"Friction" Motion and Force PPT Courseware 6

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"Friction" Motion and Force PPT Courseware 6

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When the cup is held at rest as shown in the figure, what force is exerted on the cup?

The cup is subject to vertical downward gravity and is stationary. According to the two-force balance condition, the cup is also subject to a vertical upward force exerted by a hand. This force is friction.

1. Friction

1. Definition: When two objects in contact with each other move relative to each other or have a tendency to move relative to each other, a force will be generated on the contact surface that hinders the relative movement or tendency of relative movement. This force is called friction.

2. Conditions for generating friction:

(1) Two objects are in contact with each other and squeeze each other

(2) There is relative movement or a tendency of relative movement

(3) The contact surface is rough

3. The action point of friction: on the two contact surfaces

4. The direction of friction: opposite to the direction of relative motion (or relative motion trend). It cannot be said to be opposite to the direction of object movement.

Notice:

① Relative refers to the relative contact surface

②The relative movement trend can be judged by the hypothetical smooth method

2. Static friction

1. Definition: Two objects that are in contact with each other and remain relatively stationary. When there is a tendency of relative motion between them, a force will be generated on their contact surface that hinders the relative motion between the objects.

2. Conditions for production:

(1) Contact

(2) The contact surface is rough

(3) There is extrusion (deformation) on the contact surface

(4) There is a relative movement tendency between two objects

3. Three elements of static friction

(1) The direction of static friction: along the contact surface and opposite to the direction of the relative motion of the object.

(2) The action point of the force is on the contact surface

Summary of the characteristics of static friction:

(1) The static friction force is analyzed based on the law of two-force balance.

(2) Static friction changes with the change of the external force that produces the tendency of motion, and is always a pair of balancing forces with the external force that causes the object to move relative to the object.

(3) Static friction has nothing to do with the pressure on the contact surface between objects. The maximum static friction force is related to the pressure between objects, the material and roughness of the contact surface.

(4) The direction of the static friction force along the contact surface is opposite to the relative movement trend and is not necessarily opposite to the direction of movement.

friction in life

1. When writing with a pencil, the friction between the pencil tip and the paper

2. When sharpening a pencil with a knife, the friction between the pencil and the knife

3. When the hand slides on the table, the friction between the hand and the table

4. When erasing the blackboard with a blackboard eraser, the friction between the blackboard eraser and the blackboard

5. Push and pull the table on the ground.

6. When holding an object, the friction between the hand and the object

Classroom training

1. For two objects in contact with each other, which of the following statements is correct:

A. If there is elasticity, there must be friction.

B. Elasticity does not necessarily mean friction

C. If there is friction, there must be elasticity.

D. Friction does not necessarily mean elasticity

2. Which of the following statements is correct ( )

A. A moving object must be subject to sliding friction

B. A stationary object cannot be subject to sliding friction.

C. The direction of sliding friction must be opposite to the relative sliding direction.

D. The direction of sliding friction must be opposite to the direction of motion.

3. A wooden box weighs 100N and is placed on a level ground. The kinetic friction coefficient between the wooden box and the ground is 0.2. When a force of 80N is used to push the wooden box, the following statement is correct:

A. Without knowing the maximum static friction force, it is impossible to judge whether it is moving or not.

B. The friction force is static friction force, the size is 80N

C. The friction force is sliding friction force, the size is 80N

D. The friction force is sliding friction force, the size is 20N

judge right or not

①A stationary object may be subject to sliding friction;

② Moving objects may be subject to static friction;

③The direction of sliding friction may be the same as the direction of motion;

④The direction of sliding friction may be opposite to the direction of motion;

⑤Sliding friction is directly proportional to gravity.

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"Friction" interaction PPT download:

"Friction" Interaction PPT Download Part One Content: [Learning Literacy and Objectives] Physical concepts: 1. Understand the conditions and directions of sliding friction and the factors that affect its magnitude, and master the formula for calculating sliding friction. 2. Understand Conditions for the generation of static friction..

"Friction" interaction PPT courseware:

"Friction" Interaction PPT Courseware Part One: Course Standard Requirements 1. Know the conditions under which sliding friction occurs, and be able to determine its direction and solve for its magnitude..

"Friction" interaction PPT:

"Friction" Interaction PPT Part One Content: Learning Objectives 1. Know the conditions under which sliding friction occurs, and be able to determine its direction and solve for the magnitude of sliding friction. 2. Knowing the conditions under which static friction occurs, you can determine its direction and solve for the magnitude of static friction.

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Update Time: 2024-07-30

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 2 industry PPT template

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