"Friction" Interaction - Force PPT Courseware

Description

"Friction" Interaction——Force PPT courseware

Part One: Learning Objectives

1. Know the definition and classification of friction force. (emphasis)

2. Understand the conditions for the generation of static friction and sliding friction. (emphasis)

3． Able to determine the direction of friction and calculate the magnitude of friction. (difficulty)

4． Understand the concept of maximum static friction and know the relationship between sliding friction and maximum static friction.

Friction PPT, part 2: exploration of new knowledge

Basic combing

1. Sliding Friction

1. Definition: When two ____________ objects slide relative to each other, a ____________________ force will be generated on the contact surface. This force is called sliding friction.

2. Direction: always along ____________ and opposite to the direction of the object ____________.

3． Size: The size of the sliding friction force between two objects is proportional to ______, expressed as F=______, where μ is the proportionality constant (it is the ratio of two forces, without units), called ____________, which The value of is related to the ______ of the two objects in contact with each other, and also related to the condition of the contact surface (such as roughness).

2. Static friction

1. Definition: The friction force produced when there is only ____________ between two objects but no ____________ is called static friction.

2. Direction: always along ____________ and opposite to the direction of the object _______________.

3． Size: When the relative motion trend increases, the static friction force also increases, but there is a limit. The maximum value of this static friction force is called ____________________. The actual static friction force F between two objects is between ______ and _______________, that is, ____________.

self-test

Thinking Analysis

(1) Friction always hinders the movement or movement trend of an object. ()

(2) Friction must occur between two objects in contact with each other. ()

(3) The direction of sliding friction may be the same as the direction of object motion. ()

(4) The magnitude of friction is proportional to positive pressure. ()

(5) The maximum static friction force is slightly larger than the sliding friction force. ()

basic understanding

(1) (2019•Xicheng School Midterm) Which of the following measures are used to reduce friction ()

A. Dripping oil into bearings

B． There are pattern-like grooves on the surface of the tire

C． Squeeze the brakes hard when braking on a bicycle

D． Sprinkle sand and grass on the ground in ice and snow weather

Tip: Choose A. Dropping lubricating oil in the bearing can reduce the friction between the bearing and the wheel, so A is correct; there are pattern-like grooves on the surface of the tires to increase the dynamic friction factor and make the car better in rainy days. Sufficient friction is generated between the bicycle and the ground, so B is wrong; when a bicycle brakes, the brakes are pressed hard to increase the positive pressure between the brakes and the wheels, thereby increasing the friction and making the bike stop easily, so C is wrong; ice and snow Spreading sand and grass on the ground can increase the friction between ice and people (or cars), so D is wrong.

(2) As shown in the figure, if the kitten climbs up and down the tree at a constant speed, the friction forces it experiences are F1 and F2 respectively, then ()

A. F1 goes down, F2 goes up, and F1=F2

B． F1 goes down, F2 goes up, and F1>F2

C． F1 goes up, F2 goes up, and F1=F2

D． F1 is up, F2 is down, and F1=F2

(3) As shown in the figure, the F1 car has very good acceleration performance. Try to analyze the power source of the F1 car during the acceleration phase.

Tip: When the vehicle is not slipping on the ground, the wheels are relatively stationary when in contact with the ground. When the wheels are running at high speed, they move backward relative to the ground, giving the ground a backward static friction force, and at the same time, the ground gives the wheels a forward force. Static friction drives the car to accelerate. This static friction is the power of the car.

Friction PPT, the third part: teacher-student interaction

Understanding and application of static friction

Problem guide

Place the wooden block on a horizontal table and use a spring force gauge to pull the wooden block to the right in the horizontal direction, as shown in the figure.

When the force gauge reads 1 N, the block does not move. When the pulling force is gradually increased to 2 N, the block remains stationary. When the pulling force is further increased to 4 N, the block begins to move. At this time, the pulling force suddenly changes. to 3.8 N. After that, the block moves at a constant speed and the pulling force remains unchanged at 3.8 N.

(1) When the wooden block is subjected to a tensile force of 1 N, it has a tendency to move relative to the table but does not move. What does it mean?

(2) As the external force increases, how does the static friction change?

(3) Where does static friction occur? In what direction?

Key points: (1) Explain that the tabletop exerts a force of 1 N on the wooden block that is opposite to the pulling force and has a magnitude of 1 N. This force is the static friction force of the tabletop on the wooden block.

(2) The magnitude of static friction increases with the increase of external force, but has a maximum value.

(3) Static friction occurs between objects that are relatively stationary but have a tendency to move relative to each other. The direction of static friction is tangent to the contact surface and opposite to the direction of relative motion of the object.

core deepening

【Core Deepening】

1. Conditions for the generation of static friction

(1) The contact surface is rough.

(2) Two objects are relatively stationary but have a tendency to move relative to each other.

(3) There is pressure (elastic force) between the two objects on the contact surface.

The relationship between friction and elasticity: when there is friction between two objects, there must be elasticity; but when there is elasticity between two objects, there is not necessarily friction.

2. Understanding of "Relative Movement Trend"

(1) Relative motion tendency means that an object may move relative to another object in contact with it, but it is still relatively stationary.

(2) The direction of relative movement trend refers to the direction in which objects will move relative to each other if the contact surface is smooth.

3． How to determine the presence or absence of static friction

(1) Conditional judgment method: The contact surfaces are elastic, rough and tend to move relative to each other.

(2) Hypothesis method:

4． How to determine the direction of static friction

Direct method: For situations where the relative motion trend is relatively obvious, it can be directly judged based on "the direction of the static friction force is along the contact surface and is opposite to the direction of the relative motion trend."

Hypothesis method Assume that the contact surface is smooth, determine in which direction the object will slide, thereby determining the direction of the relative movement trend, and then determine the static friction

Directional state method of force When the force on the object is in equilibrium, the direction of the static friction force can be determined based on the balance of the two forces.

Force effect method If there is static friction between objects in contact with each other, there must be a corresponding effect, either to balance other forces or to change the motion state of the object under force. The effect can be used to determine the direction of the static friction force.

Reciprocity of Force Method If there is static friction between two objects A and B, and the direction of the static friction between A and B can be determined, then the direction of the static friction between B and A is opposite to the direction of the static friction between A and B.

5. The magnitude of static friction

The range of static friction is 0

Key competency 1: Understanding of static friction

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

Key ability 2: Judgment of the presence and direction of static friction

Determine whether object A in each picture is subject to friction (A and B are relatively stationary); if so, determine in what direction is the friction force on A?

(1) In picture a, A and B are stationary relative to the ground;

(2) In picture b, A and B are stationary relative to the ground;

(3) In picture c, A and B make uniform linear motion to the right together;

(4) In Figure d, A and B move in a straight line at a uniform speed to the right.

Key capability 3: Calculation of static friction

As shown in the figure, an object with mass M = 2 kg is placed on a rough horizontal surface with a kinetic friction coefficient μ = 0.2. A thin rope of negligible mass is wound around the fixed pulley and connected to a small bucket m0 = 0.1 kg. It is known that the maximum static friction force between M and the horizontal surface Fm=4.5 N, the friction of the pulley is ignored, g=10 N/kg, find the magnitude of the friction force on M in the following situations.

(1) Only hang m0 and when it is in a static state;

(2) When only m0 is hung, but another object M′=3 kg is placed on M;

(3) When only m1 = 0.33 kg of sand is added to the bucket.

Friction force PPT, part 4: practice in class

1. (2019•Qingyang School Level Monthly Examination) Regarding friction, someone summarized "the four are not necessarily certain", among which the wrong statement is ()

A. The direction of friction is not necessarily the same as the direction of motion of the object

B． The direction of static friction is not necessarily collinear with the direction of motion

C． An object subject to static friction or sliding friction is not necessarily at rest or in motion

D． Static friction must be resistance, sliding friction is not necessarily resistance

2. (Multiple choice) Hold an oil bottle with your hand (the bottle is always in the vertical direction), as shown in the picture. Which of the following statements is correct ()

A. The more oil in the bottle, the tighter your hand must hold

B． The tighter you hold your hand, the greater the friction force on the oil bottle.

C． No matter how tightly you hold your hand, the friction force on the oil bottle is always certain.

D． All the above statements are correct

3. As shown in the picture, a car is on a straight road with a wooden box on the car. Try to determine the friction force and direction of the wooden box in the following situations.

(1) When the car accelerates from a standstill (there is no relative sliding between the wooden box and the car surface);

(2) When the car is braking (there is no relative sliding between the two);

(3) When the car is moving at a constant speed (there is no relative sliding between the two);

(4) When the car brakes and the wooden box slides forward on the car;

(5) When the car suddenly accelerates while driving at a constant speed and the wooden box slides on the car.

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For more information about the "Friction Force Interaction Force" PPT courseware, please click the Friction Force PPT Interaction Force PPT tab.

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Update Time: 2024-11-23

This template belongs to Physics courseware People's Education Press High School Physics Compulsory Course 1 industry PPT template

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