"How to describe force" Familiar and unfamiliar force PPT courseware

Description

"How to describe force" Familiar and unfamiliar force PPT courseware

【Experience】Pull and push

Activities: Try doing the following activities and observe the difference in effects.

Activity 1: Stretch the rubber band with different forces as shown in Figure A.

Activity 2: Use the same force to press and pull the spring as shown in Figure B.

Activity 3: Use the same force to push points A and B on the door as shown in Figure C.

(1) When pulling a rubber band, the greater the force used, the length of the rubber band will change _________.

(2) If the spring is pressed and pulled with the same force, the deformation of the spring will be _____.

(3) Use two forces of the same magnitude to push point A near the door axis and point B on the edge of the door respectively. It will be easier to close the door when pushing ________.

Tips: (1) Longer (2) Different (3) Point B on the edge of the door

Doubtful about preview

1.What are the three elements of force?

2.What is the unit of force?

3. How to represent force in the schematic diagram of force?

Explore 1 The three elements of power

Combined with "experience", think about the following questions

1. In activity 1, the same rubber band stretches differently when pulled with different forces to illustrate the effect of __________ influence. Please give another example.

Reference answer: Amount of force A child and an adult lift the same bucket of water. The child cannot lift the bucket, but the adult can lift the bucket.

2. In activity 2, use the same force to press and pull the spring. The deformation of the spring is different, which illustrates the effect of ________ influence. Let’s give another example.

Tip: In Activity 2, the magnitude and point of action of the force are the same but the direction of the force is different. The deformation of the spring is different, that is, the effect of the force is different. Explain that the effect of force is related to the direction of force.

Reference answer: Direction of force: Push the car forward with the same amount of force, and the car will move forward; push the car backward, and the car will move backward.

3. In activity 3, the magnitude and direction of the force are the same, but the effect of pushing the door is different, which illustrates the effect of _________ influence. Please give another example.

Reference answer: Point of action of the force: Push the lower part of the table with a horizontal force, and the table slides; push the upper part of the table with the same horizontal force, and the table topples.

Explore 2 units of force

Combined with the preview, complete the following fill in the blanks.

(1) The traction force of a large tractor is about ________N;

(2) The force required to hold up two eggs is about ________N;

(3) The force of ants pulling and transporting leaves is about ________N;

(4) The strength to carry 50kg of fertilizer is about ________N;

(5) The thrust of the Long March launch vehicle is about ________N.

Tip: Fill in the numbers with reference to life experience and information introduction.

Reference answer: (1)3×104　(2)1　(3)10-3　(4)500　(5)6×106

Explore 3 force diagrams

Consider the following questions in conjunction with the “experience” activities.

1. Observe the schematic diagram of the cup being subjected to a force of 2N (as shown in the figure), and understand how to draw the schematic diagram of force.

(1) Use a ________ to represent the point of action of the force;

(2) Taking the action point of the force as the starting point, draw a ________ along the direction of the force, and draw ________ at the end of the line segment to indicate the direction of the force;

(3) The _________ of the line segment represents the magnitude of the force.

Tips: Find the three elements of force (magnitude, direction, and point of action) of force from the diagram, and observe how it is expressed.

Reference answers: (1) point (2) line segment arrow (3) length

2. Push point A on the edge of the door with a force of 5N as shown in the figure. Please make a schematic diagram of this force.

Tip: Make sure the force-bearing object is a door, and the point of action is on the edge of the door. Draw a line segment with an arrow along the direction of the force, and draw an arrow at the end of the line segment to indicate the direction of the force. Label the nature and magnitude of the force next to the arrow.

Reference answer:

Knowledge summary

1. Three elements of force

The _____, _____, _______ of force influence the effect of force. The three elements of force are different, and the effect of force is _____.

2. Unit of force

1. Basic unit: _____, abbreviated as ___, symbol __.

2. Size: The force required to lift two eggs is approximately ___.

3. Schematic diagram of force

1. Schematic diagram of force: Draw a _________ on the _____ object along the direction of ___, and mark the ______ of the force to indicate the force exerted on the object in this direction.

2. Representation of force:

(1) The point of action of the force is drawn on _______.

(2)The arrow represents _____ of force.

(3) The _____ (symbol) of force is marked at the end of the arrow.

Test point 1 Three factors for judging the effect of influence

[Typical Example 1] (2012·Jingzhou High School Entrance Examination) After class, a student pushed the lower part of the desk hard, and the desk would slide along the ground; while pushing the upper part of the desk, the desk may overturn, which illustrates the role of force. Effect()

A.Related to the size of the force B.Related to the point of action of the force

C. Relevant to the direction of the force D. Relevant to the force-bearing area

[Idea Guide] The key to solving the problem: analyze the three elements of force exerted and the resulting effects.

【Exquisite analysis】Choose B. This question examines the factors that influence the effect of influence. The effect of force is related to the size, direction and point of action of the force. When the upper and lower parts of the desk are pushed respectively, the point of action of the force is different, and the motion state of the desk is different, the effect of the force is different. Therefore, it shows that the point of action of the force affects The effect of force. So choose B.

Test point 2: How to draw the schematic diagram of force

[Typical Example 2] (2012·Chongqing High School Entrance Examination) As shown in the picture, Xiao Ming pulls a car. Please draw a schematic diagram of the pulling force of the rope on the car. (The action point A of the force has been drawn)

[Concise Lecture and Analysis] Schematic diagram of this question's power test. In this question, the action point of the pulling force of the rope on the car is at point A, the direction is to the right along the direction of the rope, and the magnitude is represented by F.

Answer: As shown in the picture

[Method summary] Steps to draw a schematic diagram of force

That is: a certain point, two lines, three arrows, and four sizes (symbols).

1. On the football field, when an excellent athlete kicks the ball in the right position, the ball will fly past the goalkeeper in an arc and enter the goal. This is the so-called "banana ball". The "proper position" here refers to the () of force based on the analysis of the three elements of force.

A. Size B. Direction C. Point of action D. All of the above

[Analysis] Choose C. This question examines the impact of the three elements of force on the effect of force. The ball will fly past the goalkeeper in an arc and enter the goal because the impact point of the ball is different, the ball movement path is different, and the effects are different. So choose C.

2. Which of the following objects is lifted with a force closest to 3N()

A. A calf B. Two eggs

C. Eighth grade physics textbook D. Two 1 yuan coins

[Analysis] Choose C. This question tests students' estimation ability. The force used to hold up two eggs is about 1N, 3N is equivalent to the force to hold up 6 eggs, B is wrong; the force to hold up a calf is much greater than the force to hold up 6 eggs, A is wrong; to hold up two coins The force of holding up an eighth-grade physics textbook is less than the force of holding up an egg, D is wrong; the force of holding up an eighth-grade physics textbook is equivalent to the force of holding up 6 eggs, C is correct.

3. An object placed on the horizontal ground is subject to a pulling force F. The magnitude of F is 15N. The direction of F forms an angle of 30° with the horizontal direction and is inclined to the upper right. Among the various representation methods in the figure, the correct one is ()

[Analysis] Choose D. This question examines how to draw a schematic diagram of force. A force diagram provides a visual representation of force. The point of action is the starting point of the line segment, the direction of the arrow is the direction of the force, and the magnitude must be marked directly. Only option D is correct.

4. When using a wooden stick to pry a stone, it is easier to pry up the stone by holding the end of the wooden stick than holding it in the middle. This shows that the _______ of force is different and the effect of force is different.

[Analysis] This question examines the three elements of power. The position of holding the stick is different, the point of action of the force is different, and the effect of the generated force is different, which means that the point of action of the force is different, and the effect of the force is different.

Answer: point of action

Find out where you tend to go wrong?

Xiaogang is at point A and pulls the car horizontally to the right with a force of 10N. Please draw a schematic diagram of this pulling force.

[Students’ own answers]

[Teacher Comments]

①Correct: The magnitude of the force is drawn in the force diagram.

②Error: In the force diagram, no arrow is drawn to indicate the direction of the force.

③Error: The action point of the force is missing.

【Correct drawing】

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"How to describe force" Familiar and unfamiliar force PPT courseware 2:

"How to Describe Force" Familiar and Unfamiliar Force PPT Courseware 2 Review: What is force? What effect will force have? What factors are related to the effect of force? The size of the force can affect the effect of the force. The direction of a force can affect its effect. ..

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Update Time: 2024-07-06

This template belongs to Physics courseware Shanghai Science Edition 8th Grade Physics industry PPT template

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