nm Working principle: When using machinery, people will do no less work than when not using machinery. That is: it is not labor-saving to use any machinery. Second, the mechanical efficiency is useful: in order to achieve people's goals and be useful to people, no matter what method is adopted, it must be done. Extra work: work that is useless to people and has to be done (usually to overcome the gravity of machinery and friction between parts). Total work: the sum of useful work and extra work. Calculation formula: η=W Useful /W Total mechanical efficiency is less than1; Because useful work is always less than total work. Third, power power (P): The work (W) completed in unit time (T) is called power. Calculation formula:. Unit: P→ watt (w) Derived formula: P=Fv. (The unit of speed should be m) Fourth, kinetic energy and potential energy: If an object can do work, it has energy (energy). The more work you can do, the more energy you have. Kinetic energy: The energy possessed by an object due to its motion is called kinetic energy. The greater the speed of an object with the same mass, the greater its kinetic energy; The greater the mass of an object moving at the same speed, the greater its kinetic energy; Among them, velocity has a great influence on the kinetic energy of objects. Attention: limit the speed to prevent excessive kinetic energy. Potential energy: gravitational potential energy and elastic potential energy are collectively called potential energy. Gravity potential energy: the energy that an object has when it is lifted. The higher the height of an object with the same mass, the greater the gravitational potential energy; The greater the mass of an object at the same height, the greater the gravitational potential energy. Elastic potential energy: the energy possessed by an object due to elastic deformation. The greater the elastic deformation of an object, the greater its elastic potential energy. 5. Mechanical energy and its transformation into mechanical energy: kinetic energy and potential energy. (Mechanical energy = kinetic energy+potential energy) The unit is: j Kinetic energy and potential energy can be transformed into each other. The ways are as follows: kinetic energy and gravitational potential energy can be transformed into each other; Kinetic energy and elastic potential energy can be transformed into each other. Conservation of mechanical energy: only kinetic energy and potential energy are transformed into each other, and the sum of mechanical energy remains unchanged. The artificial earth satellite rotates around the earth, and the mechanical energy is conserved; Perigee has the largest kinetic energy and the smallest gravitational potential energy; The apogee has the largest gravitational potential energy and the smallest kinetic energy. When perigee moves to apogee, kinetic energy is converted into gravitational potential energy. Chapter 16 Heat and Energy I. Molecular thermal motion The content of molecular motion theory is: (1) Matter is composed of molecules; (2) The molecules of all objects do random motion endlessly. (3) There is attraction and repulsion between molecules. Diffusion: the phenomenon that different substances contact and enter each other. Diffusion phenomenon shows that the molecules of all substances are constantly moving irregularly. Thermal motion: the motion of molecules is related to temperature, and the random motion of molecules is called thermal motion. The higher the temperature, the more intense the thermal motion of molecules. Intermolecular force: there is attraction between molecules; Gravity keeps solids and liquids at a certain volume. There is repulsion between molecules, which makes it difficult for solids and liquids with close molecules to be further compressed. When solids and liquids are compressed, the repulsion between molecules is greater than gravity. Solids are difficult to elongate because the attraction between molecules is greater than the repulsion. Second, internal energy: the sum of kinetic energy and molecular potential energy of all molecules in an object is called internal energy. The internal energy of an object is related to temperature and mass: the higher the temperature of the object, the faster the molecular movement and the greater the internal energy. All objects have internal energy under any circumstances. There are two ways to change the internal energy of an object: doing work and heat transfer, which is equivalent to changing the internal energy of an object. 1, heat transfer: when objects with different temperatures touch each other, the temperature of low-temperature objects increases and the temperature of high-temperature objects decreases. This process is called heat transfer. During heat transfer, the internal energy of high-temperature objects decreases and that of low-temperature objects increases. Heat: In the process of heat transfer, the amount of internal energy transferred is called heat (it is wrong to say how much heat an object contains). Unit: J.2. Doing work: (1) Doing work on an object will increase the internal energy of the object; When an object does external work, its internal energy will decrease. Greenhouse effect: the sun radiates energy to the surface of the earth, and when the earth is heated, it will also produce radiation and transfer heat to the outside. Carbon dioxide in the atmosphere hinders this radiation, and the temperature of the earth's surface will remain at a relatively stable level, which is the greenhouse effect. The extensive use of fossil fuels and deforestation have aggravated the greenhouse effect. The unit of all energy is joule. 3. Specific heat capacity Specific heat capacity (C): The temperature of a substance per unit mass increases (or decreases) by 65,438 0℃, and the heat absorbed (or released) is called the specific heat of the substance. Specific heat capacity is a property of matter, which does not change with the change of volume, mass, shape, position and temperature of matter. As long as the types and states of substances are the same, the specific heat is the same. The unit of specific heat capacity is J/(kg? C), pronounced Joule per kilogram Celsius. The specific heat capacity of water is: C=4.2× 103J/(kg? C), that is to say, when the temperature increases (or decreases) 1℃, the heat absorbed (or released) per kilogram of water is 4.2× 103 joules. Calculation of heat: ①Q- absorption = cm(t-t0)= cm△t- liter (Q- absorption is the absorption of heat, and the unit is J; C is the specific heat capacity of the object in J/(kg? ℃); M is mass; T0 is the initial temperature; T is the late temperature. ② Q discharge =cm(t0-t)=cm△t decreased by 4. Principle of heat engine: Fuel combustion converts the chemical energy of fuel into internal energy, which can do work and then into mechanical energy. Internal combustion engine: fuel burns in the cylinder, producing high-temperature and high-pressure gas, which pushes the piston to do work. Common internal combustion engines: gasoline engines and diesel engines. Four strokes of internal combustion engine: 1, intake stroke; 2, compression stroke (mechanical energy into internal energy); 3. The internal energy in the power stroke can be converted into mechanical energy); 4. Exhaust stroke. Calorific value (Q): 1kg The heat released by complete combustion of a certain fuel is called combustion calorific value. The unit is Joule/kg or Joule/m3. Calculation of heat released by fuel combustion: Q = QM calorific value is a special property of matter. The efficiency of a heat engine is called the ratio of the energy of doing work to the energy released by complete combustion of fuel. Heat engine efficiency is an important index of heat engine performance. Among all kinds of losses of heat engines, exhaust gas takes away the most energy. Making full use of the energy of exhaust gas is an important measure to improve the fuel utilization rate. Examples of energy transformation and conservation: under certain conditions, various forms of energy can be transformed into each other; Friction generates heat, and mechanical energy is converted into internal energy; The generator generates electricity, and the mechanical energy is converted into electrical energy; When the motor works, electric energy is converted into mechanical energy; Photosynthesis of plants, light energy is converted into chemical energy; When fuel burns, chemical energy is converted into internal energy. Law of conservation of energy: energy will neither be destroyed nor created, but will only be transformed from one form to another, or from one object to another. In the process of transformation and transfer, the total amount of energy remains unchanged. Chapter 16, energy and sustainable development. Energy family fossil energy: coal, oil and natural gas are formed after a long geological period and are called fossil energy. Primary energy: energy that can be obtained directly from nature. Secondary energy (fossil energy, hydropower, wind energy, solar energy, geothermal energy, nuclear energy, etc. ): energy that cannot be obtained directly from nature and must be obtained by consuming primary energy. (Electric energy) Biomass energy: Energy provided by living things. Non-renewable resources: (fossil energy, nuclear energy) energy that cannot be replenished from nature in a short time. Renewable resources: (water, wind, solar energy, etc. ) can be continuously supplemented in nature. Second, nuclear energy nuclear energy: the energy generated when the nucleus splits or polymerizes. Fission: bombarding a relatively large nucleus with neutrons, splitting it into two medium-sized nuclei and releasing huge energy at the same time. Applications: nuclear energy, atomic bomb. Fusion: nuclei with smaller mass will combine into new nuclei at ultra-high temperature, releasing more nuclear energy. Application: hydrogen bomb. Third, the sun-the huge "nuclear stove" The sun is a treasure house of human energy. Utilization of solar energy: 1, heated by a collector; 2. Use solar cells to generate electricity. Fourth, the energy revolution The first energy revolution: using fire and firewood as the main energy sources. The second energy revolution: mechanical power replaced human beings, from firewood to fossil energy. The third energy revolution: represented by nuclear energy. Directionality of energy transfer and energy conversion. V. Energy and sustainable development The impact of energy consumption on the environment: air pollution and the intensification of the greenhouse effect. Soil erosion and desertification. The ideal energy in the future: 1, which must be rich enough to ensure long-term use; 2. It must be cheap enough for most people to afford; 3. The technology must be mature and can be used on a large scale; 4, must be safe enough, clean, do not pollute the environment.