In fact, the "collar" of chemistry examination is the newly promulgated "High School Chemistry Examination Standard". Although the chemical requirements of different provinces are different, the "top four" are the same: chemical language ability-the ability to identify and use chemical terms; Scientific thinking ability-the ability to summarize, classify, compare, judge and reason chemical knowledge; Chemical experiment ability-the ability to complete chemical experiments; Chemical calculation ability-the ability to solve stoichiometric problems by using chemical knowledge and common mathematical methods. These four "strengths" are reflected in the four levels of memory, understanding, application and synthesis of each knowledge point, and then review them in a targeted manner.

Of course, the "explanatory questions" and "example papers" in the "High School Chemistry Examination Standards" must be rehearsed independently until they are truly understood.

Grasping the "High School Chemistry Examination Standard" will seize the "collar" of the chemistry examination!

Second, sort out the "five pieces" of knowledge

"Chaos, confusion and hard to remember" seems to be a major feature of high school chemistry. Actually, it is not! As long as in-depth study, it is not difficult to find that chemistry can be divided into the following five knowledge systems:

1. Basic concepts and principles

There are more than 80 concepts in high school chemistry, and there are 34 points in the exam, including: ① substances and their changes; ② Material structure and periodic law of elements; ③ Chemical balance and ionization balance; ④ Principle and application of primary battery.

2. Knowledge of elemental compounds

It can be divided into "nonmetallic elements and their compounds" (mainly examining nitrogen group elements and their compounds) and "metallic elements and their compounds" (mainly examining the universality of metals, aluminum and their compounds and iron).

Knowledge points of high school physics examination (mechanics part) 2

Chapter I Power

Section 3 Newton's third law

1. The content of Newton's third law

The action and reaction between two objects are always equal in size and opposite in direction, and act on a straight line. This is Newton's third law.

2. The application of Newton's third law,

Action and reaction always appear in pairs at the same time. As long as it is strong, this force must have a reaction. According to Newton's third law, we can know the magnitude and direction of its reaction. If we find the person who exerted this force, we can know the person who received the reaction. The magnitude and nature of force and reaction are the same, not the effect.

3. The difference between action, reaction and balance.

A pair of acting force, reaction force and a pair of balancing force have the characteristics of "equal size, opposite direction and acting on a straight line", which is easy to be confused. They can be distinguished from each other in the following four aspects:

A pair of action and reaction, a pair of balance.

The acting object acts on two different interacting objects and the same object.

The nature of forces must be the same, but they can be different.

The force acts on two objects respectively, and the effect on each object cannot be offset. It is impossible to find the effect of the resultant force on the same object, but this effect can cancel each other out and the resultant force is zero.

The change of force occurs and disappears at the same time, and the change at the same time can be changed independently.

4. Impulse and work of a pair of action and reaction.

The total impulse of a pair of acting and reacting forces in the same process (same time or same displacement) must be zero, but the total work done may be zero or positive or negative. This is because the action time of acting force and reaction force must be the same, and the magnitude and direction of displacement may be different.

Section 4 System of Mechanical Units

1, base unit and derived unit

(1) basic unit: the selected units of several basic physical quantities are called basic units.

(2) Derived unit: The unit derived from the unit relation of physical quantity determined by physical formula is called derived unit.

2. The basic unit of mechanics in the international system of units.

(1) In mechanics, the units of length, mass and time are chosen as the basic units. In the international system of units, meters, kilograms and seconds are the basic units. Besides, what if we use centimeters? g？ In the second system, centimeters, grams and seconds are the basic units. High school physics also has units of current, temperature and substance, such as ampere, kelvin and mole.

(2) In mechanics, units such as speed (m/s), acceleration (m/s 2) and force (n) are all derived units.

(3) In physical calculation, all known quantities are expressed in the same unit system. To correctly apply the physical formula, the unit of the required quantity must be the corresponding unit in this unit system. The units of all physical quantities can be composed of basic units by formulas, and we can also check whether the required conclusions are wrong by whether the units are consistent with the physical quantities.

Section 5 Application Scope of Newton's Law of Motion

1, the scope of application of Newton's law of motion

Newton's law of motion is the basic law of classical mechanics, which is completely suitable for dealing with the low-speed motion of macroscopic objects, but not when the speed is close to the speed of light; Classical mechanical laws are generally not applicable to microscopic particles.

2. The relationship between the mass and velocity of an object.

According to Einstein's special theory of relativity, the mass of an object increases with the increase of speed. At low speed, the mass increases slightly, but when the speed is close to the speed of light, the mass will increase obviously.

Chapter IV Object Balance

The first section * * * the balance of objects under the action of point force

1. Equilibrium state and equilibrium conditions of objects

(1) * * Point force: Several forces act on the same point of an object, or their lines of action intersect at the same point (the point is not necessarily on the object). These forces are called * * * point forces.

(2) Balance: The state in which an object is stationary or moving in a straight line at a uniform speed is called balance.

(3) Equilibrium condition: the resultant force of all forces (* * * point force) on the object is zero, that is, under the action of equilibrium force, the object is in equilibrium.

2. The application of object equilibrium conditions

(1) Two-force balance: When an object is in equilibrium under the action of only two * * * point forces, the two forces must be equal in magnitude and opposite in direction.

(2) Three-force balance: When an object is in a state of balance under the action of three * * * point forces, the resultant force of any two of the three forces is equal in magnitude and opposite in direction to the third force.

(3) Multi-force balance: When an object is in equilibrium under the action of several * * * point forces, the resultant force of any force and its residual force is equal in size and opposite in direction.

(4) Force balance above three * * * points: In addition to the two-force balance mentioned in (2) and (3), it can also be treated by orthogonal decomposition synthesis, that is, the balance conditions of FX =0 and FY =0 are applied.

3. Inference of equilibrium conditions

(1) When an object is in equilibrium under the action of multiple * * * point forces, the resultant force of one of the forces and its residual force is equal in magnitude and opposite in direction.

(2) When an object is in equilibrium under the action of three non-parallel forces in the same plane, these three forces must be * * * point forces.

(3) When an object is in equilibrium under the action of three * * * point forces, the directed line segments of these three forces must form a closed triangle, that is, the vectors representing these three forces are connected end to end, which can form a closed triangle. Sine theorem method can be used.

In the triangle as shown in the figure, there are:

4. Solutions to problems

When an object is balanced under the action of two * * * point forces, the two forces must be equal in magnitude and opposite in direction; When an object is balanced under the action of three * * * point forces, the parallelogram rule or triangle rule is often adopted; When an object is in equilibrium under the action of four or more * * * point forces, orthogonal decomposition method is often used.

Section 2 Balance of Objects with Fixed Rotating Axis

1. Arm and moment

(1) The distance from the axis of rotation to the line of action of the force is called the arm of force.

(2) The product of force and arm of force is called moment. The rotating effect of force on an object depends on the magnitude of torque. The unit of torque is Newton? Rice, cattle for short? M, the symbol is n? Meter (short for meter))

Chapter V Curved Motion

Curve motion in the first quarter

1, the speed direction of curve motion

(1) In curvilinear motion, the instantaneous velocity direction of a moving particle at a certain point is the tangent direction of the curve passing through that point.

(2) The speed direction of curvilinear motion is always changing, and the speed of motion is always changing regardless of the speed, so curvilinear motion is variable-speed motion.

2. Conditions for the motion of objects along curves

(1) When the direction of the resultant force acting on an object is not in a straight line with its speed direction, this resultant force can always produce the effect of changing the speed direction, and the object must move in a curve.

(2) When an object moves in a curve, the acceleration direction and the velocity direction generated by its resultant force are not in the same straight line.

(3) The motion state of an object is determined by its stress and initial motion state.

The nature of the motion of an object is determined by the acceleration (when the acceleration is zero, the object is stationary or moving at a uniform speed; When the acceleration is constant, the object moves at a uniform speed; When the acceleration changes, the object moves with variable acceleration.

The trajectory (straight line or curve) of an object is determined by the directional relationship between its speed and acceleration (when the speed and acceleration are in the same straight line, the object moves along a straight line; When the velocity and acceleration direction form a certain angle, the object moves in a curve).

Is the combined motion of two mutually angled linear motions a linear motion or a curvilinear motion?

It depends on whether their convergence speed and acceleration direction are linear (see figure).

Common types are:

(1) A = 0: moving in a straight line at a uniform speed or at rest.

⑵a is a constant: it is uniform and variable in nature and can be divided into:

(1) V and a are in the same direction, uniformly accelerating linear motion;

(2) V and A move in opposite directions and in a straight line at a uniform speed;

(3) The curve motion in which V is at an angle with A and changes at a constant speed (the trajectory is between V and A, tangent to the direction of velocity V, and the direction gradually approaches to the direction of A, but it is impossible to realize. )

(3) a change: the nature is variable acceleration. Such as simple harmonic vibration, the magnitude and direction of acceleration change with time.

The relationship between the motion form of an object and its stress condition and initial motion state

Initial state

sports

form

The condition of the force is in a straight line with the initial velocity direction (or the initial velocity is zero), but the force and the initial velocity direction are not in a straight line.

Constant force, uniform linear motion and uniform curvilinear motion

uniformly accelerated rectilinear motion

Special case: Free falling body with uniform deceleration and linear motion.

Special cases: vertical upward throwing, horizontal throwing and inclined throwing.

Linear motion with variable force and acceleration and curvilinear motion with variable acceleration.

Simple harmonic motion moves in a uniform circle.

Zero resultant force, static or uniform linear motion

Second, the synthesis and decomposition of motion

1, combined motion and split motion

When the actual motion of an object is complicated, we can equate it with participating in several simple motions at the same time. The former is the actual motion, which is called combined motion, and the latter is called the component motion of the actual motion of an object.

2. The concepts of synthesis and decomposition of motion.

As we all know, the motion of dividing motion is called the synthesis of motion; As we all know, the segmentation motion of combined motion is called motion decomposition. This two-way equivalent operation process is an important method to study complex motion.

3. Application of motion synthesis and decomposition

(1) To synthesize and decompose the motion is to sum or subtract the displacement, velocity, acceleration and other vectors that describe the motion with the parallelogram rule. The composition and decomposition of motion follow the following principles:

(1) Principle of independence: Several sub-movements that make up a combined movement are independent and irrelevant, and any sub-movement of an object is carried out according to its own laws and will not be changed because of the existence of other sub-movements.

② Isochronous principle: Synthetic motion is the result that the same object completes several partial motions at the same time, so it is meaningful to synthesize several motions that the same object participates in at the same time.

③ Vector principle: Physical quantities such as displacement, velocity and acceleration that describe the state of motion are all vectors, and these physical quantities should be calculated according to the vector law, that is, the parallelogram law, when synthesizing and decomposing motion.

(2) The nature of combined motion can be determined by the nature of component motion: the combination of two uniform linear motions is still uniform linear motion; The combined motion of uniform linear motion and uniform variable linear motion is uniform variable motion; The combined motion of two uniformly variable linear motions is uniformly variable motion.

(3) Crossing the river

As shown in the right figure, if v 1 represents the water speed and v2 represents the ship speed, then:

① The crossing time is only determined by the component v⊥ perpendicular to the bank of v2, that is, it has nothing to do with v 1, so v2⊥ has the shortest crossing time when it comes ashore, and the shortest crossing time has nothing to do with v 1.

② The crossing distance is determined by the direction of the actual trajectory. When V 1 < V2, the shortest distance is d; When v 1 > v2, the shortest distance is (as shown on the right).

(4). Joint movement problems

Refers to the problem of pulling the rope (pole) or pulling the rope (pole). Because the rope in high school is inextensible and the rod is inextensible and compressible, that is, the length of the rope or rod will not change, the principle of solving the problem is: decompose the actual speed of the object into two components perpendicular to the rope (rod) and parallel to the rope (rod), and solve it along the direction of the rope (rod) according to the same component speed.

In the second quarter, the motion of flat throwing objects

1. Definition, characteristics and trajectory of flat throwing motion

A (1) object has an initial velocity in the horizontal direction, and the motion that occurs only under the action of gravity is called flat throwing motion.

(2) Flat throwing motion is a kind of curvilinear motion which changes with acceleration g and a curve (semi-parabola) at a uniform speed. Generally speaking, flat throwing motion is regarded as the synthesis of uniform linear motion along the horizontal direction and free falling motion in the vertical direction.

2. Conditions for objects to do flat throwing motion

(1) The conditions for an object to make a flat throwing motion are as follows: ① only subjected to gravity; ② There is an initial velocity in the horizontal direction.

(2) When the object is subjected to a constant force and the initial velocity direction is perpendicular to the direction of the constant force, the motion is the same as that of a flat projectile, and it belongs to the uniform variable-speed curve motion of parabolic trajectory.

3. The law of flat throwing motion

In the coordinate system with the throwing point as the origin, the horizontal direction as the X-axis, the initial velocity v0, the direction as the positive direction of the X-axis and the vertical direction as the positive direction of the Y-axis downward, the law of flat throwing motion is described as follows:

4. The application of the law of flat throwing motion

(1) to deal with the problem of flat throwing motion, we should grasp the characteristics of hand throwing motion, decompose it into two linear motions, and use the law of uniform linear motion in the horizontal direction and the law of uniform acceleration of linear motion in the vertical direction. For example:

(1) t = instantaneous velocity v at the middle moment of uniform linear motion.

② The displacement difference Δ t in any two consecutive equal time intervals: s Ⅱ-si = s Ⅲ-s Ⅱ = Δ s = a? δT2

③ Uniformly accelerated linear motion with zero initial velocity, displacement ratio of the first 1, 2, …n equal time intervals.

s 1:s2:s3:………sn=l:4:…n2

Displacement ratio of 1, 2, …N equal time interval.

sⅰ:sⅱ:……sN = 1:3:……(2n-l)。

(2) When the falling point of a flat throwing object is on a horizontal plane, the time of the object in air movement is determined by the falling height h of the free falling body, and has nothing to do with the initial velocity v0; t =； The horizontal range of an object is determined by altitude and initial velocity: x =；;

(3). Useful inference

The distance from the intersection of the reverse extension line in the velocity direction and the initial velocity extension line to the throwing point of the flat throwing object at any moment is equal to half of the horizontal displacement.

It is proved that if the horizontal displacement of the object at time t is S and the vertical displacement is H, then the horizontal component vx=v0=s/t and the vertical component vy=2h/t of the final velocity, so there is

The third quarter uniform circular motion

First, the definition and nature of uniform circular motion

1. A particle moves in a circle. If the length of the arc it passes through is equal in equal time, this motion is called uniform circular motion, which is a basic curvilinear motion.

2. Uniform circular motion has the following characteristics: ① The trajectory is a circle; (2) The linear velocity and acceleration are constant, and the direction is constantly changing, so it belongs to the curve motion with variable acceleration and constant angular velocity in uniform circular motion; ③ The condition of uniform circular motion is that the particle is subjected to a resultant force with constant magnitude and always perpendicular to the speed direction; ④ The motion state of uniform circular motion appears repeatedly, and the uniform circular motion has periodicity.

Second, the description of uniform circular motion

1. linear velocity. Concepts of angular velocity, period and frequency

(1) linear velocity v is a physical quantity describing the velocity of a particle moving along a circle, and it is a vector with the magnitude: its direction is tangent to the trajectory, and the unit symbol in the international system of units is m/s;

(2) Angular velocity ω is a physical quantity describing the rotation speed of a particle around the center of a circle, and it is a vector with the size as follows:

In the international system of units, the unit symbol is rad/second;

(3) The period T is the time taken for a particle to move around a circle, and the unit symbol in the international system of units is S;

(4) Frequency f is the number of times a particle completes a complete circular motion in a unit time, and the unit symbol in the international system of units is Hz;

(5) The rotational speed n is the number of revolutions of a particle per unit time, and the unit symbols are r/s and r/min.

2. The relationship between speed, angular velocity, period and frequency.

Linear velocity, angular velocity, period and frequency describe the velocity of particle motion from different angles, and there is a relationship between them: v = r ω.

As can be seen from the above, when the angular velocity is constant, the linear velocity is proportional to the radius; When linear velocity is constant, angular velocity is inversely proportional to radius.

For two wheels directly driven by belt (including chain drive and friction drive), the linear velocity of each point on the edge of the two wheels is equal; All points on the same axis (all wheels rotate synchronously around the same axis) have the same angular velocity (except the points on the axis).

Third, centripetal force and centripetal acceleration.

1. centripetal force

The centripetal force (1) is the reason for changing the direction of motion and producing centripetal acceleration.

(2) The centripetal force points to the center of the circle and is always perpendicular to the moving direction of the object, so the centripetal force only changes the direction of the speed.

(3) According to Newton's law of motion, the causal relationship between centripetal force and centripetal acceleration is that their directions are the same: they are always perpendicular to the speed and point to the center of the circle along the radius.

(4) For uniform circular motion, all resultant forces acting on the object are regarded as centripetal force, so the resultant force on the object with uniform circular motion should be constant and always perpendicular to the speed direction.

2. centripetal acceleration

(1) centripetal acceleration is produced by centripetal force, which describes the speed of linear velocity change and is a vector.

(2) The centripetal acceleration direction is consistent with the centripetal force direction and always points to the center of the circle along the radius; What is the size of centripetal acceleration?

(3) Generally speaking, when the resultant force acting on a circular moving object does not point to the center of the circle, it can be decomposed orthogonally along the radial direction and the tangential direction, and its component along the radial direction is centripetal force, which only changes the direction of the velocity, but does not change the magnitude of the velocity; Its component along the tangential direction is a tangential force, which only changes the size of the speed and does not change the direction of the speed. Their corresponding centripetal acceleration describes the speed change, and tangential acceleration describes the speed change.

3. Comparison of centripetal force formulas

(1) According to formulas a=ω2r and a=v2/r, the centripetal acceleration of a particle is proportional to the radius when the angular velocity is constant; When the linear velocity is constant, the centripetal acceleration of the particle is inversely proportional to the radius.

(2) The external force on an object moving in a uniform circle is all regarded as centripetal force, so the external force on the object should be constant and always perpendicular to the speed direction; According to the formula, if the external force F acting on the object is greater than the centripetal force required to move on the circular orbit, the object will move to a new circular orbit with a reduced radius (where the angular velocity of the object will increase), so that the external force acting on the object is exactly equal to the centripetal force required on the orbit, indicating that the object will move near the center of the circle at this time; On the other hand, if the resultant force acting on an object is less than the centripetal force required to move along a circular orbit, the orbit radius of the object will increase and it will gradually move away from the center of the circle. If the resultant force suddenly disappears, the object will fly out in the tangential direction, which is centrifugal motion.

4. Solving practical problems with centripetal force formula

When solving the dynamic problem of circular motion according to the formula, four judgments should be made:

(1) Determine the plane where the center of the circle and the trajectory of the circle lie;

(2) Determine the source of centripetal force;

(3) Take the direction pointing to the center of the circle as positive, and determine the positive and negative components involved in the centripetal force;

(4) Determine the dynamic equation satisfying Newton's law.

The relationship between the centripetal force of an object in circular motion and centripetal acceleration also follows Newton's second law: Fn=man When making an equation, according to the force analysis of the object, write the resultant force provided by the outside on the left side of the equation, and write the centripetal force required by the object on the right side (various forms can be selected).

Fourth, the example of circular motion.

1. Analysis on the source of centripetal force in actual exercise

(1) centripetal force is named according to the action of force. A force, a component of a force, or the resultant force of several forces acts on an object, which can only change the direction of the object's speed but not the speed. This is centripetal force. The centripetal force is definitely a variable force, and its direction is always changing.

(2) The centripetal force comes from the external force actually acting on the object. When dealing with specific problems, we must first make clear what forces are acting on the object and whether these forces have components perpendicular to the speed direction. All components perpendicular to the velocity direction have the function of changing the velocity direction and will participate in the formation of centripetal force.

2. Problems related to special points in variable-speed circular motion.

(1) centripetal force and centripetal acceleration formula are also applicable to variable-speed circular motion. When calculating the centripetal acceleration size of a particle in a variable-speed circular motion moment, the instantaneous value of that moment must be used for V (or ω) in the formula.

(2) The variable-speed circular motion of an object in a vertical plane under the action of gravity and elasticity usually only studies two special states, namely, the highest point and the lowest point of the trajectory. In these two positions, gravity, elasticity and centripetal acceleration providing centripetal force are all on the same vertical line. Centripetal force is the algebraic sum of elasticity and gravity, and the speed and acceleration of an object are different in these two positions.

The characteristics of this kind of problems are: due to the conservation of mechanical energy, the speed of the object's circular motion has been changing, and the speed of the object is the smallest at the highest point and the largest at the lowest point. At the lowest point, the centripetal force of the object is upward, while gravity is downward, so the elastic force must be upward and greater than gravity; At the highest point, the centripetal force is downward and the gravity is downward, so the direction of elastic force cannot be determined. It should be discussed in three situations.

(1) The elastic force can only be downward, such as a rope pulling the ball. In this case, one of them is yes, otherwise it will not pass the highest point.

(2) the elasticity can only be upward, such as a car crossing a bridge. In this case, there are:, otherwise the car will leave the bridge deck and do flat throwing.

(3) The elastic force can be upward or downward, such as rotating in the tube (or connecting the ball with a rod and piercing the ball with a ring). In this case, the speed v can take any value. But it can be further discussed as follows: (1) The elastic force on the object must be downward; When the elastic force of the object is bound to be upward; When the elastic force on the object is exactly zero. (2) When the elastic force F

3. Conical pendulum

Conical pendulum is a typical uniform circular motion, and its trajectory is in the horizontal plane. Its characteristic is that the resultant force of gravity and elasticity on the object is taken as centripetal force, and the direction of centripetal force is horizontal. It can also be said that the horizontal component of elastic force provides centripetal force (the vertical component of elastic force and gravity are mutually balanced forces).

Chapter VI Law of Universal Gravitation

Section 1 Law of Universal Gravitation

I. Planetary motion

1. Geocentric theory and Heliocentrism

Geocentric theory holds that the earth is the center of the universe, motionless, and the sun, moon and other planets all move around the earth. Heliocentrism believes that the sun is stationary, and the earth and other planets move around it. Heliocentrism is the foundation of forming a new world outlook and a challenge to religion.

2. Kepler's first law

Kepler's first law states that the orbits of all planets around the sun are ellipses, and the sun is at the focus of all ellipses. This law, also known as the "orbital law", correctly describes the shape of planetary orbits.

3. Kepler's third law

Kepler's third law points out that the ratio of the cubic of the semi-major axis of all planetary orbits to the quadratic of period of revolution is equal, that is, R3/T2 = K. This law is also known as the "periodic law". Kepler's third law of planetary motion is based on the data recorded by Tycho's observation of planetary motion for 20 consecutive years, and the conclusion is drawn through hard calculation.

Second, the law of universal gravitation

1. The content of the law of universal gravitation

(l) Gravity is the interaction between objects because they have mass. Its size is related to the mass of the object and the distance between two objects: the greater the mass of two objects, the greater the attraction between them; The farther the distance between two objects is, the smaller the attraction between them. Generally, the gravity between two objects is very small, and the role of gravity is decisive in the celestial system.

(2) The formula of the law of universal gravitation is that the magnitude of universal gravitation between two objects is directly proportional to the product of the mass of these two objects and inversely proportional to the square of their distance.

2. Gravity constant and its determination

(1) gravitational constant g = 6.67259×10-1n? M2/kg2, usually g = 6.67×10-11n? m2/kg2。

(2) The value of the gravitational constant g was first accurately determined by the British physicist Cavendish with a torsion balance device. The determination of g not only proves the existence of universal gravitation through experiments, but also makes the law of universal gravitation practical.

3. The application of the law of universal gravitation

The law of universal gravitation plays a decisive role in studying the motion of celestial bodies. It unifies the law of motion of objects on the ground with the law of motion of celestial bodies, which is the basis of human understanding of the universe. The following applications of the law of universal gravitation in astronomy:

(1) Find out the mass and density of the central planet by using the law of universal gravitation.

When one planet moves in a uniform circle around another planet, let the mass of the central planet be M, the radius be R, the mass around the planet be M, the linear velocity be V, the period of revolution be T, and the distance between the two planets be R. The law of universal gravitation is as follows:

It can be concluded that the mass of the central planet can be obtained from r, v or r, t; If the surrounding planets are close to the surface of the central planet, that is, r≈R, then the average density ρ of the central planet can be obtained by the following formula.

(2) Discovering unknown celestial bodies: The law of universal gravitation can not only explain the known phenomena of celestial bodies, but also predict the orbits of celestial bodies according to the relationship between force and motion, thus discovering new celestial bodies.

(3) the relationship between gravity and gravity

Generally, the planet is constantly rotating, and the objects on the surface of the planet need centripetal force with the rotation of the planet, so the gravity on the objects on the surface of the planet has two functions: one is gravity and the other is centripetal force. As shown in the figure, one component of the gravitational force on the surface of the planet is gravity, and the other component is the centripetal force needed to make the object rotate with the planet. that is

The magnitude of centripetal force f on the earth's surface does not exceed 0.35% of gravity, so it can be considered that gravity and gravitation are equal in calculation. That's mg = g. So the acceleration of gravity is g = g, so it can be seen that g decreases with the increase of H. If the angular velocity of rotation of some planets is large, the centripetal force component of gravity will be large and the gravity will be reduced accordingly, so gravity can no longer be considered equal to gravity. If the rotation speed of a planet is so high that the gravitational force on the object at its equator is exactly equal to the centripetal force required for the object to rotate with the planet, then the planet is in a critical state of self-collapse.

(4) Binary star

In the universe, there are often two planets that are very close and have the same mass. They are far away from other planets, so the gravity of other planets on them can be ignored. In this case, they will make uniform circular motion around a fixed point on a straight line in the same period. This structure is called a binary star.

(1) Because the binary star and the fixed point always keep a three-point line, the rotation angles at the same time must be equal, that is, the angular velocities of the binary stars moving in a uniform circle must be equal, so the periods must be the same.

(2) Since the centripetal force of each star is provided by the gravitational force of the interaction between two stars, the magnitude must be equal, which can be obtained by F=mrω2, that is, the fixed point is closer to the star with large mass.

(3) Pay attention to the formula: R in the expression of the law of gravity refers to the distance between two stars, which should be L according to the meaning of the question, while R in the expression of centripetal force refers to the radius of their respective circular movements, which is r 1 and r2 in this question, and must not be confused.

When we only study the Earth-Sun system or the Earth-Moon system (compared with other stars, their gravity can be ignored), it is actually a binary star system, but the mass of the central planet is much greater than that of the surrounding planets, so the fixed point is almost at the center of the central planet. Can be considered fixed.

In the second quarter, satellites and cosmic speed

First of all, satellites

(1) When all gravity on the earth is regarded as centripetal force, an object can move along a circle (or ellipse) with the center of the earth (or a focus) as the center, and become an artificial earth satellite. When the satellite runs in a circular orbit with a distance r from the center of the earth, the acceleration a of the satellite motion can be obtained; The linear velocity of satellite motion can be obtained; The angular velocity of the satellite motion can be obtained. The laws of centripetal acceleration, velocity, period and angular velocity of satellites with different circular orbits changing with orbital radius are shown in the following table:

List of laws of motion of artificial earth satellites

Relationship between Orbital Radius R and radius of the earth R0

speed up

linear velocity

circulate

angular velocity

It can be clearly seen from the table that the acceleration of satellite motion is inversely proportional to the square of orbital radius; However, it is easy to remember the law of the orbit speed and period of the satellite in the orbit with radius R. As can be seen from the table, the larger the orbit radius, the smaller the acceleration, linear velocity, angular velocity and period of the satellite.

(2) Application of satellites

① Satellite orbit: The applied satellite orbits include geosynchronous orbit, polar orbit and other orbits, as shown in the figure.

Types of applied satellites: communication satellites, meteorological satellites, resource satellites, navigation satellites and reconnaissance satellites.

(2) Near-Earth satellites. The orbital radius R of the near-earth satellite can be approximately considered to be equal to radius of the earth R, because it is close to the ground, so there is. They are the maximum linear velocity and the minimum period of the satellite's uniform circular motion around the earth.

(3) Synchronous satellites. The meaning of "synchronization" is to remain relatively stationary with the earth (also called geostationary orbit satellite), so its period is equal to the rotation period of the earth, that is, T=24h. According to (1), its orbital radius is uniquely determined. Through calculation, it can be concluded that the altitude of the synchronous satellite from the ground is H = 3.6×107m ≈ 5.6r (36,000km), and its orbit must be directly above the equator of the earth.

Second, the speed of the universe.

1. First