"Application of Equilibrium Conditions" Force and Balance PPT

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"Application of Equilibrium Conditions" Force and Balance PPT

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

Scientific thinking: 1. Consolidate common methods of handling static equilibrium through examples. 2. Master how to analyze dynamic equilibrium problems through analytical and graphical methods. 3. Master methods to solve critical problems and extreme value problems.

Application of Balanced Conditions PPT, Part 2: Collaborative exploration to overcome difficult problems

static equilibrium

1. static equilibrium definition

Static equilibrium refers to the equilibrium when an object remains at rest under the action of a common point force.

2. Understanding static equilibrium

(1) Kinematic characteristics: The speed of an object in static equilibrium is zero.

(2) Equilibrium condition: The resultant force on an object in static equilibrium is zero.

(3) Example: In daily life, triangular brackets are widely used for their superior balance and stability. For example, static balancing devices such as steel frame structures on the roofs of large exhibition halls and gymnasiums, street light brackets on the roadside, and tower crane brackets on construction sites mostly adopt triangular structures.

[Example 1] Hang a football at point A with a net bag along a smooth wall. As shown in the figure, the mass of the football is m. The mass of the net bag is not included. The contact point between the football and the wall is B. The angle between the suspension rope and the wall is For α, find the pulling force of the hanging rope on the ball and the supporting force of the wall on the ball.

Thoughts: ① The ball is at rest, and the net external force it experiences is zero.

②Selecting the ball as the research object can be solved by the synthesis method, decomposition method, and orthogonal decomposition method.

regular method

Methods and steps to solve static balance problems

(1) To deal with balance problems, commonly used methods include synthesis method, decomposition method, similar triangle method, orthogonal decomposition method, etc.

(2) Steps to solve problems using equilibrium conditions

①Clear the research object (object, particle or knot of rope, etc.);

② Carry out force analysis on the research object;

③Establish an appropriate coordinate system, apply the equilibrium conditions of common point forces, and choose an appropriate method to list the equilibrium equation;

④Solve the equation and discuss the results.

dynamic equilibrium

1. Definition of dynamic balance

Dynamic balance means that an object maintains a state of uniform linear motion under the action of a common point force, or that the object's motion state slowly changes by controlling certain physical quantities. During this process, the object is always in a series of equilibrium states.

2. equilibrium conditions

The resultant force of the common point forces on the object is zero.

3. Problem-solving ideas

Turn "movement" into "quietness" and find "movement" from "quietness".

[Example 2] As shown in the figure, the ball is sandwiched between the vertical wall AC and the wooden board BC. Disregarding friction, the pressure of the ball on the wall is N1 and the pressure of the ball on the wooden board is N2. Gradually lower the wooden board BC to the horizontal In the process, which of the following statements is correct ()

A. Both N1 and N2 increase

B． Both N1 and N2 decrease

C. N1 increases and N2 decreases

D． N1 decreases and N2 increases

Idea inspiration: Select the ball as the research object ⇨ Conduct force analysis on the ball and make a force vector triangle ⇨ Judge the change in force based on the change in the length of the directed line segment

regular method

Dynamic balance and its analysis methods

(1) The dynamic balance of an object refers to the balance of an object in motion. By controlling a certain physical quantity, the state of the object changes slowly. During this process, the object is always in a series of dynamic equilibrium states.

(2) Two analysis methods for dynamic balance problems

① Analytical method: Conduct force analysis on any state of the research object, establish a balance equation, find the general functional formula of the dependent variable and the independent variable, and then determine the change of the dependent variable based on the change of the independent variable.

② Graphical method: Conduct force analysis on the research object, and then draw vector diagrams of the forces in different states (drawn in the same diagram) according to the parallelogram rule or the triangle rule, and then draw vector diagrams of the forces in different states according to the directed line segments (representing the force) The change in length can be used to determine the change in each force.

Critical and extreme value problems in equilibrium problems

1. Critical issues

Critical state refers to the transition state in the process of a certain physical phenomenon (or physical state) changing into another physical phenomenon (or physical state). It can be understood as "happening to appear" a certain physical phenomenon, or it can be understood as "happening not to appear" a certain physical phenomenon. Problems involving critical states are called critical problems.

2. extreme value problem

Extreme value refers to the maximum or minimum value that appears during the change process of the physical quantity describing the object. Problems involving extreme values ​​are called extreme value problems.

3. Methods for solving critical and extreme value problems

One is the physical analysis method, which solves the problem by grasping the critical (or extreme value) conditions through the analysis of the physical process. For example, the critical condition for the separation of two objects is that the elastic force between the two objects is zero. The other is the mathematical method. By analyzing the problem, writing the functional relationship between physical quantities (or making a function image) according to the laws of physics, using mathematical knowledge (such as finding the extreme value of a quadratic function, discussing the extreme value of a formula, trigonometric function extreme value, etc.) to solve.

Application of balanced conditions PPT, the third part: reaching the standard in court and solidifying the double base

1. A small weight G is tied under a hydrogen balloon. The weight only moves in a straight line at a constant speed under the action of gravity and the tension of the rope, regardless of the influence of air resistance and wind. The direction of the movement of the weight is as shown by the arrows in each figure, then the following In the figure, the possible positions of the balloon and weight G in motion are ()

A. The weight G is acted upon by gravity and the pulling force of the rope. From the balance of forces, it can be seen that the two forces must be in opposite directions, so the suspension line is vertical. ]

2. As shown in the figure, an ant with mass m crawls in a hemispherical bowl with radius R and stops at point P at a height R2 from the bottom of the bowl. If the acceleration of gravity is g, then the friction force it experiences at point P The size is ()

A.12mg B.22mg

C.32mg D． mg

3. As shown in the picture, use two light ropes OA and OB to hang the flowerpot between two vertical walls. The OB rope is horizontal at the beginning. Now keep the position of point O unchanged, change the length of rope OB so that the right end of the rope slowly moves up from point B to point B′. At this time, the angle θ between OB′ and OA is <90°. Assume that during this process, the The pulling forces are FOA and FOB respectively, then the following statement is correct ()

A. FOA keeps decreasing B. FOA keeps increasing

C. FOB keeps decreasing D. FOB keeps increasing

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Update Time: 2024-09-20

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

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