"Newton's Second Law of Motion" Newton's Laws of Motion PPT teaching courseware

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"Newton's Second Law of Motion" Newton's Laws of Motion PPT teaching courseware

Part 1: Essential knowledge and foundation of literacy

1. Newton’s second law

1. Content: The acceleration of an object is directly proportional to the _______ it receives, _____ to its mass, and the direction of acceleration is _____ to the direction of the force.

2. Formula: F=____, F refers to the total external force on the object; when the units of each physical quantity are taken as SI units, k=1, F=ma.

3. The international unit of force: Newton, abbreviated as ___, symbol N. The definition of "1 Newton": The force that causes an object with a mass of 1 kg to produce an acceleration of 1 m/s2 is called 1 N.

2. The relationship between the combined external force, acceleration and speed

1. Force and acceleration are causally related: force is the cause and acceleration is the effect. As long as the net external force on the object is not zero, acceleration will occur. The direction of the acceleration and the net external force is _____, and the magnitude and the net external force are _____.

2. There is no causal relationship between force and speed: the direction of the combined external force and speed can be the same or opposite. When the combined external force and speed are _____, the object will accelerate and when _____, the object will decelerate.

3. The difference between a= and a=: a= is the definition of acceleration, which is a physical quantity defined by the _____ method. a, v, Δv, and Δt are all _____; and a= is the determinant of acceleration, and acceleration is determined by Determined by the combined external force and mass.

Newton's Second Law of Motion PPT, Part 2: Key Abilities·Quality Formation

1. Understanding Newton’s Second Law

1. Scope of application of Newton’s second law:

Suitable for inertial reference frames and macroscopic objects

2. The "four properties" of Newton's second law:

(1) Instantaneousness: a and F are generated at the same time, change at the same time, and disappear at the same time, which is an instantaneous correspondence;

(2) Vector property: F=ma is a vector expression. The direction of a at any moment is consistent with the direction of the resultant external force. When the direction of the resultant external force changes, the direction of a changes at the same time, that is, the directions of a and F are consistent at any moment. same;

(3) Homogeneity: Each physical quantity in the formula F=ma refers to the same object;

(4) Independence: When an object is acted upon by several forces at the same time, each force satisfies F=ma, and each force will produce an acceleration. The vector sum of these accelerations is the acceleration of the object.

【Think·Discussion】

According to Newton's second law, acceleration can be generated as long as there is force. A car is parked on the ground.

You can't make the car accelerate even if you try your best. Does this contradict Newton's second law? Why? (physical concept)

[Typical example demonstration]

The following understanding of the expression F=ma of Newton’s second law and its deformation formula is correct ()

A. From F=ma, we can know that the net external force on an object is proportional to the mass of the object and proportional to the acceleration of the object.

B. From m=, it can be seen that the mass of an object is directly proportional to the combined external force it experiences and inversely proportional to the acceleration of its motion.

C. It can be seen from a= that the acceleration of an object is directly proportional to the combined external force it experiences and inversely proportional to its mass.

D. From m=, it can be seen that the mass of an object can be found by measuring its acceleration and the pulling force it experiences.

【Literacy Training】

1. (Multiple choice) What is the correct understanding of Newton’s second law? ()

A. If an object is acted upon by two forces at the same time, the accelerations produced by the two forces do not affect each other.

B. If an object is acted upon by several forces at the same time, the acceleration of the object is equal to the vector sum of the accelerations produced by the forces acting alone on the object.

C. When the combined external force on an object changes suddenly, the acceleration of the object may not change.

D. The mass of an object is directly proportional to the resultant force on the object and inversely proportional to the acceleration of the object.

[Analysis] Choose A or B. According to the independence of Newton's second law, if an object is acted upon by two forces, the two accelerations will not affect each other, and A is correct; according to the correspondence of Newton's second law, if an object is acted upon by several forces, action, then the resultant acceleration is equal to the acceleration produced by the resultant force, the resultant force is equal to the vector sum of each force, each force will produce acceleration, the resultant acceleration is equal to the vector sum of the acceleration produced by each force acting alone on the object, B is correct; according to Newton's The instantaneous nature of the second law shows that when the combined external force on an object changes, the acceleration of the object will definitely change, error C; the mass of an object is the amount of material that makes up the object, and has nothing to do with the force and motion state of the object, error D. Therefore, choose A and B.

2. Simple application of Newton’s second law

1. Problem solving steps:

(1) Determine the research object.

(2) Carry out force analysis and motion analysis, and make force and motion diagrams.

(3) Find the total external force F or acceleration a.

(4) Solve according to the F=ma series of equations.

2. Problem solving method:

(1) Vector synthesis method: The object only experiences two forces, and the parallelogram rule is applied to solve for the resultant force of the two forces. The direction of acceleration is the same as the direction of the resultant force;

(2) Orthogonal decomposition method: When an object is subject to multiple forces, the orthogonal decomposition method is often used to find the resultant external force of the object.

【Think·Discussion】

The worker uses a horizontal thrust of F to push a flatbed truck with mass M. The flatbed truck is loaded with goods of mass m. The goods and the flatbed truck remain relatively stationary. The resistance encountered by the flatbed truck during its movement is always 0.2 times the "vehicle weight". How to solve What is the acceleration of the flatbed truck and the friction between the flatbed truck and the cargo? (scientific thinking)

Tips: The two are relatively stationary and have a common acceleration. Take the whole as the research object, find the overall resultant force through force analysis, divide it by the overall mass, and get the overall acceleration, which is also the acceleration of the flatbed truck; multiply the mass of the cargo by the acceleration of the cargo to get The total external force on the cargo is equal to the friction between the flatbed truck and the cargo, so the solution is solved.

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Update Time: 2024-10-03

This template belongs to Physics courseware Lu Ke Edition High School Physics Compulsory Course One industry PPT template

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