"Friction" Interaction PPT Download

Description

"Friction" Interaction PPT Download

The first part of the content: [Learning literacy·clear goals]

Physical concepts: 1. Understand the conditions and direction of sliding friction and the factors that affect its magnitude, and master the formula for calculating sliding friction. 2. Understand the conditions and direction of static friction, and understand the concept of maximum static friction. 3. Understand The application of friction control in real life.

Scientific thinking: 1. Be able to comprehensively judge the direction of friction. 2. Be able to calculate the magnitude of friction.

Friction PPT, part 2: independent preview to explore new knowledge

Knowledge sorting

1. Sliding friction

1. Definition: When two objects contact and _______ each other and slide relative to each other, the force generated on the contact surface that hinders _______.

2. The direction and effect of sliding friction: The direction of sliding friction is always _______ with the contact surface and opposite to the _______ direction of the object. Therefore, the effect of sliding friction always hinders _______ between objects.

3. The magnitude of sliding friction

(1) The magnitude of sliding friction: is directly proportional to _______, and is also related to the properties of the contact surface.

(2)Formula: f=_______.

Among them, N represents _______, and μ is the kinetic friction factor, which is related to _______ and ______________ of the contact surface.

2. Static friction

1. Definition: When two objects that are in contact or squeezing each other do not move relative to each other, but have a tendency to move relative to each other, a force that hinders _______ will be generated on the contact surface. This force is called static friction.

2. Conditions for production: The object directly _______, the contact surface _______, there is _______ between the contact surfaces, and there is _______.

3. Direction: Always tangent to _______ and opposite to the direction of _______.

4. Effect: Hindering the tendency of relative sliding between objects.

5. Size: determined by _______ and changes with changes in external forces.

6． maximum static friction

(1) Definition: The _______ of the static friction force between an object and the contact surface, that is, the static friction force when the object begins to slide along the contact surface under the action of an external force, is represented by fmax.

(2)Related factors

① Proportional to the pressure between the two objects.

②Related to the nature of the contact surface.

3. Control of friction

Friction control

Ways to increase

1Increase the _______ between objects.

2Increase the _______ of the contact surface.

Ways to reduce

1 Reduce the _______ between objects.

2 Reduce the _______ of the contact surface.

3 Use friction.

Basic self-test

1. Think and judge (mark “√” if correct, “×” if incorrect)

(1) When an object slides on the surface of another object, friction must occur. ( )

(2) The direction of sliding friction is along the contact surface and opposite to the direction of movement of the object. ( )

(3) A stationary object may be subject to sliding friction. ( )

(4) Static friction always occurs between objects that are relatively stationary and have a tendency to move relative to each other. ( )

(5) A moving object cannot be affected by static friction. ( )

(6) The static friction force on a wooden box resting on a horizontal rough ground is related to the thrust force. ( )

2. Which of the following statements about friction is correct ()

A. There must be friction between two objects in relative motion

B． Friction always hinders the movement of an object

C. The direction of friction on a moving object is always opposite to the direction of motion

D． There may also be frictional interaction between two relatively stationary objects.

Friction PPT, Part 3: Collaborative exploration to overcome difficult problems

Understanding friction

Comparison of Static Friction and Sliding Friction

Generate conditions

static friction

① There is elastic force between the two objects ② The contact surface is rough ③ There is a tendency of relative movement

sliding friction

① There is elastic force between the two objects ② The contact surface is rough ③ There is relative motion

For training

1. Which of the following statements about sliding friction is correct ()

A. The direction of sliding friction is always opposite to the direction of motion of the object

B． Sliding friction always hinders the movement of an object

C. The direction of sliding friction is always opposite to the direction of relative motion of the object

D． When two objects in contact with each other slide relative to each other, they are both affected by sliding friction.

2. Regarding static friction, which of the following statements is correct ()

A. Two objects with rough surfaces will produce static friction as long as they are in direct contact.

B． Static friction always hinders the motion of an object

C. The direction of static friction is opposite to the direction of relative motion between objects.

D． The static friction force between two objects is always a constant value

[Misunderstanding Warning]

Three major misunderstandings about friction

(1) It is mistakenly believed that a stationary object can only be affected by static friction, and a moving object can only be affected by sliding friction. In fact, no matter whether the object is stationary or moving, it may be affected by static friction or sliding friction.

(2) It is mistakenly believed that the effect of friction always hinders the movement of objects. In fact, friction can be used as both power and resistance.

(3) It is mistakenly believed that the direction of friction force is always opposite to the direction of movement of the object. In fact, the direction of friction force can be opposite to the direction of movement of the object, or it can also be the same as the direction of movement of the object.

Determining the presence and direction of static friction

1. Determine the presence or absence of static friction based on the motion state of the object

A and B are stacked together, and object B is pulled with force F, while A and B are both stationary, as shown in Figure A. Assume that object B has friction on A, then A only experiences one force in the horizontal direction and cannot remain stationary, so there is no static friction between A and B.

2. Determine the direction of static friction based on the interaction of forces

A and B are stacked together, and object A is pulled with force F, while A and B are both stationary, as shown in Figure B. Assuming there is no static friction between A and B, A is only acted upon by one force F in the horizontal direction and cannot remain stationary, so there must be static friction between A and B. According to the principle of two-force balance, the static friction force of B on A must be to the left. According to the principle of force interaction, the static friction force of A on B must be to the right, so the static friction force of the ground on B must be to the left.

3. Use the hypothesis method to determine the direction of relative movement trends

(1)Method

Assume that the research object and the contacted object are smooth. If relative sliding occurs between them, the relative sliding direction is the direction of the original relative movement trend; if relative sliding does not occur between them, it means that the two contacting objects are not Relative sliding trend.

(2) Steps

①Determine the object to be studied.

②Select the object in contact with the object under study as the reference system.

③ Assuming that the contact surface is smooth, analyze the relative motion trend direction of the research object and the reference system.

④The direction of static friction is opposite to the direction of relative motion trend.

prescribed method

1 The key to using the hypothesis method to determine whether friction exists is to assume that the contact surface is smooth, and then analyze the movement of the research object.

2. For relatively complex questions, we generally first analyze objects with simple forces, and then analyze the forces on objects in contact with them based on the reciprocity of forces.

Calculation of friction force

1. Calculation of sliding friction force

(1) Formula method: Calculated according to f=μN.

(2) Two-force balance method: When the object is in equilibrium (uniform linear motion or stationary), the solution is based on the conditions of two-force balance.

2. Calculation of static friction force

(1) According to the force situation and the balance condition of the two forces, the magnitude of the static friction force is always equal to the external force that causes the object to move relative to the object.

(2) As the relative motion trend increases, the static friction force gradually increases, but it cannot increase all the time. When the static friction increases to a certain value, the object will begin to slide along the contact surface, and the static friction is replaced by sliding friction. The maximum value that static friction can reach is called the maximum static friction force fmax. The range of static friction force is 0

(3) The maximum static friction force fmax is slightly larger than the sliding friction force. In general, for the convenience of analyzing the problem, the two can be considered equal, that is, fmax=μN.

Friction force PPT, the fourth part: reaching the standard and solidifying the double base in the hall

1. Regarding the kinetic friction factor, which of the following statements is correct ()

A. The greater the pressure between the two contact surfaces, the greater the kinetic friction factor

B． The greater the sliding friction between two objects, the greater the kinetic friction factor

C. The coefficient of kinetic friction between two objects is directly proportional to the sliding friction force and inversely proportional to the pressure between the two objects

D． The kinetic friction factor between two objects is determined by the materials of the two objects and the roughness of the contact surface, and has nothing to do with sliding friction and normal pressure.

2. (Multiple choice) As shown in the figure, there is an inclined conveyor belt transmission device. Regarding the friction force on objects on the conveyor belt, which of the following statements is correct ()

A. If the conveyor belt is stationary and the object is stationary, the object will experience static friction upward along the conveyor belt.

B． If the conveyor belt is stationary and the object is stationary, the object will experience static friction downward along the conveyor belt.

C. If the conveyor belt rotates clockwise at a constant speed and the object moves upward with the conveyor belt at a constant speed, the object will experience static friction upward along the conveyor belt.

D． If the conveyor belt rotates clockwise at a constant speed and the object moves upward with the conveyor belt at a constant speed, the object will experience sliding friction upward along the conveyor belt.

3. (Multiple choice) As shown in the picture, there are three identical objects stacked together and placed on a rough horizontal ground. The objects are not smooth. Now a horizontal force F acts on object B, and the objects remain stationary. Which of the following statements is correct ()

A. The friction force exerted by C on the ground is F, and its direction is horizontally to the left.

B． A is acted upon by horizontal friction force to the right

C. The friction force between B and C is F and the direction is horizontal to the right.

D． The magnitude of the friction force between C and B is F, and its direction is horizontally to the right.

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Update Time: 2024-11-22

This template belongs to Physics courseware Lu Ke Edition High School Physics Compulsory Course One industry PPT template

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