What are the applications of Newton s three laws? How does Newton s third law apply in life?

Newton's first law does not hold true in all frames of reference, only in inertial frames of reference.

Newton's second law The resultant external force on an object will produce acceleration, which may change the motion state or velocity of the object, but this change is related to the motion state of the object itself.

In a vacuum, since there is no air resistance, various objects have the same acceleration regardless of their mass because they are only subjected to gravity. Therefore, in free fall, their velocity changes the same in the same time interval.

Newton's third law (1) There is no priority or order between action and reaction forces. Creates and disappears at the same time.

2) This pair of forces acts on different objects and cannot be counteracted.

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

4) Nothing to do with the frame of reference.

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?

However, in fact, when dealing 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, high school physics textbooks still apply the viewpoints and laws of classical mechanics even if the velocity of the particles reaches 104 -106 m s. 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.

be able to deduce the dark energy of the universe; Ability to derive the principle of energy relativity; Ability to derive the energy of the **; Ability to derive the origin of the movement.

1. Application of Newton's first law.

Because when the bus suddenly brakes sharply and the chain hail, the passenger is still moving forward due to inertia, so when the state suddenly changes, it will fall forward due to the inertia of the shed. In the same way, when the bus starts suddenly, the passenger's state is from stationary to forward, and it will fall backwards because the inertia is still in a stationary state.

2. Application of Newton's second law.

When the football is stationary on the turf, then when a person is playing a football, the football will gain a greater acceleration and the state of motion will change. The greater the force of the person on the football, the greater the acceleration of the football, and the speed of the movement of the football will be faster. Of course, when we pass the ball, the ball will also move obediently in the direction of the person's pass.

In soccer games or training, in fact, the force of the soccer ball is far more than one force from the canopy and the sail, for example, when the continuous passing between players, the soccer itself is subjected to many forces obtained in different directions, then the direction and speed of the soccer ball will change, and there will also be movement in the opposite direction.

For example, when taking a corner kick, the penalty team player throws the ball at a very fast speed and the acceleration is also very large, at this time, the receiving player does not need to change the route of the ball, only needs to touch it lightly, and can shoot towards the goal with the previous acceleration, which is the actual embodiment of Newton's second law.

3. Application of Newton's third law.

In a motor car accident, two cars collide, then the force and reaction force for the two cars are the same, if one car is seriously damaged because of the collision with another car, the other car must also be damaged because of the force.

Newton's third law not only reveals the law of interaction between two objects, but also provides a theoretical basis for solving mechanical problems and converting research objects, broadens the scope of application of Newton's second law, and is an inseparable and important part of Newtonian physics.

1. Content: The force and reaction force between two objects are always equal in magnitude and opposite in direction, acting on the same straight line.

2. A deep understanding of Newton's third law:

1) Newton's third law contains four characteristics and three properties of action and reaction forces.

The four characteristics are: equal size; Reverse; collinear; Homogeneous forces.

The three properties are: mutuality, i.e., the two are always mutual, appearing in pairs. Allogeneity, i.e. the two acting on two different objects that interact with each other, is the main and most obvious difference from a pair of equilibrium forces.

Simultaneity, that is, both come into being, change at the same time, and disappear at the same time.

Note: To change the motion of an object, other objects must interact with it. The interaction between objects is manifested through force.

He also pointed out that the action of force is mutual, and there must be a reaction force. They act on the same straight line, equal in size and opposite in direction.

Also note:

1) There is no priority or priority between action and reaction forces. Creates and disappears at the same time.

2) This pair of forces acts on different objects and cannot be counteracted.

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

4) Nothing to do with the frame of reference.

The action and reaction forces between the two interacting objects are always equal in magnitude and opposite in direction, acting on the same straight line. Newton's third law of motion and the first.

The first and second laws together constitute Newton's laws of motion, which expound the basic laws of motion in classical mechanics.

Newton's first law: It refers to the fact that all objects always remain at rest or in a uniform linear motion when they are not affected by external forces. Also known as the law of inertia.

Newton's second law: The acceleration of an object is directly proportional to the resultant 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 force. f=ma

Newton's third law: A pair of forces acting on two objects, equal in magnitude and in opposite directions, acting on the same straight line, but acting on two different objects.

Newton's first law (law of inertia).

Expression 1: Any object that is not affected by an external force or a balanced force (fnet=0) always remains at rest or in a state of uniform linear motion until an external force acting on it forces it to change this state.

Expression 2: When the particle is far enough away from other particle points, the particle moves in a uniform straight line or remains stationary.

That is, mass is a measure of the magnitude of inertia.

The magnitude of inertia is only related to mass, not to the speed and roughness of the contact surface.

The greater the mass, the greater the work done to overcome inertia; The smaller the mass, the less work done to overcome inertia.

Newton's second law of motion.

The acceleration of an object is directly proportional to the resultant external force experienced by 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.

Formula: f = ma

Unit: n (Niu) or kilogram-meter per second square).

The six properties of Newton's second law.

1) Causality: Force is responsible for the generation of acceleration.

2) Homogeneity: F, M, and A correspond to the same object.

3) Vector: Force and acceleration are both vector quantities, and the direction of acceleration of the object is determined by the direction of the combined external force on the object. Newton's second law mathematical expression f

In ma, the equal sign not only indicates that the left and right sides are equal, but also indicates that the direction is the same, that is, the direction of the acceleration of the object is the same as the direction of the combined external force.

4) Transientness: When the external force on the object (with a certain mass) changes suddenly, the magnitude and direction of the acceleration determined by the force must also change abruptly at the same time; When the resultant external force is zero, the acceleration is zero at the same time, and the acceleration and the resultant external force maintain a one-to-one correspondence. Newton's second law is an instantaneous law that indicates the instantaneous effect of force.

5) Relativity: There is a coordinate system in nature, in which the object will maintain a uniform linear motion or a stationary state when it is not subjected to force, and such a coordinate system is called an inertial reference system. The ground and objects that are stationary or moving in a straight line at a uniform speed relative to the ground can be regarded as inertial frames of reference, and Newton's laws are only true in inertial frames of reference.

6) Independence: Each force acting on the object can independently produce an acceleration, and the sum of the acceleration generated by each force is equal to the acceleration generated by the combined external force.

Scope of application. 1) Only suitable for objects moving at low speed (lower velocity than the speed of light).

2) It only applies to macroscopic objects, Newton's second law does not apply to microscopic atoms.

3) The frame of reference should be an inertial frame.

Newton's third law of motion.

The action and reaction forces between two objects, in the same straight line, are equal in magnitude and opposite in direction. (See Newton's third law of motion for details).

Expression. f=-f'

The Third Law. f denotes the applied force, f'denotes the reaction force, and the minus sign indicates the reaction force f'in the opposite direction of the force f).