"Newton's First Law of Inertia" Force and Motion PPT Courseware

Description

"Newton's First Law of Inertia" Force and Motion PPT Courseware

Summary of knowledge points and course standard requirements

1. Thoroughly understand Newton's first law, and be able to know the state of motion from the state of force, or the state of force from the state of motion.

2. Understand the concept of inertia, use inertia knowledge to explain phenomena, and judge changes in the state of objects based on inertia.

The first question is about the establishment process and significance of Newton’s first law.

The focus of the debate: Does force maintain the motion of an object, or change the state of motion of the object?

Experimental exploration: Try to compare the differences in the movement of the car on three planes.

Analysis and argumentation

① In the three experiments, the car finally stopped. Why?

②The distance the car moves in the three experiments is different. What does this mean?

③What is the relationship between the length of the car's movement and the resistance it encounters?

④ If the resistance encountered when the car is moving is further reduced, will the distance of the car move longer or shorter?

Newton's first law is one of the three laws of mechanics and plays an extremely important role in physical science. To master this law, you need to understand the following points:

Understanding 1: "All objects" in the law indicates that this law is universally applicable to all macroscopic objects, whether solid, liquid, or gas

Understanding 2: "No external force" in the law is the condition for the law to be established. But in fact, this is an ideal condition. There is no object that is not affected by any external force. Especially objects on the earth are affected by gravity. In Galileo's experiment, neither the object nor the horizontal surface can be absolutely smooth, even in today's highly developed science and technology. It's impossible to do it, sometimes it's just that the naked eye can't tell the difference, so it's just an ideal experiment. Therefore, this law is derived using abstract thinking and logical reasoning, and its correctness has been proven by numerous experiments and practices.

Understanding 3: The word "or" in the law "always maintains uniform linear motion or resting state" means that the two states must be in one of them and will not exist at the same time. That is to say, when no external force is applied, the originally stationary object remains at rest. The originally moving object will maintain uniform linear motion.

Understanding 4: Objects have inertia and have the property of maintaining their original state of motion. Therefore, Newton's first law reveals: To change the state of motion of an object, a force must be applied. From stillness to motion, from motion to stillness, from slow to fast, from fast to slow, or turning or changing direction, all require strong force. It can be seen that the essence of Newton's first law is to explain that force is the cause of changing the state of motion of an object.

Example 1: If a person jumps straight up while standing in a train moving at a constant speed, where will he land at the starting point?

Analysis: Passengers on the train have the same speed as the train. When the passenger jumps up, there is no force acting on the person in the direction of the train, so the person still maintains the original speed in the direction of the train, so he falls back to original place,

Example 2: The bus turns off the accelerator 10 meters before entering the station;

Shake your hands vigorously to shake off the water on your hands;

After the astronauts get out of the spacecraft, they can still move forward side by side with the spacecraft and will not fall behind the spacecraft.

Class exercises

1. A passenger sitting in a moving car suddenly falls to the right, indicating that the car is in ( )

A. Speed ​​up B. Slow down C. Turn left D. Turn right

2. The reason why the bullet can continue to move after being ejected from the barrel is ( )

A. The bullet is pushed forward

B. The bullet is affected by inertia force

C. Bullets have inertia

D. The inertia of the bullet is greater than the resistance it experiences

3. The shot put is thrown from the athlete's hand and flies in the air. If the earth's gravity disappears at this moment (air resistance is not taken into account), then the shot put will ( )

A. Stop immediately B. Stop slowly

C. Still doing curved motion D. Making uniform linear motion

Summary: When solving problems related to inertia phenomena, the following points should be noted:

(1) Determine the research object;

(2) What state of motion the object was originally in;

(3) The object will change its original state of motion due to the action of external force. If it is not acted upon by external force, it will maintain its original state of motion;

9. Regarding inertia, which of the following statements is correct ( )

A. It is not easy to push an object when it is at rest, so the object has greater inertia when it is at rest than when it is moving.

B. It is difficult for an object to stop when it is moving at high speed, so the greater the speed of the object, the greater the inertia.

C. When an object is not acted upon by a force, it can maintain uniform linear motion or a stationary state, so an object has inertia only when it is not acted upon by a force.

D. Inertia is an inherent property of an object. Any object has inertia under any circumstances.

10. Which of the following statements about Newton’s first law is correct ( )

A. Newton's first law is based on experiments, so it can be directly verified by experiments.

B． The condition that an object is not affected by external forces proposed in Newton's first law is impossible to achieve, so this law may be wrong.

C. Newton's first law is the research result of Newton alone

D． Newton's first law is summarized through further reasoning based on a large number of experimental facts.

11. Under what circumstances did the phenomena shown in A and B in the figure occur ( )

A. It all happens when the car suddenly stops.

B. It all happens when the car suddenly pulls

C. The phenomenon shown in picture B occurs when the car suddenly stops.

D. The phenomenon shown in Figure A occurs when the car suddenly stops.

13. Ideal experiment is an important way of thinking for studying physical laws. It is based on a large number of reliable facts, uses real experiments as prototypes, and derives physical laws through reasonable reasoning. Ideal experiments can profoundly reveal the nature of physical laws.

As shown in the figure, it is Galileo's famous ideal experiment on an inclined plane. The steps envisioned in the experiment are:

① Reduce the inclination angle of the second inclined plane, and the ball still has to reach its original height on this inclined plane.

② Two butt inclined planes, let the stationary ball roll down one inclined plane, and the ball will roll up the other inclined plane.

③ Continue to reduce the inclination angle of the second inclined plane until it becomes a horizontal plane. The ball will continue to move at a constant speed along the horizontal plane.

④ If there is no friction, the ball will rise to the original height when it was released.

(1) Please arrange the above steps in the correct order___________ (just fill in the serial number).

(2) Among the above assumptions, some are reliable facts, while others are idealized inferences. Which of the following classifications of these facts and inferences is correct ( )

A. ① is a fact, ② ③ ④ is an inference

B.② is a fact, ① ③ ④ is an inference

C.③ is a fact, ① ② ④ is an inference

D. ④ is a fact, ① ② ③ is an inference

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Update Time: 2024-10-03

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