What is the expression of Newton s second law

Newton's second law.

The magnitude of the acceleration of the 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.

Scope of application: 1. Newton's second law of motion only applies to particles. For the particle system, the isolation method is generally used when using Newton's second law of motion, or Newton's second law of the particle system is used.

2. Newton's second law of motion only applies to inertial frames of reference. The inertial frame of reference refers to the frame of reference in which Newton's laws of motion are established, and in non-inertial frames of reference, Newton's second law of motion does not apply. However, through the introduction of inertial forces.

It is possible to make the representation of Newton's second law of motion used in non-inertial frames.

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

Formula: f (resultant force) = ma

Newton's second law of motion, Newton's second law of motion

1. The content of the law: The acceleration of an object is directly proportional to the resultant external force f 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. From the point of view of physics, Newton's second law of motion can also be expressed as "the rate of change of momentum of an object with time is proportional to the sum of the external forces subjected to it".

That is, the first derivative of momentum to time is equal to the sum of external forces.

2 Formula: f = ma

Newton's original formula: f = δ (mv) δt (see Newton's Mathematical Principles of Natural Philosophy).That is, the rate of change of the force is proportional to the momentum of the object, which is also called the momentum theorem.

In the theory of relativity, f=ma is not true because the mass changes with velocity, while f=δ(mv) δt is still used.

3 A few notes:

1) Newton's second law is the law of instantaneous action of force. Force and acceleration are generated, changed, and disappeared at the same time.

2) f=ma is a vector equation, the positive direction should be specified when applying, where the force or acceleration is the same as the positive direction is taken as a positive value, and the negative value is taken otherwise, and the direction of acceleration is generally taken as the positive direction.

3) According to the principle of independent action of forces, when Newton's second law is used to deal with the problem of the motion of an object in a plane, the forces on the object can be orthogonally decomposed[1], and the component form of Newton's second law can be applied in two mutually perpendicular directions: fx=max, fy=may.

4.The six properties of Newton's second law:

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

2) Vectorability: Force and acceleration are both vector quantities, and the direction of the acceleration of the object is determined by the direction of the external force on the nucleus of the object. In the mathematical expression of Newton's second law f = ma, the equal sign not only indicates that the left and right sides are equal in value, 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.

3) 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 should 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.

4) 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.

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

6) Identity: A and F correspond to a certain state of the same object.

Zhuyin one one one

Pinyin niú dùn dì èr dìng lǜThe basic definition is badOne of the important laws in mechanics. Under the action of external forces, the object will change the state of motion and gain acceleration. The magnitude of acceleration is directly proportional to the external force experienced by the object and inversely proportional to the mass of the object.

The direction of acceleration is the same as that of the external force.

Categories: Education Academic Exams >> Gaokao.

Analysis: Key Points of Knowledge].

1.Changes in motor status:

A change in motion is essentially a change in velocity, and it includes two cases: It is the magnitude of the velocity.

A change is a change in the direction of movement.

2.Newton's Second Law:

The acceleration of an object is directly proportional to the resultant force of the external force and inversely proportional to the mass of the object, the direction of acceleration.

It is the same as the direction of the resultant external force.

Formula: f-mas

Force is what changes the state of motion of an object. Because there is force that produces acceleration.

The rule of 1n: The force that causes an object with a mass of 1 kg to produce an acceleration of 1m s2 is 1n.

1n=1kg·m/s2

Before Newton's unit was defined, Newton's second law was expressed as f=kma) Acceleration is a vector quantity, and its direction is the same as that of the resultant external force.

3.Equilibrium state: The state in which the object is at rest or in a uniform linear motion is called the equilibrium state.

Equilibrium of forces: The object is in equilibrium under the action of several forces, then this situation is called the equilibrium of forces.

Analysis of key and difficult points].

The combined force is responsible for the occurrence of acceleration. Its magnitude is determined by the f and mass of the object m in Newton's second law, and f is the force on which the object is subjected, not a certain force. For example, "a thing."

The body is still on the level ground, and it is lifted vigorously, without lifting". The f in this example is just.

A pulling force, not a resultant force in Newton's laws. So the force f that is usually said is not the same as.

The resultant external force of the object.

The direction of acceleration is determined by the direction of the resultant external force. It sums up the same direction as the external force.

Newton's second law is the key to the problem of dynamics and must be taken seriously.

2.The relationship between the combined external force, acceleration and the velocity of the object:

When the direction of the resultant external force on the object is the same as the direction of motion of the object, the object moves at an accelerated pace.

When the resultant external force gradually decreases, the acceleration gradually decreases, but the velocity increases.

When the direction of the resultant external force on the object is opposite to the direction of the object's motion, the object moves with deceleration.

No matter how much the acceleration is, the velocity of the object always decreases.

3.Solution ideas:

To solve a problem using Newton's second law, you first need to draw a simple figure of an object.

Correctly analyze the forces on an object. (When there is a resultant force and a component force, the analysis of the resultant force does not analyze its division.)

force, the analysis of the molecule does not say its resultant force. For example, in the upper right diagram, the object is described as a "sliding force".

And "pressure" does not say "gravity", and "gravity" does not say "sliding force" and "pressure".

4.When the result of solving the problem is a negative value for drag or acceleration, be sure to pay attention to the direction when answering. Compare.

For example, if a=-5m s2, you should answer: "The acceleration of the object is 5m s2, and the object is moving in a deceleration motion."

or in the opposite direction to the direction of motion of the object).