"Force" Familiar and unfamiliar force PPT courseware

Description

"Force" Familiar and unfamiliar force PPT courseware

[experience] sensibility

Activities: Pull, push, lift, and press some objects, and observe changes in the shape or motion of the objects.

Activity 1: Stretch the spring as shown.

Activity 2: The person pushes the table hard to make it move.

Activity 3: Lift the schoolbag upwards with force and feel the feeling of your hands.

Activity 4: Use a magnet to approach the nail as shown in the picture.

(1) When the spring is pulled hard, the length of the spring becomes _______.

(2) What is the reason why the table changes from stationary to moving?

(3) When carrying a school bag, the hand exerts an upward force on the bag, and the hand feels a force in the direction of _______.

(4) The magnet is close to the iron nail. Before the magnet touches the iron nail, the iron nail is _________.

Tips: (1) Long (2) People push against the table. (3) mention (4) attract

pre-study questions

1.What is force?

2. What are the characteristics of force?

3. What are the effects of force?

Explore 1 What is force?

Combined with "experience", think about the following questions:

1. Analyze the activities of pulling springs, pushing tables, carrying school bags, and magnets attracting nails:

(1) What characteristics do they have in common?

(2) From these examples it can be concluded that force is the function of __________.

Tip: These phenomena all involve the action of "force" and involve two objects, one is the object exerting force and the other is the object receiving force. From this, it can be concluded that force is the effect of one object on another object.

Reference answers: (1) Both involve the action of "force"; both involve two objects. (2) One object versus another object

2. Through "experience", think: Can only one object produce force?

Tip: No, force is the effect of an object on an object. Any force phenomenon always involves two objects, one is the object exerting the force, and the other is the object receiving the force.

Reference answer: No.

3. In activity 4, when the magnet attracts the iron nail, there is no contact between the magnet and the iron nail. This shows what?

Reference answer: Objects that are not in contact can also produce force.

Exploration 2 The effects of forces are mutual

Combined with "experience", think about the following questions:

1. Analyze the following examples and discuss what are the characteristics of the role of force?

(a) When the hand hits the table, the hand exerts a force on the table, and the table also exerts a force on the hand;

(b) The left hand slaps the right hand, the left hand exerts a force on the right hand, and the right hand also exerts a force on the left hand;

(c) The hand pulls the rubber band, and the rubber band also pulls the hand;

(d) Lift the schoolbag with your hand upward, and pull the schoolbag downward with your hand;

(e) As shown in the figure, spring A pulls spring B, spring B stretches, and spring A also stretches.

Tip: It can be seen from (a) (b) (c) (d) that when the hand exerts force on other objects, it also receives force from other objects. The hand is both a force-exerting object and a force-receiving object; from (e), we can see that when spring A exerts force on spring B, it is also pulled by B, so both springs stretch. Summarizing the above examples, we can conclude that the role of force is mutual.

Reference answer: The effects of forces are mutual.

2. We often use "an egg hits a stone" to describe the disparity in power between the two opposing sides. The egg (the weak one) can easily be "broken and bloody" while the stone (the strong one) is intact. Can this phenomenon explain the "egg hitting the stone"? When you hit a rock, only the egg receives force but not the stone? Why does this phenomenon occur?

Tips: Answer from the perspective that the forces between objects are reciprocal and the bearing capacity of stones and eggs.

Reference answer: No. In the process of "the egg hits the stone", the egg is subject to the force exerted by the stone on it. The force effects are mutual, and the stone is also affected by the force exerted on it by the egg. However, the endurance capacity of the egg is much lower than that of the stone, so the egg breaks and the stone breaks. Not broken.

Knowledge summary

1. What is force?

1. Concept: Force is the function of ____________________.

2. Characteristics: The action of force must involve two objects, namely _____ object and _____ object.

2. The effects of forces are mutual

1. When object A exerts force on object B, object B also exerts force on object A. Therefore, the effect of force is _____.

2. Force cannot exist without _____. Since the effects of forces are mutual, the object exerting force is also a _____ object.

3. Effect of force

1. Force can cause objects to _____.

2. Force can change the _________ of an object. Changes in the state of motion include changes in the object's speed from ___ to ___, from ___ to ___, and speed _____ or _____.

Test point 1: Reciprocity of force

[Typical Example 1] (2012 Jining High School Entrance Examination) High jumpers always push downward when taking off.

The physics knowledge used is ____________________________.

[Guidance of Thoughts] The key to answering this question is to analyze the changes in the before and after state of the object.

[Concise Lecture and Analysis] This question examines the reciprocity of the effects of forces. When a high jumper pushes hard on the ground, the ground gives the athlete a force in the opposite direction. This force makes the athlete jump upward. This is based on the fact that "the effects of forces between objects are mutual."

Answer: The effects of forces are mutual

[Method Summary] Utilization of the reciprocity of force

Test point 2 The effect of force

[Typical Example 2] (2012·Changchun High School Entrance Examination) Dumplings are one of the traditional Chinese delicacies. The process of making, cooking and eating contains a lot of knowledge: when making dumplings, roll the dough into dough, which shows that force can change the shape of objects_ _______.

[Idea Guide] Key to solving the problem:

(1) Rolling: The dough is acted upon by force.

(2) The dough becomes dough: the shape of the dough changes.

[Concise Lecture and Analysis] This question examines the effect of force. When making dumplings, the dough is rolled into a dough. The dough is acted upon by force and the shape of the dough changes, indicating that force can change the shape of an object.

Answer: shape

1. When force occurs, which of the following statements is correct ()

A. There can be no force-exerting object and force-receiving object at the same time

B. As long as there is a force-receiving object, there is no need for a force-exerting object.

C. As long as there is a force-exerting object, there can be no force-receiving object

D. There must be both a force-receiving object and a force-exerting object. Without the object, there is no function and there is no force.

[Analysis] Choose D. This question tests the understanding of force. This question will be analyzed from the concept of force. Force is the effect of an object on an object. When a force acts, the force-exerting object and the force-receiving object always appear at the same time. The concept of force emphasizes the object on the object, which means that when the force appears, there cannot be only one object, and it is impossible to talk without the object. A powerful presence.

2. Use a rope to lift a bucket filled with water from a well. You will feel a downward force on your hand. The object exerting this force is ()

A. Earth B. Bucket C. Rope D. Water

[Analysis] Choose C. This question tests the understanding of force. Use a rope to lift a bucket filled with water so that the rope is in contact with your hands. The hand exerts an upward pull on the rope, and the rope exerts a downward pull on the hand. The object exerting a downward force on the hand is the rope.

3. Among the four paintings shown in the picture, the one that vividly embodies the rule that "the effects of forces between objects are mutual" is ()

[Analysis] Choose D. This question examines the functional characteristics of force. In item D, two skating students can move in opposite directions as long as one student pushes the other. Since the forces between objects are mutual, when one student pushes the other, the other student will move in the opposite direction. Another student has a force acting on him and is also receiving a reaction force from another student, so he will also move backwards; force A makes the ball move, and the force changes the motion state of the object; items B and C are both Force changes the shape of an object.

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For more information about the PPT courseware "Force Familiar and Unfamiliar", please click on the Force PPT Familiar and Unfamiliar Force PPT tag.

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Update Time: 2024-09-08

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