"Newton's First Law of Motion" Newton's Laws of Motion PPT download

"Newton's First Law of Motion" Newton's Laws of Motion PPT download

The first part of the content: [Learning literacy·clear goals]

Physical concepts: 1. Understand the different views and basis of Galileo and Aristotle on the relationship between motion and force. 2. Know Galileo’s ideal experiments and reasoning methods. 3. Understand the content and meaning of Newton’s first law. 4. Know Inertia, and will correctly explain the relevant phenomena.

Newton's first law of motion PPT, part 2: independent preview to explore new knowledge

Knowledge sorting

1. The relationship between force and motion

1. Aristotle's point of view: An object can move only when there is an external force. To maintain the motion of an object, an external force is needed.

2. Galileo's perspective

(1) Ideal experiment (as shown in the picture): The ball rolls down from a certain height on the left side along a smooth slope. No matter what the slope of the right side is, it will rise to a place almost _____ with the starting point.

(2) Conclusion: Maintaining the motion of an object does not require _____.

3. Descartes' point of view: If there is no other reason, the moving object will continue to move in a straight line with the original _____.

4. State of motion: _____ is a physical quantity that describes the state of motion of an object. Changes in the state of motion refer to changes in _____.

5. The relationship between force and motion: Force is not the reason that maintains the motion of an object, but the reason why the object is in motion.

2. Newton’s first law

1. Content: All objects always remain in __________ state or _____ state, unless _____ forces it to change this state.

2. significance

(1) Newton's first law states that when an object is not subject to external forces (or the total external force is zero), the object will maintain its original _____ state or _____ state.

(2) If the object’s motion state remains unchanged, the _____ it receives must be zero; if its motion state changes, it must receive non-zero _____.

3. Inertia of objects

1. Definition: Any object has the property of maintaining a constant _____ or __________ state. In physics, this property of an object is called inertia.

2. Understanding: Inertia is the _____ of an object, and has nothing to do with the force and motion of the object.

3. Determining factor: _____ is the only measure of the inertia of an object. The greater the mass, the more _____ the object's inertia is, and the more difficult it is to change the object's motion state.

Basic self-test

1. Think and judge (mark “√” if correct, “×” if incorrect)

(1) When the speed changes, the motion state of the object changes. ( )

(2) The direction of motion changes, but the motion state of the object remains unchanged. ( )

(3) The object is not subject to external forces, which means that the total external force exerted on the object is equal to zero. ( )

(4) Newton's first law is an experimental law. ( )

(5) Inertia is the essential attribute of an object and has nothing to do with factors other than mass. ( )

(6) Newton's first law explains that force is the cause of changing the motion state of an object. ( )

2. (Multiple choices) In the process of establishing mechanical theory, many great scientists have made contributions. Regarding scientists and their contributions, which of the following statements is correct ()

A. Galileo believed that force was not what kept objects in motion

B． Aristotle believed that the motion of objects does not require force to maintain

C. Newton was the first to point out that force is not what keeps objects moving

D． Galileo believed that force is what changes the state of motion of an object

3. (Multiple choice) Which of the following statements is correct ()

A. Newton's first law was imagined out of thin air by scientists and has no experimental basis.

B． Newton's first law cannot be directly verified experimentally

C. The thinking method of ideal experiment is the same as the thinking method of establishing particle model. They are both scientific and abstract thinking methods.

D． According to Newton's first law, an object at rest must not be acted upon by any external force.

4. Among the following examples, the inertia of the object is used ()

A. Wear seat belts when riding a bus

B． Skydiver opens parachute before landing

C. Bicycle tires have uneven patterns

D． Discus thrower throws discus after rapid spin

Newton's First Law of Motion PPT, Part 3: Collaborative exploration to overcome difficult problems

Understanding Newton's First Law

1. Clarified the concept of inertia

The first half of the law, "All objects always remain at rest or in a state of uniform linear motion", reveals a property universally possessed by all objects - inertia, that is, an object remains at rest or in a state of uniform linear motion. It is an essential attribute and does not require conditions. ． All objects have the property of remaining at rest or moving in a straight line at a uniform speed under any circumstances. Therefore, Newton's first law is also called the law of inertia.

2. Clarify the effect of force

The second half of the law "unless there is an external force forcing it to change this state" shows that the effect of force can change the motion state of an object. The law clearly states that force can change the motion state of an object.

3. Revealed the relationship between force and motion

Newton's first law points out the law of motion of an object when it is not subject to external forces. The law only describes an ideal state. In reality, there is no situation where an object is not subject to external forces. When the total external force on an object is zero, its The effect is the same as that without external force. The relationship between force and motion: Movement does not require force to maintain, but the change of motion state cannot be separated from the action of force.

[Example 1] Which of the following statements about Newton’s first law is correct ()

A. Newton's first law is an experimental law

B． Newton's first law only proposes the concept of inertia

C. Newton's first law states that when the net external force on an object is zero, the object will be at rest.

D． Newton's first law not only proposes the law of motion of an object when it is not acted upon by external forces, but also proposes that force is the cause of changing the state of motion of an object.

Thoughts: When answering this question, you should pay attention to the following three points:

(1) The difference between Newton’s first law and inertia.

(2) The relationship between force and motion.

(3) The relationship between force and changes in motion state.

regular method

Newton's first law describes the state of an object when it is not acted upon by an external force - it always maintains uniform linear motion or a state of rest. It also reveals the relationship between force and motion - force is not what maintains the motion of an object, but changes its state of motion. Reason. When analyzing such problems, we should pay attention to the difference between Newton's first law and inertia.

Understanding and applying inertia

1. The "one", "two existences" and "three differences" of inertial phenomena

(1) "One": The size of inertia is only related to the mass of the object.

(2) "Two Beings": Inertia is an inherent attribute of all objects; objects have inertia under any circumstances.

(3) "Three differences": the difference between inertia and the first law; the difference between inertia and force; the difference between inertia and speed.

2. The relationship between inertia and force

(1) Inertia is not a force, but an inherent property of the object itself. Therefore, it is wrong to say that "the object is affected by inertia", "generates inertia", and "is subjected to inertia force".

(2) Force is what changes the state of motion of an object, and inertia is what maintains the state of motion of an object. The greater the force, the faster the motion state changes; the greater the inertia, the harder it is to change the motion state.

(3) Inertia has nothing to do with the force on the object.

3. The relationship between inertia and speed

(1) Inertia has nothing to do with the state of motion. No matter what state of motion the object is in, inertia always exists. When the object is stationary, it always "wants" to maintain this static state; when the object moves, it always "wants" Make uniform linear motion with the speed at that moment.

(2) All objects have inertia, which has nothing to do with whether the object has speed or the magnitude of the speed.

4. "Two manifestations" of inertia

(1) Without external force, inertia shows "maintaining" the "original" state of motion.

(2) Under force conditions, inertia shows the difficulty of changing the state of motion. The greater the mass, the greater the inertia, and the more difficult it is to change the state of motion.

[Example 2] As shown in the figure is a schematic diagram of a car seat belt control device. When the car is at rest or moving in a straight line at a constant speed, the brake pendulum hangs vertically, the lock rod is horizontal, the ratchet can rotate freely, and the seat belt can be pulled. When the car suddenly brakes, the pendulum swings around the axis due to inertia, causing the lock rod to lock the rotation of the ratchet and the seat belt cannot be pulled. If the pendulum swings from the solid line position to the dotted line position in the figure, the possible motion direction and motion state of the car are ()

A. Driving to the right, moving in a straight line at a constant speed

B． Driving to the left, moving in a straight line at a constant speed

C. Driving to the right, braking suddenly

D． Driving to the left, braking suddenly

regular method

Methods of explaining phenomena using inertia

(1) Clarify the original state of motion of the object under study.

(2) When an external force acts on a certain part of the object (or an external force acts on other objects related to the object), the change in the motion state of this part.

(3) What state of motion the object maintains due to inertia, and determine what phenomenon will occur in the end.

Newton's First Law of Motion PPT, Part 4: Complying with Standards in Class and Solidifying the Double Base

1. Which of the following understandings of exercise is incorrect ()

A. Aristotle believed that the natural state of an object is to be at rest and that it only moves when acted upon by a force

B． Galileo believed that force was not what kept objects in motion

C. Newton believed that the effect of force was to change the speed of an object

D． Galileo deduced based on ideal experiments that if there is no friction, once an object on the horizontal plane has a certain speed, it will keep moving at this speed forever.

A　Motion is a natural property of objects and does not require force to maintain, so item A is wrong and item B is correct. The effect of force is to change the motion state of the object, that is, to change the speed, so item C is correct. If the object is not subject to external force, its motion state does not change, that is, its speed does not change, so item D is correct. ]

2. Among the following situations, there is no need to exert force on the object ()

A. Object changes from rest to motion

B． object changes from motion to rest

C. The direction of motion of an object constantly changes

D． The object's speed and direction of motion do not change

D. The object changes from stationary to moving, and from moving to stationary, indicating that the object's speed changes; the object's direction of motion continues to change, indicating that the object's speed direction changes. Force is what causes the speed of an object to change. Therefore, when the speed of an object changes, it must be affected by a force. So choose D.]

3. Which of the following statements is correct ()

A. An object at rest or moving in a straight line with uniform speed must not be acted upon by external forces

B． Fighters lose their auxiliary fuel tanks before combat to reduce inertia

C. A glass dropped from a high place is more likely to break than a glass dropped from a low place because the former has greater inertia.

D． The ease with which an object's state of motion changes depends on its speed

B [ The object is in a state of rest or in a state of uniform linear motion. It may also be because the net external force it receives is zero. Option A is wrong. In order to improve combat flexibility, fighter jets discard the auxiliary fuel tanks before combat, thereby reducing the mass of the aircraft and reducing the weight of the aircraft. The inertia of a small aircraft increases the maneuverability of the aircraft. Option B is correct; a glass falling from a high place is more likely to break than a glass falling from a low place. This is because the impact force on a glass falling from a high place is greater, so it is easier to break. , the size of the inertia depends on the mass of the glass, option C is wrong; for a moving object, inertia shows the difficulty of changing the state of motion, option D is wrong. ]

4. Among the following statements about inertia, which one is correct ()

A. Wearing seat belts when riding in a car can reduce inertia

B． Spaceships also have inertia in space

C. The slower an athlete runs, the smaller the inertia

D． The car has inertia when it starts

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