Lu Jiao Edition Eighth Grade Physics Volume 2

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"Force and Its Effects" Force and Motion PPT Courseware

Knowledge point 1. Force is the interaction between objects

Experience: Stretch out your hand and hit your classmate. Does your hand feel pain? Does your classmate feel any pain?

Think about it: if you are sitting in a small boat and pushing another small boat hard, can the other boat push your boat away and stop it?

When you feel pain, your classmates will feel pain too. Pushing away another boat will push your boat backwards. This shows that the effects of forces are reciprocal.

1. The concept of understanding:

1. Definition: Force is the effect of one object on another object.

Thinking: Can force be produced without an object?

2. Features:

(1) Force cannot exist without objects.

(2) Force always exists between two objects, one is the object exerting force (the force exerting force is called action force), and the other is the object receiving force (the force generated is called reaction force).

(3) The force between objects is mutual. The object exerting force also receives the force exerted by the object receiving force. The two forces are equal in magnitude and opposite in direction.

3. The unit of force: Newton, referred to as Newton, and the symbol is N.

Enrich your notes

Characteristics of interaction forces (action and reaction):

1. Equal in size and opposite in direction, on the same straight line, but acting on two objects.

2. To be produced at the same time and to be destroyed at the same time.

3. The properties are the same. For example, the force exerted by a child on the wall is a pushing force, and the force exerted by the wall on the child is also a pushing force.

discuss

Does direct contact between two objects necessarily produce a force?

Does it mean that if two objects are not in direct contact, no force will be generated?

in conclusion:

Direct contact between two objects does not necessarily produce a force. But there must be no force without contact, such as: pressure, friction, support, push, pull, etc.

Two objects can produce force without direct contact, such as gravity, magnet force, etc.

create situations

Think about it: Through the following small experiment, can you tell the two types of effects of force?

Observation: What happens when the magnet comes close to the small steel ball?

Phenomenon: When the magnet is close to the small steel ball, the small steel ball starts to move.

Observation: A small steel ball moves at a constant speed on a smooth horizontal surface. If a magnet is placed in a position perpendicular to the direction of motion, what will happen to the movement of the small ball?

Phenomenon: The direction of movement of the ball changes.

Do it: Pull and compress the spring hard to see what happens to the shape (length) of the spring?

Phenomenon: The shape of the spring changes, becoming longer or shorter.

Knowledge point 3. Three elements of force

Think about it: Students review the situation of playing billiards.

Observation: When hitting a billiard ball with different strengths (sizes), the greater the force, the farther the ball moves.

Explanation: The size of the force affects the effect of the force.

Observation: When a billiard ball is hit in different directions with the same strength (size), the billiard ball moves in different directions.

Explanation: The direction of the force affects the effect of the force.

Observation: Push the door with the same amount of force, and the distance of your hand from the door axis is different each time. Different effects of force exerted by hand in different positions.

Answer: The point of action of force affects the effect of force.

The three elements of force: magnitude, direction, and point of action.

Note: If the force acting on an object has different magnitude, direction, and point of action, the effect will be different. They all affect the effect of the force.

Knowledge point 4. Schematic diagram of force

1. Definition: A method of using a line segment with an arrow to represent force.

The length of the line segment represents the magnitude of the force. The arrow at the end of the line segment indicates the direction of the force. The starting or ending point of a line segment represents the point of application of the force.

This research method is the model method

2. How to draw the schematic diagram of force:

1. Determine the force-bearing object and the point of action of the force and the direction of the force.

2. Draw a line segment from the point of action of the force along the direction of the force. The line segment drawn by Li Da should be longer.

3. Mark an arrow at the end of the line segment to indicate the direction of the force.

4. Write the symbol and magnitude of common force near the arrow.

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For more information about the PPT courseware "Force and Motion Force and Its Effect", please click the Force and Motion ppt Force and Its Effect ppt tag.

"Force and Its Effects" Force and Motion PPT Courseware 2:

"Force and Its Effects" Force and Motion PPT Courseware 2 1. Force 1. In physics, pushing, pulling, lifting, pressing, repelling, attracting, etc. between objects are usually summarized as actions. 2. Definition of force: Force is the effect of an object on an object. Symbol F 3. Unit of force: Newton Simple...

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Update Time: 2024-09-30

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