"Balance of Common Point Forces" Interaction - Force PPT courseware

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"Balance of Common Point Forces" Interaction - Force PPT courseware

Part One: Learning Objectives

1. Understand the motion characteristics of equilibrium state, and master the relationship between motion state and force.

2. Understand the conditions for common point force balance and apply the conditions to solve practical problems.

3. Master the characteristics of dynamic balance and skillfully solve its problems.

4. Master the application of holistic method and isolation method.

Balance of common point force PPT, part 2: exploration of new knowledge

Basic combing

1. understanding of equilibrium

(1) Two equilibrium states: The equilibrium state under the action of a common point force includes a stationary state and a state of uniform linear motion.

(2) The difference and connection between "still" and "v=0"

When v=0a=0, it is stationary, and it is an equilibrium state. When a≠0, it is not an equilibrium state.

In short, the equilibrium state refers to the state where a=0.

2. Conditions for common point force balance

expression:_________.

self-test

basic understanding

(1) The illustration is a commonly used artistic form by the humorist Chaplin. He leans sideways and relies on the support of a cane to balance his body. Which of the following statements is correct ()

A． Level ground has no frictional effect on the cane

B． There is no friction when facing Chaplin on a horizontal surface

C. The elastic force of the horizontal ground on the stick is directed upward along the stick

D. The direction of force acting on Chaplin when facing it horizontally must not be vertically upward.

Tip: Choose D. The cane has a tendency to slide to the right, and Chaplin has a tendency to slide to the left. The horizontal surface has a frictional effect on both the cane and Chaplin. Options A and B are wrong; the horizontal surface has a friction effect on the cane. The direction of the elastic force is perpendicular to the ground and upward, option C is wrong; the friction force direction of the ground facing Chaplin is to the right, so the direction of the horizontal force facing Chaplin is obliquely to the upper right, and must not be vertically upward, option C D is correct.

(2) As shown in the figure, a small ball is placed between the wooden board and the vertical wall. Let the elastic force of the wall facing the ball be FN1, and the elastic force of the wooden board facing the ball be FN2. Taking the horizontal straight line formed by the connection point of the wooden board and the wall as the axis, slowly turn the wooden board from the position shown in the figure to the horizontal position. Disregarding friction, in this process ()

A． FN1 always decreases and FN2 always increases

B． FN1 always decreases, FN2 always decreases

C. FN1 first increases and then decreases, FN2 always decreases

D. FN1 first increases and then decreases, FN2 first decreases and then increases.

The balance of common forces PPT, the third part: teacher-student interaction

Understanding of common point force balance conditions

Problem guide

We live in a colorful world where objects come in all shapes and sizes. The ancient boulders have been standing miraculously for thousands of years (pictured). People in the city have their own ways to find stillness while moving. When you go to a large shopping mall, as long as you stand still, the escalator will take you up and down the stairs steadily and at a steady speed (as shown in the picture). From a physical point of view, if an object remains stationary or moves in a straight line at a uniform speed, we say that the object is in equilibrium. Therefore, people standing on boulders and uniform-speed elevators are in a state of balance. So, what are the conditions required to keep an object balanced?

Key points: If an object is balanced by two forces, the two forces must be equal and opposite and act on a straight line, that is, the net force is zero. If an object is balanced by multiple forces, according to the force synthesis rule, we can equivalently replace any two common point forces with a resultant force. According to this, more than three common point forces can ultimately be equivalently simplified to Two common point forces. It can be seen that the balance of three or more common-point forces can ultimately be simplified to the balance of two forces. According to the two-force balance condition, we can conclude that the equilibrium condition of an object under the action of a common point force is that the resultant force is zero, that is, Fsum = 0.

【Core Deepening】

The object is acted upon by a common point force. Which of the following statements is correct ()

A． If the object's speed is equal to zero, the object must be in equilibrium

B． When an object remains at rest relative to another object, the object must be in equilibrium

C. When the net force on an object is zero, it must be in equilibrium

D. When an object moves with uniform acceleration, the object is in equilibrium

[ Analysis An object with a speed of zero does not necessarily have zero force, so it is not necessarily in a state of equilibrium. Choice A is wrong; when an object is at rest relative to another object, the object is not necessarily at rest relative to the ground, such as when another object is moving at a variable speed. , the object also performs variable-speed motion, and the object is in a non-equilibrium state, so option B is incorrect; option C meets the equilibrium conditions and is the correct option; the object moves with uniform acceleration and the resultant force is not zero, so it is not in equilibrium, option D wrong.

(Multiple choice) Regarding common point force, which of the following statements is correct ()

A． If two forces acting on an object are equal in magnitude and opposite in direction, then the two forces are copoint forces.

B． If two forces acting on an object are a pair of balanced forces, then the two forces are copoint forces.

C. Several forces acting on an object may also be co-point forces if their points of action are not at the same point.

D. Several forces acting on an object are copoint forces if their lines of action can intersect at one point.

Analysis: Choose BCD. If several forces acting on an object act on the same point of the object or do not act on the same point of the object, but the lines of action of the forces intersect at one point, then these forces are co-point forces. , so options C and D are correct; forces of equal magnitude and opposite directions may not necessarily act at the same point, but a pair of balancing forces must act on the same straight line of the same object, which is a co-point force, so option A is incorrect and option B is correct. ．

Common methods to solve balance problems

Problem guide

As shown in the figure, the gravity of the heavy object is G. The light rope AO is fixed to the A and B ends of BO. When balanced, AO is horizontal. The angle between BO and the vertical direction is θ. Can we use the decomposition method and Comprehensive method to determine the magnitude of AO's pulling force FT1 and BO's pulling force FT2 using two methods?

Key points: Select point O as the research object. Its force is shown in Figure A. Point O is acted upon by three forces: the pulling force of the weight on O is G, the pulling force of the AO rope FT1, and the pulling force of the BO rope FT2. For example As shown in Figure B, the resultant force of FT1 and FT2 is equal to the gravity, and the pulling force of the two ropes is solved in the triangle. As shown in Figure C, decompose the gravity along the direction of the two ropes, and solve the tension of the two ropes in the triangle.

【Core Deepening】

1. Common methods for dealing with static equilibrium problems

Method content

Synthesis method If an object is balanced by three common point forces, then the resultant force of any two forces must be equal in magnitude and opposite in direction to the third force.

Decomposition method: An object is balanced by three common-point forces. If a certain force is decomposed according to the effect of the force, then its component force and the other two forces meet the equilibrium conditions.

Orthogonal decomposition method: An object is balanced by three or more forces. The forces on the object are decomposed into two groups that are perpendicular to each other. Each group of forces satisfies the equilibrium condition.

Triangular method of force: For an object that is balanced by three forces, translate the vector diagram of the force so that the three forces form a vector triangle connected end to end, and solve the unknown force based on mathematical knowledge such as the sine theorem, the cosine theorem or similar triangles.

2. General ideas for solving the problem of object balance under the action of common point forces

Balance of Common Point Force PPT, Part 4 Content: Ability Drills in the Classroom

1. (2019 Jining School Level Monthly Examination) As shown in the figure, a person stands on the horizontal pedal of an escalator and moves diagonally upward with the escalator at a constant speed, regardless of air resistance. The following statement is correct ()

A． People are affected by gravity and supporting forces

B． People are affected by gravity, support and friction

C. Human gravity and human pressure on the pedal are a pair of balancing forces

D. The pressure a person exerts on the pedal is the person's gravity

Analysis: Choose A. A person stands on the escalator. The person is subject to the vertical downward gravity and the vertical upward support force. The person is stationary relative to the escalator, has no movement and no tendency to move, and the person is not subject to friction. function, so A is correct and B is wrong; gravity and supporting force are a pair of balancing forces, and human gravity and human pressure on the pedal are not balancing forces. C is wrong; human pressure on the pedal is an elastic force, and human gravity is the force of gravity. 2. The two are forces with different properties, so D is wrong.

2. (Multiple choices) (2019•Hubei Eight Schools Joint Entrance Examination) As shown in the figure, two balls A and B have masses m, fixed at both ends of a light spring, and suspended at point O with thin ropes respectively. Ball A is at At the junction of a smooth vertical wall and a smooth horizontal wall, it is known that both balls are in equilibrium, and OAB exactly forms an equilateral triangle, then the following statement is correct (the acceleration of gravity is g) ()

A． Ball A may be acted upon by four forces

B． The elastic force of the spring on ball A is greater than the elastic force on ball B.

C. The pulling force of rope OB on ball B must be equal to mg

D. The pulling force of rope OA on ball A is equal to or less than 1.5mg

Analysis: Choose ACD. Analyze the force on ball B. According to the common point force balance, it can be seen that the force exerted by the spring and the rope on ball B is mg. Option C is correct; for the same spring, the elastic force generated is equal everywhere, so the spring The elastic force on ball A is equal to the elastic force on ball B. Option B is incorrect. Analysis of ball A shows that it must be affected by gravity, the elastic force of the spring, and the supporting force of the wall. It may be affected by the supporting force of the ground and the pulling force of the rope. The ground's One of the supporting force and the pulling force of the rope may also be 0. When the supporting force of the ground surface on ball A is 0, the pulling force on the rope is the largest, which is equal to the sum of the gravity and the vertical component of the spring, which is 1.5mg, so the option A and D are correct.

Keywords: PPT courseware for high school physics compulsory course 1 from the People's Education Press is available for free download, balance of common point forces PPT download, interaction force PPT download, .PPT format;

For more information about the "Equilibrium Interaction Forces of Common Point Forces" PPT courseware, please click the "Equilibrium Interaction Forces of Common Point Forces ppt" tag.

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Update Time: 2024-09-09

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

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