What are the types of questions in Newton s theorem? 10

1. Newton's first law of motion: When all objects are not affected by external forces, they always maintain a uniform linear motion or a state of rest, which is the law of inertia. Illustrates that all objects have inertia.

2. Newton's second law of motion: the acceleration of an object is directly proportional to the resultant external force on the object, inversely proportional to the mass of the object, and the direction of acceleration is the same as the direction of the resultant external force.

3. Newton's third law of motion: the force and reaction force between two objects, in the same straight line, are equal in magnitude and opposite in direction.

Newtonian mechanics belongs to the category of classical mechanics, which takes the particle as the research object, focuses on the action relationship of force, and emphasizes the consideration of the force on each particle point when dealing with the problem of the particle system, and then deduces the motion state of the entire particle system. Newtonian mechanics holds that mass and energy exist independently and are conserved separately; Inertial frame of reference that applies only to the motion of an object; Newtonian mechanics mostly uses intuitive geometric methods, which is more convenient and simple than analytical mechanics when solving simple mechanical problems.

。。Newton's laws of motion include Newton's first law of motion, Newton's second law of motion, and Newton's third law of motion, which were summarized by Isaac Newton in his book Principia Mathematica of Natural Philosophy in 1687. The first law states the meaning of force:

Force is what changes the state of motion of an object; The second law states the effect of force: force causes an object to gain acceleration; The third law reveals the nature of force: force is an interaction between objects.

The laws in Newton's laws of motion are independent of each other, and their internal logic is self-consistent. Its scope of application is the range of classical mechanics, and the applicable conditions are particles, inertial reference frames, and macroscopic and low-speed motion problems. Newton's laws of motion explain the complete system of Newtonian mechanics and the basic laws of motion in classical mechanics, which are widely used in various fields.

Sir Isaac Newton, the proposer of Newton's laws of motion, president of the Royal Society, a famous British physicist, an encyclopedic "all-rounder", is the author of "Mathematical Principles of Natural Philosophy" and "Optics".

Newton's theorem states that the trajectory of the center of a conic curve tangent to the four sides of a perfect quadrilateral is a straight line, which is the line common to the midpoints of the three diagonals of a complete quadrilateral. It covers the theorem that the midpoint of the diagonal line of a circumscribed quadrilateral of a circle is connected through the center of the circle.

Newton's theorem generally refers to the law of gravity, which means, for example, the theorem that is like an apple falling to the ground.

The first law: any object remains at rest or moves in a straight line at a uniform speed, unless a force acting on it forces it to change this state.

The second law: The change in motion is proportional to the applied dynamic force and occurs in the direction of the straight line along which the force is directed.

The third law: for every action, there is always an equal reaction to which it is opposed; In other words, the interaction between two objects towards each other is always equal and pointing in opposite directions.

Newton's laws of motion include Newton's first law of motion, Newton's second law of motion, and Newton's third law of motion, which were summarized by Isaac Newton in his book Principia Mathematica of Natural Philosophy in 1687.

1. Newton's first law.

If the external force exerted on an object is zero, the velocity of the object remains unchanged (law of inertia).

Newton's first law states that if the external force exerted on an object is zero, the speed of motion of the object does not change. Velocity is a vector quantity, and velocity includes the magnitude and direction of motion.

According to this law, it can be concluded that an object at rest remains at rest until an external force is exerted on the object. An object in motion maintains the magnitude and direction of its velocity until an external force is applied to the object.

2. Newton's second law.

The external force exerted on an object is equal to the product of the mass of this object and its acceleration.

Newton's second law states that the external force exerted on an object is equal to the product of mass and acceleration. This law is also known as the "Law of Acceleration". In terms of the equation, f = ma, where f is the external force, m is the mass, and a is the acceleration.

The second law can also be expressed in terms of momentum, i.e., the external force exerted on an object is equal to the variability of momentum:

f=dp/dt；where p is momentum and t is time.

Since momentum is equal to mass multiplied by acceleration, if the mass does not change, the law of acceleration can be obtained, and if the mass changes with the flow of time, then the system is a variable mass system, and the time-varying mass must be taken into account.

3. Newton's third law.

When two objects interact with each other, the forces exerted on each other are equal in magnitude and in opposite directions (action and reaction).

Newton's third law states that when two objects interact with each other, the forces exerted on each other are equal in magnitude and in opposite directions. According to the third law, a force is an interaction between an object, and the force must occur in pairs, one of which is called the "action force" and the other force is called the "reaction force".

These two forces are equal in magnitude and opposite in direction. Between these two forces, any force can be called an acting force, and the corresponding force naturally becomes a concomitant reaction force.

This pairing force and reaction force is called a "pairing force". The third law is also known as the "law of action and reaction".

The content of Newton's three laws is:

1. Newton's first law of motion, referred to as Newton's first law, is also known as the law of inertia and the law of inertia. Contents: Any object must remain in a uniform linear motion or at rest until an external force forces it to change its state of motion.

The first law explains the meaning of force: force is what changes the state of motion of an object. The second law states the effect of force:

The force causes the object to gain acceleration.

2. Newton's second law of motion: the acceleration of an object is proportional to the force, inversely proportional to the mass of the object, and proportional to the reciprocal of the mass of the object; The direction of acceleration is the same as that of the applied force. The second law states the effect of force:

The force causes the object to gain acceleration.

3. Newton's third law of motion: The force and reaction force between two interacting objects are always equal in magnitude and opposite in direction, acting on the same straight line. The third law reveals the nature of force: force is an interaction between objects.

The edifice of classical mechanics is built on the basis of Newton's laws. Therefore, the scope (or condition) of Newton's motion is the scope of application of classical mechanics. The description of the scope of application of classical mechanics in high school physics textbooks is:

Classical mechanics is only suitable for solving the problem of low-speed motion of macroscopic objects, and cannot be used to deal with the problem of high-speed motion. Classical mechanics only applies to macroscopic objects, and generally not to microscopic particles. Whether this description of defining the scope of application of classical mechanics is completely correct, there is something worth worthing: can classical mechanics really not be used to deal with the problem of high-speed motion?

But in fact, high school physics textbooks deal with the acceleration and deflection of microscopic particles (such as protons, electrons, or particles) in an electric field or the uniform circular motion in a uniform magnetic field, even if the velocity of the particles is as high as 104

m s, still applying the views and laws of classical mechanics; Obviously, "high speed" should be conditionally high speed. The second is the word "general" in "generally not applicable to microscopic particles", which does not absolutize the description of the problem. It shows that classical mechanics can also be applied to microscopic particles under certain conditions.

So, under what conditions is the description of microscopic particles in classical mechanics valid?

Thinking from the above two questions, how should we define the scope of application of classical mechanics in a more specific and comprehensive way?

1. Define the scope of application of classical mechanics from the research object.

Classical mechanics is the study of the mechanical motion of macroscopic objects and does not involve thermal motion and electromagnetic field motion.

"Object" - refers to the physical object, excluding substances such as "field".

In theoretical research, there are also requirements for the structure of the physical object: the object as a whole can be regarded as a particle; Objects are several special groups of particles.

Newton's laws are based on the particle model, and in principle, all particle problems can be solved on the basis of the kinetic equation of the particle. However, due to the complexity of the practical problem and the complexity of the theoretical calculation, only a few special groups of particles can be dealt with: very simple free groups of particles (partial solutions of the two-body problem and three-body problems), and various ideal models of the particle groups (such as rigid bodies, complete elastomers, ideal fluids, ideal infinity media, 、......etc.).

Therefore, the "particle group" is the scope of application in principle of classical mechanics, and the actual scope should be narrowed.

Classical mechanics based on Newton's laws of motion is only suitable for solving low-speed motion problems, not for dealing with high-speed motion problems; It is only suitable for macroscopic objects, and generally not for microscopic particles

Macroscopic low-velocity objects are not suitable for microscopic and high-velocity objects.

a) Newton's third law.

1. Content: The force and reaction force between two objects are always equal in magnitude and opposite in direction, acting in a straight line. The expression is f= f.

2. Characteristics of action and reaction force.

1) The action force and the reaction force are generated at the same time and disappear at the same time.

2) The action force and the reaction force act on the two objects respectively, and each produces an action effect.

3) The action force and the reaction force must be forces of the same nature.

4) The magnitude relationship between the action force and the reaction force has nothing to do with the motion state of the object.

b) Newton's first law.

1. Contents: All objects always maintain a state of uniform linear motion or a state of rest until an external force forces it to change this state.

2. Understanding Newton's first law.

1) When the object is not subjected to force, it is either in a state of uniform linear motion or at rest, that is, the state of motion will not change.

2) The external force is not the cause of maintaining the motion of the object, but the reason for changing the state of motion of the object.

3) The motion state of the object is determined by the velocity of the object, and the change of the motion state of the object is the change of the velocity of the object, that is, the object has acceleration, indicating that the force is the cause of the acceleration.

3. The understanding of inertia (the property of an object that keeps its original uniform straight line or state of rest is called inertia).

1) All objects have inertia, and inertia is an inherent property of objects.

2) Since the difficulty of changing the state of motion is determined by the mass of the object, therefore: mass is a measure of the magnitude of inertia, the inertia of an object with a large mass is large, and the inertia of an object with a small mass is small.

c) Newton's second law.

1. Content: The acceleration of the object is directly proportional to the resultant external force of the object, inversely proportional to the mass of the object, and the direction of acceleration is the same as the direction of the resultant force.

2. Formula: f = ma

3. The understanding of Newton's second law should pay attention to the following points:

1) Since force is the cause of acceleration, an object has acceleration only when it is subjected to force.

2) Acceleration and force are both vector quantities, and the direction of acceleration is determined by the direction of the force, that is, the acceleration and the resultant force are isotropic.

3) The action of force and the generation of acceleration are simultaneous, not in order.

4) Acceleration varies with the change in force. When the external force changes with time, the acceleration also changes with time. When the external force is constant, the acceleration of the object is also constant, and when the external force stops acting, the acceleration disappears immediately and the object remains in motion.

1) The carriage of the brother is affected by the resultant force of the wheel sail f and the frictional force, and it is a constant force hail, so it is regarded as a uniform acceleration motion, x= at, bring in x=5m, t=2s, and the solution is a=

2) The force on the carriage is f=ma=75n

Friction f=f-f=45n ab should be equal in friction.

f=ma aa aa=

v=at=3)x=½at²=

Choose A. The conventional method to solve mechanical problems is to first select the correct research object, analyze the force, and then carry out the orthogonal decomposition of the force in the direction of the imitation of trapped rolling, and establish the corresponding equation by Newton's laws of motion or force equilibrium.

A always remains stationary relative to B, which means that the acceleration and velocity of A and B together are always the same, that is, A also accelerates to the right with a gradual decrease in acceleration, and the residual surface force analysis combined with the motion state can be solved.

a. Force analysis: vertical downward gravity, vertical inclined upward support force and upward static friction along the inclined surface (at this time, there needs to be a horizontal force or component, which should balance the horizontal component of the supporting force and provide horizontal acceleration, so the direction of static friction must be upward along the inclined surface).

acceleration horizontal, then establish a Cartesian coordinate system along the horizontal and vertical lines. In the vertical direction, the sum of the components of the support force and the friction force is equal to the gravitational force, if either of the support force and the friction force increases, the other must decrease, so the answer BC excludes. If the horizontal direction is known, and the acceleration decreases, then d is excluded.