Knowledge combing:

1. Material structure

(1) The universe is made of matter, and matter is made of molecules and atoms.

(2) Matter generally exists in the form of solid, liquid and gas, and has different physical properties in different states.

(3) The center of the atom is the nucleus, which is composed of protons and neutrons, and electrons move around the nucleus.

(4) The size of the universe is usually measured in light years, and the size of atoms is usually measured in nanometers.

2. Quality

(1) The quantity of substances contained in an object is called mass, which does not change with the shape, state and position of the object.

(2) The international unit of mass is kilograms, and the mass is usually measured by a balance.

3. Density

(1) The mass per unit volume of a substance is called its density. Density is a property of matter.

(2) The formula of density: P=, and the international unit is kg/m3.

(3) An indirect measurement method of density measurement, in which the mass of the object is measured with a balance, the volume of the object is measured with a measuring cylinder, and then the calculation is made according to the formula.

Chapter XII Movement and Strength

Knowledge combing:

1. Mechanical motion

We call the change of object position mechanical motion.

2. Reference object

(1) Definition: Whether an object is moving or stationary depends on which object is the standard. An object selected as a standard is called a reference object.

(2) Whether an object is moving or static is relative to the selected reference object, that is, motion and static are relative.

3. The speed of exercise

(1) speed

① Physical meaning of speed: speed is a physical quantity representing the speed of an object.

② Formula of speed: V represents speed, S represents distance, and T represents time.

③ The main unit of speed is meters per second (m/s), and the common unit is kilometers per hour (km/h),1m/s = 3.6 km/h. ..

④ Uniform linear motion: The uniform motion of an object along a straight line is called uniform linear motion. This is the simplest mechanical movement.

(2) Average speed

① Variable speed movement: The movement speed of common objects is variable, which is called variable speed movement.

Physical meaning of average speed: roughly describe the average speed of objects with variable speed.

(3) The average speed or the speed of uniform linear motion can be calculated by the speed formula. As long as we know the two factors in the formula, we can calculate the third unknown.

4. Length

(1) The basic tool for measuring length is a ruler. Before using the scale, you should "keep three": zero scale line, range and dividing value; When using a ruler, we should pay attention to the five methods of "selecting, putting, watching, reading and recording": we should choose a ruler with an appropriate range according to the measurement requirements; Place the ruler along the measured object; When observing the instructions, the line of sight should be perpendicular to the ruler surface; In accurate measurement, it is necessary to estimate the next bit of frequency division value; The recorded measurement results consist of numbers and units.

(2) The more accurate measuring tools are vernier caliper and screw micrometer.

(3) the unit of length

① The main unit of length is meter (m). Other commonly used units are kilometer (km), decimeter (dm), centimeter (cm), millimeter (mm), micron (micron), nanometer (nm) and so on.

② unit conversion: 1 km= 103m,1m =10dm =102cm =103mm =106μ m =/kloc-.

5. Time

The basic unit of (1) time is seconds (s), and other commonly used units are hours (h) and minutes (min).

1 hour =60 minutes, 1 minute =60 seconds.

(2) The measuring tool is a clock. Stopwatches are used in sports fields and laboratories, and sundials and hourglasses are ancient timekeeping tools.

Step 6 be wrong

① Definition: The difference between the measured value and the real value is called error.

② The causes of errors are mainly related to measuring tools and people.

③ The methods to reduce the error mainly include: using precise measuring tools; When measuring the same length, the error can be reduced by choosing the average method of multiple measurements.

④ Errors and errors are different. Mistakes are not mistakes, they can only be reduced and cannot be avoided. The error is caused by non-compliance with the measurement rules, which should not happen and should be avoided.

7. Force

The unit of (1) force: Newton, abbreviated as cow, with symbol N. The force to lift an egg is about 0.5 N..

(2) The function of force: First, force can change the motion state of an object (motion state includes motion speed and motion direction); Second, force can change the shape of an object.

(3) The three elements of force: the magnitude, direction and action point of force. All three elements of force will affect the effect. (4) Schematic diagram of force: The three elements of force can be described intuitively. Force is represented by a line segment with an arrow. Generally, the starting point is on the object, that is, the stress point. The end of the line segment is marked with an arrow, indicating the direction of the force. In the same figure, the longer the line segment, the greater the force. Finally, the magnitude of the force is marked by numbers and units next to the arrow.

(5) The forces between objects are mutual. The force-applying object is also a force-applying object, and the force cannot exist independently from the object, nor can the object generate force. Powerful objects may not touch each other.

8. Newton's first law

(1) Content: All objects are always at rest or moving in a straight line at a constant speed without force.

(2) Explanation: "Always keep still or move in a straight line at a constant speed" means that when an object is not acted by a force, the original static object will remain still, and the original moving (any moving) object will always move in a straight line at the speed when the force disappears.

(3) Newton's first law is deduced on the basis of experiments.

9. inertia

(1) Definition: We call inertia the property that an object keeps its state of motion unchanged.

(2) Inertia is only related to the mass of the object. The greater the mass, the greater the inertia of the object, which has nothing to do with the speed and state of the object.

(3) Understand the inertial phenomena around you and explain them with inertial knowledge.

10. Balance of two forces

(1) The concept of two-force balance: When an object is at rest or moving in a straight line at a constant speed under the action of several forces, it is said that these forces are balanced, and then the object is in equilibrium and the resultant force is zero. If an object is in equilibrium under the action of two forces, it is called two-force equilibrium.

(2) Conditions for the balance of two forces: If the two forces acting on an object are equal in magnitude and opposite in direction, and on the same straight line, the two forces are in balance with each other.

(3) The relationship between "balance force" and "interaction force" is that they are all equal in size and opposite in direction, but the two forces of "balance force" act on the same object, while the two forces of "interaction force" act on two objects respectively.

Chapter XIII Force and Machinery

Knowledge combing:

1. elasticity

(1) Definition: The force generated by elastic deformation of an object is called elastic force.

(2) The condition of elasticity: the object is elastically deformed.

Any object will be deformed after being stressed, and some objects can be restored to their original state after being stressed. This property is called elasticity, and such deformation is called elastic deformation. There are also some objects that can't return to their original shape after removing the force. This property is called plasticity.

There is a certain limit to the elasticity of an object, beyond which it cannot be restored to its original state after the force is removed. For example, when using springs, rubber bands, etc. Their elastic limit cannot be exceeded, otherwise they will be damaged.

(3) Elastic force direction: consistent with the direction in which the object recovers elastic deformation.

2. Spring dynamometer

(1) dynamometer: The instrument for measuring force is called dynamometer. Commonly used dynamometer includes spring dynamometer, grip dynamometer and so on.

(2) Spring dynamometer

① Principle of spring dynamometer: within the elastic limit, the elongation of the spring is directly proportional to the tensile force, that is, the greater the tensile force, the greater the elongation of the spring.

② Correct use of the spring dynamometer: "two observations and one adjustment", that is, "two observations" means observing the measuring range (measuring range) first, and the force applied to the spring dynamometer cannot exceed its maximum measured value, otherwise it will damage the spring dynamometer. It is necessary to observe the graduation value of the spring dynamometer and identify how many cows each cell represents. "One adjustment" means that the pointer of the spring dynamometer is not in the zero line position before use, and the pointer should be adjusted to zero first. If you can't adjust the zero, subtract the index from the beginning to the end after reading to get the measured force.

In addition, when using the spring dynamometer, we should pay attention to the following points. Before measuring, gently pull the hook back and forth several times along the axis of the spring, then observe whether the pointer can return to its original position after being released, and check whether there is excessive friction between the pointer, the spring and the shell; Second, when measuring, the tension direction is along the spring axis to avoid excessive friction between the hook rod and the shell; Third, read after the pointer is stable. When reading, the line of sight must be perpendicular to the scale line of the pointer.

3. Gravity

(1) Gravity: There is a force of mutual attraction between any two objects in the universe, which is gravity.

(2) Gravity

Gravity is also called weight.

The gravity of an object is directly proportional to its mass. The ratio of gravity to mass is about 9.8 N/kg. If this ratio is represented by g, and gravity (unit n) and mass (unit kg) are represented by g, the relationship between gravity and mass can be written as G=mg. G=9.8 N/kg, that is to say, the gravity of an object with a mass of 1 kg is 9.8 Newton. G = 10N/kg, and accuracy is not required.

② Gravity direction: the gravity direction is always vertical downward. Can be used to make a thick vertical line, check whether the wall is vertical, and check whether the desktop is horizontal.

③ Center of gravity: The center of gravity acting on an object is called the center of gravity of the object. The center of gravity of an object with uniform texture and regular shape is its geometric center. For objects with uneven texture or irregular shape, the center of gravity can be found by supporting method or hanging method according to the principle of two-force balance. The center of gravity may or may not be on the object.

Step 4 rub

(1) Definition: When two objects are in contact with each other and make relative motion, there will be a force on the contact surface that hinders the relative motion. This force is called friction.

(2) The direction of friction: always opposite to the direction of relative motion of objects.

(3) Category: Friction is divided into static friction, sliding friction and rolling friction.

(4) Factors affecting sliding friction: The magnitude of pressure and roughness of contact surface have nothing to do with contact area, movement speed and other factors.

(5) Methods of increasing and reducing friction

Ways to increase beneficial friction: increase pressure to make the contact surface rougher; Methods to reduce harmful friction: reduce the pressure to make the contact surface smooth, and replace sliding friction with rolling friction to separate the two contact friction surfaces from each other.

5. Leverage

(1) Definition: A hard rod can rotate around a fixed point under the action of force. This hard bar is a lever.

(2) Five elements: one point two forces and two arms.

"One point" is the fulcrum, and the point around which the lever rotates is represented by "O".

"Two forces" are power and resistance, and their action points are all on the lever. Power is the force that makes the lever rotate, generally expressed as "F 1", and resistance is the force that prevents the lever from rotating, generally expressed as "F2".

The "arms of strength" are power arm and resistance arm. The distance between the power arm and the fulcrum and the power action line is generally expressed as "L 1", and the distance between the resistance arm and the fulcrum and the resistance action line is generally expressed as "L2".

(3) Lever balance conditions

When the lever is stationary or rotating at a constant speed, it is said that the lever is balanced.

The balance condition of lever: power× power arm = resistance× resistance arm, expressed as F 1L 1 =F2L2, or written as =.

(4) Three kinds of levers and their characteristics

① labor-saving lever: when the power arm >; Resistance arm, according to the lever balance condition, we can know its power.

② laborious lever: power arm time; Resistance, this lever is a laborious lever. A laborious lever is laborious, but it saves distance. Such as fishing rods, hair clippers, rowing oars, etc.

③ Equal-arm lever: when power arm = resistance arm, according to the lever balance condition, it is known that power = resistance, then this lever is equal-arm lever. Equal arm lever saves neither labor nor distance. Such as a balance.

6. Pulleys and pulley blocks

The pulley is a deformed lever.

(1) Types and characteristics of pulleys

① crown block: the shaft of the pulley does not move with the object, and this pulley is the crown block. The crown block does not save effort (F=G), but it can change the direction of force. The crown block is essentially an equal-arm lever (both the power arm and the resistance arm are the radius of the pulley).

② Moving pulley: The shaft of the pulley moves with the object, and this pulley is a moving pulley. Using movable pulleys can save manpower. When the pulley is lifted vertically without considering self-weight and friction, it can save half of the force F= G, but it cannot change the direction of the force. The moving pulley is essentially a lever, and its power arm (pulley diameter) is twice as large as the resistance arm (pulley radius).

③ Pulley block: the crown block and the movable pulley are combined into a pulley block. Using pulley block can save labor and change the direction of force. The labor-saving situation of pulley block depends on the number n of rope segments contacting the moving pulley. Without considering pulley friction, the pulling force of pulley block is F= (G +G moving pulley).

7. Other simple machines: shafts and inclined planes are labor-saving simple machines. Axles in life include door handles, steering wheels and wrenches. Panshan highway belongs to inclined plane.

Chapter XIV Pressure and Buoyancy

Knowledge combing:

1. pressure

(1) Definition: the force vertically pressing on the surface of an object.

(2) Direction: always point vertically to the surface of the pressed object.

(3) The point of action of pressure is on the pressed object.

(4) Pressure is sometimes caused by gravity, and its magnitude is related to gravity; Sometimes it is not caused by gravity, and the size has nothing to do with gravity.

(5) Effect of pressure: The effect of pressure is not only related to pressure, but also related to the stress area.

2. Stress

The physical meaning of (1) pressure: pressure is a physical quantity indicating the action of pressure.

(2) Definition: The pressure per unit area of an object is called pressure. There is a limit to the pressure that any object can bear.

(3) Formula and unit

The pressure formula is p=, where f represents the pressure, and the unit is n; S represents the stress area in square meters (m2); P stands for pressure in N/m2. Cow/m2 has a special name Pascal, and the symbol is Pa.

This formula applies to solids, liquids and gases.

(4) Methods of increasing and decreasing pressure

When the pressure is constant, increasing the stress area can reduce the pressure, and reducing the stress area can increase the pressure. Under the condition of a certain stress area, increasing the pressure can increase the pressure, and decreasing the pressure can decrease the pressure.

3. Liquid pressure

(1) Characteristics of liquid pressure: The liquid has pressure on the bottom and wall of the container, and the liquid has pressure in all directions. The pressure of liquid increases with the increase of depth. At the same depth, the pressure of liquid in all directions is equal. The pressure of different liquids is also related to their density. At the same depth, the greater the density of the liquid, the greater the pressure.

(2) Formula and unit

The formula of liquid pressure is p=ρgh, where ρ represents the density of liquid in kg/m3; G is a constant, generally 9.8 n/kg; ; H represents the liquid depth, that is, the distance from the free liquid surface to the required liquid pressure, in meters (m); P stands for pressure in Pascal (Pa).

The liquid pressure is only related to the density and depth of the liquid, and has nothing to do with the weight of the liquid and the cross-sectional area (thickness) of the container.

4. Communicator

(1) Definition: A container with an open top and a communicated bottom is called a connector.

(2) Features: If there is only one liquid in the communication device, when the liquid does not flow, the liquid level in each container is always horizontal.

(3) Application: the kettle body and spout form a communicator, the boiler and the external water level meter form a communicator, and the water tower and the tap water pipe form a communicator. In addition, the ship lock also works by using the principle of communicator.

5. Atmospheric pressure

(1) Concept: The pressure of the atmosphere on an object immersed in it is called atmospheric pressure, or atmospheric pressure for short. Atmospheric pressure is caused by gravity and the fluidity of gas.

(2) Measuring atmospheric pressure

① Two famous experiments

The world-famous experiment to prove the existence of atmospheric pressure is the "Madeborg Hemisphere Experiment", and the experimenter is otto gehrig, the mayor of Madeborg, Germany.

The first experiment to accurately measure atmospheric pressure was "Torricelli Experiment", and the experimenter was Italian scientist Torricelli.

② Barometer: an instrument for measuring atmospheric pressure. There are mainly two kinds of barometers: mercury barometer and air-liquid barometer. The barometer on the oxygen bottle is air-liquid barometer.

③ Standard atmospheric pressure: The height of mercury column measured by Torricelli experiment is 760 mm, which is usually called standard atmospheric pressure. 1 standard atmospheric pressure = 760mmhg =1.013x105pa. Roughly calculated, the standard atmospheric pressure can be taken as 105 Pa.

(3) the change of atmospheric pressure

① Atmospheric pressure and altitude: Atmospheric pressure decreases with the increase of altitude, but the decrease is uneven. Within 3000 meters above sea level, the air pressure drops 100 Pa for every increase in air pressure.

② Atmospheric pressure and boiling point: The boiling points of all liquids decrease when the air pressure decreases and increase when the air pressure increases. The air pressure in the plateau is low, and the boiling point of water is lower than 100℃, so a pressure cooker should be used for cooking.

③ Air pressure is related to the weather. Generally speaking, the air pressure in sunny days is higher than that in cloudy days, and that in winter is higher than that in summer.

(4) Application of atmospheric pressure: Both piston pump and centrifugal pump work by atmospheric pressure.

6. Relationship between liquid (gas) pressure and flow rate

In gas and liquid, the higher the speed, the lower the pressure.

7. buoyancy

(1) Causes of buoyancy: An object immersed in a liquid is subjected to the pressure difference between the upper and lower parts of the liquid.

(2) Buoyancy direction: vertical upward.

(3) Buoyancy can be obtained by the following methods:

Gravimetric method (twice measurement method): F float =G object -F indication;

Archimedes principle: f float =G row = ρ liquid gV row;

Two-force balance method (when suspended or floating): F floating =G row; The causes of buoyancy are: F float = F up -F down;

Force analysis method: When an object is at rest (or moving in a straight line at a constant speed) under the action of three or more forces, it can be solved by the equation of sum of vertical upward forces = sum of vertical downward forces.

(4) Archimedes principle

Content: The buoyancy of an object immersed in a liquid is equal to the gravity of the liquid it displaces, which is Archimedes principle. It also applies to gases.

② Expression: F float =G row = ρ liquid gV row.

(5) Conditions for floating and sinking of objects:

The relationship between buoyancy and the weight of the object and the density of the whole object (when submerged) is as follows: when F floats; ρ liquid; When f is floating =G, it is suspended. At this point, ρ = ρ liquid, and row V = V. ..

An object floats on the surface of a liquid, f float =G object, ρ object.

(6) Application of buoyancy

(1) Ship: It is made of steel whose density is higher than that of water, so that it can float on the water. The size of a ship is usually expressed in terms of displacement. The displacement of a ship refers to the quality of boiling water when it is fully loaded.

(2) Submarines: Change their own weight through water injection or drainage to achieve ups and downs.

(3) Balloons and airships: filled with gas with density less than air.

(4) Densitometer: Densitometer is an instrument for measuring the density of liquid. The densimeter is shallower in a liquid with higher density than in a liquid with lower density, so the top of the scale of the densimeter is smaller and the bottom is larger.

Chapter 15 Work and Mechanical Energy

Knowledge combing:

work

(1) Preliminary concept of work: If a force acts on an object and the object moves a certain distance in the direction of this force, it is said that this force has done work.

(2) Work includes two necessary factors: one is the force acting on the object, and the other is the distance that the object moves in the direction of this force.

(3) Calculation of work: Work is equal to the product of force and the distance traveled by the object in the direction of force (work = force × distance in the direction of force).

The calculation formula of work: W=Fs, f is force, n is unit, m is distance, m is unit, w is the symbol of work, and n is unit. It has a special name called Joule, and the symbol of Joule is J,1j =1n m.

When a vertically lifting object overcomes gravity or does work by gravity, the calculation formula can be written as w = GH, and when it does work against friction, the calculation formula can be written as W=fs.

(4) working principle; When people use machinery, the work they do will not be less than when they don't use machinery (but directly by hand), that is to say, using any machinery will not save labor.

Regardless of the factors such as friction and the weight of the machine itself, the work done by people using the machine is equal to the work done directly by their hands, which is an ideal situation and the simplest one.

2. Mechanical efficiency

(1) Useful work: useful work for people (work that must be done with or without machinery); Extra work: unnecessary but necessary work; Total work: The sum of useful work and extra work is total work.

(2) Definition of mechanical efficiency: The ratio of useful work to total work is called mechanical efficiency.

(3) Calculation formula: η=W useful /W total, where W useful means useful work, W total means total work, and η means mechanical efficiency. It is not difficult to draw from the formula that the result of η has no unit and is expressed as a percentage "%".

3. Power:

The physical meaning of (1) power: it indicates the speed at which an object does work.

(2) Definition of power: the work done per unit time.

(3) Calculation formula: P=, where w stands for work and the unit is coke (j); T stands for time in seconds (s); P stands for power, the unit is watt, and the symbol is w, 1W= 1J/s, that is, 1W = 1J/s, and the commonly used unit of power is kW, and kW= 103W.

4. The concept of energy

If an object can do work, we say it has energy. The unit of energy and work is joule.

An object with energy does not necessarily do work, but an object that does work must have energy.

5. kinetic energy

(1) Definition: The energy possessed by an object due to motion is called kinetic energy.

(2) The factors that affect the kinetic energy are: the mass of the object and the speed of its movement. 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.

(3) All moving objects have kinetic energy, the kinetic energy of stationary objects is zero, and the kinetic energy of objects with a certain mass moving at a uniform speed (whether rising, falling, advancing or retreating at a uniform speed, as long as it is uniform) remains unchanged. The sign of whether an object has kinetic energy is whether it is moving.

6. Potential energy

Potential energy includes gravitational potential energy and elastic potential energy.

(1) gravitational potential energy

① Definition: The energy possessed by an object due to being lifted is called gravitational potential energy.

② The factors that affect the gravitational potential energy are: the mass of the object and the lifted height. The higher the object with the same mass is lifted, the greater the gravitational potential energy; The greater the mass of an object at the same height, the greater the gravitational potential energy.

It is generally believed that the gravitational potential energy of objects on horizontal ground is zero. The gravitational potential energy of an object with a certain mass is increasing when its position rises (whether it rises at a uniform speed, accelerates or decelerates, as long as it rises), while the gravitational potential energy of an object with a certain mass is decreasing when its position falls (whether it falls at a uniform speed, accelerates or decelerates, as long as it falls), while the gravitational potential energy of an object with a constant height remains unchanged.

(2) Elastic potential energy

① Definition: The energy possessed by an object due to elastic deformation is called elastic potential energy.

② The factors influencing elastic potential energy are: elastic deformation (for the same elastic object).

③ For the same spring or rubber band (within a certain elastic range), the greater the deformation, the greater the elastic potential energy. Whether an object has elastic potential energy is a sign: whether it has elastic deformation.

7. Mechanical energy: kinetic energy and potential energy are collectively referred to as mechanical energy.

8. Kinetic energy and potential energy can be transformed into each other.

9. The sources of mechanical energy available to human beings in nature are water energy and wind energy. Large hydropower stations raise the water level by building dams, thus increasing the gravitational potential energy of water, thus converting more mechanical energy into electrical energy when generating electricity.

Chapter 16 Heat and Energy

Knowledge combing:

Matter consists of molecules.

The molecules of all substances are constantly moving irregularly. Molecules attract and repel each other.

2. Diffusion phenomenon

When different substances touch each other, they enter each other. Diffusion phenomenon is characterized by the non-stop irregular movement of molecules, and there are gaps between molecules. The higher the temperature, the faster the diffusion process, indicating that the higher the temperature, the greater the speed of random movement of molecules.

3. Internal energy

The sum of kinetic energy and molecular potential energy of all molecules in an irregular motion object. Because the speed of random motion of molecules is related to temperature. Therefore, the internal energy of an object is also related to temperature. Internal energy is another form of energy different from mechanical energy.

There are two ways to change the internal energy of an object.

Work and heat transfer. Work and heat transfer are equivalent in changing the internal energy of an object, but they are essentially different. Work is the conversion of other forms of energy and internal energy, while heat transfer is only the transfer of internal energy from one object to another.

5. Specific heat

The heat absorbed by a unit mass substance when the temperature rises by 65438 0℃ is called the specific heat capacity of the substance. The unit of specific heat capacity is j/(kg℃).

6. Specific heat capacity is a characteristic of matter.

7. Calculation of heat balance equation

When two objects with different temperatures come into contact, heat will be transferred from the high-temperature object to the low-temperature object until the temperatures of the two objects are equal, at which time it is said that thermal balance has been reached. In the case of no heat loss, the heat Q released by a high-temperature object is equal to the heat Q absorbed by a low-temperature object. Q put =Q suck.

8. heat engine

A machine that converts internal energy into mechanical energy. For example, the internal energy released by fuel combustion is converted into mechanical energy to do work.

9. calorific value of fuel

1kg heat released by complete combustion of a certain fuel. Calorific value is a characteristic of fuel. The unit is Joule/kg.

10. Heat engine efficiency

It is impossible for any heat engine to use all the internal energy released by fuel for useful work. For example, the exhaust gas of gasoline engine and diesel engine will take away a considerable amount of internal energy, and the cooling system will also release a large amount of internal energy. The ratio of the part used for useful work in a heat engine to the energy released by complete combustion of fuel is called heat engine efficiency.

1 1. Under certain conditions, various forms of energy can be transformed into each other.

conservation of energy

Energy will neither disappear nor be generated out of thin air. It will only change 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 17 energy and sustainable development

Knowledge combing:

1. original energy

Energy that can be obtained directly from nature. For example: fossil energy, wind energy, solar energy, geothermal energy, nuclear energy, etc.

2. Secondary energy

Energy that cannot be obtained directly from nature and must be obtained through a certain amount of energy consumption. For example: electricity.

3. non-renewable energy

The less you use, the less energy you will get from nature in a short time. For example: fossil energy (oil, natural gas), nuclear energy.

4. Renewable energy

Energy that can be obtained continuously in nature. For example: kinetic energy of water, wind energy, solar energy and biomass energy (chemical energy stored in biological substances such as food).

5. Nuclear energy

Because atoms and neutrons in atoms are closely combined by nuclear force, it is nuclear fission or polymerization that needs to absorb or release energy, which is called nuclear energy.

6. Two ways to obtain atomic energy

One is to bombard a relatively large nucleus (heavy nucleus) with neutrons, so that it can split into two nuclei of medium size and release huge energy at the same time. The other is to combine some very small nuclei (light nuclei) into new nuclei at ultra-high temperature, releasing huge nuclear energy, which is fusion.

7. Chain reaction

Using neutrons to bombard uranium 235 nucleus, nuclear energy is released when uranium nucleus splits, and at the same time, several new neutrons will be produced, which will bombard other uranium nuclei ... So a series of uranium nuclei continue to split and release a lot of nuclear energy, which is a chain reaction.

8. The sun is a huge "nuclear stove"

Inside the sun, hydrogen nuclei fuse at ultra-high temperature, releasing huge nuclear energy.

9. How to use solar energy

Solar energy collector, solar cell.

10. Development of energy conversion technology

Three energy revolutions (artificial fire-steam engine-nuclear energy)

1 1. Directionality and irreversibility of energy transfer and energy transformation

Internal energy can only be automatically transferred from a high-temperature object to a low-temperature object, not the other way around. When a car brakes, kinetic energy is converted into internal energy of the ground and air, not the other way around. The use of energy is conditional and comes at a price. Not all energy can be used.

12. Energy situation in the world and China

Since 1973, mankind has demanded 500 billion barrels of oil from the earth, and the remaining oil can be mined for 44 years at the current level; Natural gas can only be mined for 56 years, which shows that with the increase of population and economic development, energy consumption is increasing.

13. Impact of energy consumption on the environment

In the process of energy revolution, human beings have brought convenience and trouble, such as acid rain, soil acidification and greenhouse effect. Human beings must raise awareness of energy conservation and environmental protection.