"The Force from the Earth" Familiar and Unfamiliar Forces PPT Courseware 2

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"The Force from the Earth" Familiar and Unfamiliar Forces PPT Courseware 2

【Experience】Gravity

Activity 1: Hold the rubber with your hands, let go and then drop it to observe the movement of the rubber.

Activity 2: Throw the rubber upward and observe the movement of the rubber.

The rubber eventually falls to _________.

Tip: Ground

Doubtful about preview

1. How is gravity produced?

2. What is the relationship between the magnitude of gravity and mass?

3. What is the direction of gravity? What are its applications?

4. How to determine the center of gravity of an object?

Exploration 1 Gravity

Consider the following questions based on the activities in "Experience":

1. Why does the rubber always fall to the ground during the experience?

Tip: The movement state of the rubber changed during the movement because it was acted upon by a force. When they all fell back to the ground, they must have been acted upon by a force directed toward the ground. This force is caused by the attraction of the earth, and we call it gravity.

Reference answer: affected by gravity

2. The object exerting force by gravity is _________, and the object receiving force is _________.

Tip: Gravity is the force exerted by the earth's attraction. Its force-exerting object is the earth, and the force-receiving objects are all objects on the ground.

Reference answer: Earth, all objects on the ground

3. Guess what would happen to an object if it lost gravity?

Reference answer: If gravity is lost, all objects will float in the air, people will fly, etc.

Exploration 2 Explore the relationship between the magnitude of gravity (weight of an object) and the mass of the object

1. Measurement of gravity: How to measure the magnitude of gravity?

Reference answer: Hang the object on the hook of the spring dynamometer. When it is stationary in the vertical direction, the indication of the spring dynamometer is equal to the gravity on the object.

2. Experimental design: as shown in the figure

Select multiple hook codes with the same ________, measure the ________ of the hook codes, and analyze the data to find out the relationship between gravity and mass.

Tips: Use hook codes with the same mass to measure their gravity. Since the mass of each hook code is the same, the mass of different numbers of hook codes has a multiple relationship, and the gravity also increases in multiples. It is easy to find the relationship between gravity and mass. .

Reference answer: mass gravity

3. Experimental data and analysis:

What conclusions can be drawn from these data?

Tip: It can be seen from the data in the table that as the mass of the hook code increases, the gravity on the hook code also increases, and the ratio of gravity and mass is always a certain value of 9.8N/kg. It can be concluded that the object is subject to The magnitude of gravity is proportional to mass.

Reference answer: The gravity exerted on an object is proportional to its mass, and the ratio is constant.

Knowledge summary

1. Gravity

1. Concept: The force exerted on objects near the earth due to ___________.

2. Force-exerting object: _____.

2. Three elements of gravity

1. Size:

(1)Measuring tools:___________.

(2) Weight of object: ___________ suffered by the object.

(3)The relationship between weight and quality

①Relationship: The gravity exerted by an object is _____ with its mass, and the ratio is a constant value.

Approximately equal to ________.

②Relationship: G=___, where g=________.

③The meaning of g: __________________.

2. Direction:

(1) Direction: _________.

(2) Application: Use _______ to detect whether the wall is vertical, etc.

3. Center of gravity:

(1)Concept: _______ the gravity exerted by each part.

(2) Position determination: The center of gravity of an object with uniform mass distribution and regular shape is on its ________.

(3)Methods to improve stability

①_____Bottom supporting surface. ②_____center of gravity position.

Test Point 1 Explore the relationship between gravity and mass

[Typical Example 1] (2012 Xiangyang High School Entrance Examination) Students in a physics experiment group are exploring

The experimental record of "The relationship between the gravity of an object and the mass of the object" is as follows:

(1) During the experiment, the measurement tools required are: ______, _____.

(2) According to the experimentally measured data, it can be seen that the ratio of the gravity G on the object to the mass m of the object is ______N/kg.

(3) Analyze the experimental data in the table and draw the conclusion: _______________________________________________.

[Concise Lecture and Analysis] This question examines the relationship between the gravity and mass of an object, averaging multiple measurements to reduce errors, and selecting experimental equipment according to experimental requirements. (1) When exploring the relationship between the gravity on an object and its mass, it is necessary to measure the mass and gravity. The required measurement tools are a balance and a spring dynamometer.

(2)The average value is:

(3) From the data analysis in the table, the ratio of the gravity on the object to its mass remains unchanged, so the gravity on the object is proportional to its mass.

Answer: (1) Balance spring dynamometer (2) 9.8

(3) The gravity experienced by an object is proportional to its mass

[Method summary]

(1) Size measurement: Use a balance to measure the mass of the object, and use a spring dynamometer to measure gravity in the vertical direction.

(2) Analyze data: Compare the ratio between gravity and mass, eliminate experimental errors, and draw conclusions.

1. If there is no gravity on the earth, the following phenomena may occur: ()

A. The primary school student lifted the truck with one hand B. The water of the Yellow River continues to flow

C.Ripe apples fall from the tree D.Throwed stones will fall back to the ground

[Analysis] Choose A. This question tests the understanding of gravity. Gravity is the force generated by the attraction of the earth, and the direction is vertically downward; if there is no gravity, the truck will not be affected by gravity, and primary school students can lift the truck; water will no longer flow from high to low, and apples will not fall to the ground. The stone that goes out will no longer fall back to the ground.

2.g=9.8N/kg, regarding its meaning, the correct one of the following statements is ()

A.The force of 1N is 9.8kg

B.1kg=9.8N

C. An object with a mass of 9.8kg experiences a gravity of 1N.

D. An object with a mass of 1kg experiences a gravity of 9.8N.

[Analysis] Choose D. This question tests your understanding of g=9.8N/kg. The physical meaning of g=9.8N/kg is that an object with a mass of 1kg near the ground experiences a gravity equal to 9.8N.

3. (2012·Wenzhou High School Entrance Examination) In the physical education class, the pushed shot put rolled forward along the horizontal ground after landing (as shown in the picture). The direction of the gravity exerted by the shot put in the picture is ()

[Analysis] Choose C. This question examines the direction of gravity. All objects on the surface of the earth are affected by gravity, regardless of their motion state, and the direction of gravity is vertically downward.

4. As shown in the picture, when traveling and mountaineering, the items in the backpack may be light or heavy. How should they be placed to prevent people from falling backwards easily ()

A. Place heavy items in the lower part of the backpack

B. Place heavy items on the upper part of the backpack

C. Place heavy items in the middle of the backpack

D. You can place it anywhere you like

[Analysis] Choose B. This question tests the understanding and application of center of gravity. When a person is walking, the person's center of gravity is approximately as shown in the figure. In order to prevent the person from falling backward easily, the vertical distance between the heavy objects in the backpack and the person's center of gravity should be the shortest. Heavy objects should be placed on the back. The upper part of the capsule.

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Update Time: 2024-10-01

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