"Balance of Common Point Forces" Force and Balance PPT Download

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"Balance of Common Point Forces" Force and Balance PPT Download

Part One: Curriculum Standard Requirements

1. Know what equilibrium is and the two forms of equilibrium.

2. Master the conditions for common point force balance and the concept of force balance.

3. Will use the equilibrium conditions of common point forces to answer practical problems.

Balance of Common Point Force PPT, Part 2: New Self-study Textbook

1. The equilibrium state of an object

1. Fill it out

Equilibrium state: The state in which an object ___ or performs ___ motion.

2. Give a verdict

(1) When the speed of an object is equal to zero at a certain moment, it must be in equilibrium. ( )

(2) When an object remains stationary relative to another object, it must be in a state of equilibrium. ( )

(3) In a 100-meter race, at the moment of starting, the athlete's speed is zero and he is in a state of equilibrium. ( )

(4) The gymnast is in a balanced state when doing flipping movements on the balance beam. ( )

3. think about it

Balance is everywhere in life. Towering peaks in nature, cars traveling at a constant speed, and even the famous Leaning Tower of Pisa are all in a state of balance. Think carefully about the differences between them. What exactly does the word "equilibrium" mean in physics?

2. Balance conditions for common point forces

1. Fill it out

(1) The equilibrium condition of an object: The equilibrium condition of an object under the action of a common point force is that the resultant force is ___, that is, Fsum = 0.

(2) Balance of forces: If the resultant force of several common-point forces acting on an object is zero, this situation is called balance of forces.

2. Give a verdict

(1) An object whose combined external force remains constant is in equilibrium. ( )

(2) When the net external force on an object is zero, it must be in equilibrium. ( )

(3) Two forces of equal magnitude, opposite directions, and acting on the same straight line must be balanced forces. ( )

(4) If an object is in equilibrium, the net external force it experiences must be zero. ( )

3. Choose one

(1) [ Multiple choice

A. 5 N, 7 N, 8 N　B. 2N, 3N, 6N

C. 1 N, 5 N, 10 N D.1 N, 10 N, 10 N

(2)[Multiple Choice]As shown in the figure, an object with mass m is acted upon by a thrust F and moves in a straight line at a uniform speed in the horizontal direction. It is known that the angle between the thrust F and the horizontal plane is θ, and the kinetic friction factor between the object and the ground is μ, then the friction force experienced by the object is ()

A. Fsin θ B. Fcos θ

C. μF D.μ(mg＋Fsin θ)

The balance of common forces PPT, the third part: improving new knowledge

Breakthrough point 1: Understanding of equilibrium state and equilibrium conditions

[Learn thoroughly and apply it]

1. Understanding equilibrium states from a kinematic perspective

(1) The equilibrium state refers to an object at rest or in a state of uniform linear motion. At this time, the object's acceleration is zero. In turn, an object with zero acceleration must be in a state of equilibrium.

(2) Understanding of stillness: Stillness and speed v=0 are not the same thing. The object remains stationary, indicating that v=0 and a=0, both of which are true at the same time. If only v=0, a≠0, like the object thrown to the highest point, the object cannot remain stationary at this time, and it is not in a state of equilibrium.

2. Understanding equilibrium states from a dynamic perspective

The net external force on an object in equilibrium is zero, and conversely, the net external force on an object is zero, so it must be in equilibrium.

3. Four common corollaries of equilibrium conditions

(1) Two force balance condition: the two common point forces are equal in magnitude and opposite in direction.

(2) Three force balance conditions: When three common-point forces are balanced, the resultant force of any two of them must be equal in magnitude and opposite in direction to the third force, and on the same straight line.

(3) When an object is in equilibrium under the simultaneous action of n common point forces, the resultant force of these forces in any direction is zero. The resultant force of any (n-1) force must be equivalent and opposite to the nth force, acting on the same straight line.

(4) When an object is in equilibrium under the action of multiple common-point forces, the forces connected end to end must form a closed polygon.

[Typical Example 1] [Multiple Choices]Which of the following statements about the balance and equilibrium conditions of common point forces is correct ()

A. Two relatively stationary objects are in equilibrium

B． An object is in equilibrium when it is in free fall

C. If an object is in equilibrium, the net force on the object in any direction must be zero

D． If an object is in equilibrium under the action of three common-point forces, then the resultant force of any two forces is equal in magnitude and opposite in direction to the third force.

[Practice clearly]

1. Regarding the equilibrium state, which of the following statements is correct ()

A. An object in free fall is in equilibrium at its highest point

B． The wooden block is placed on the inclined surface of the inclined plane and moves to the right with the inclined plane at a constant speed. The wooden block is in a state of equilibrium.

C. The wooden block is placed on the inclined surface of the inclined plane and accelerates uniformly to the right together with the inclined plane. The wooden block is in a state of equilibrium.

D． A cup resting on a horizontal table in a uniformly accelerating train is in equilibrium.

2. As shown in the figure, a box of apples is stationary on an incline with an inclination angle of θ. There is an apple with mass m in the center of the box. It is subject to the direction of the force exerted on it by the surrounding apples ()

A. Upward along the slope B. down the slope

C. Vertically upward D. Vertically inclined upward

3. As shown in the figure, an object is at rest under the action of four forces F1, F2, F3, and F4. If the direction of F4 rotates 60° counterclockwise without changing its size, the other three forces The magnitude and direction remain unchanged, then the resultant force on the object at this time is ()

A. F4 B. 2F4

C. 2F4 D. Unable to determine

Breakthrough point 2: Application of common point force balance conditions

[Learn thoroughly and apply it]

1. Two expressions of equilibrium conditions

(1) F combined = 0.

(2) Orthogonal representation F plus x = 0, F plus y = 0, where F plus x and F plus y are the resultant forces on the x-axis and y-axis that the object experiences after orthogonal decomposition of the forces respectively.

2. Three commonly used problem-solving methods for common-point force balance problems

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, acting on the same straight line.

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: When an object is acted upon 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.

[Typical Example 2] Use a net bag to hang a football at point A on a smooth wall. The contact point between the football and the wall is B (as shown in the figure). The mass of the football is m. The clamp between the suspension rope and the wall is The angle is α, and the mass of the net bag is ignored. Find the pulling force of the hanging rope on the ball and the supporting force of the wall on the ball.

[Inspiration]

(1) The football is at rest and the net external force it receives is zero.

(2) Selecting football as the research object can be solved by using the synthesis method, decomposition method, and orthogonal decomposition method.

[Regular method]

Steps to solve problems using equilibrium conditions

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

(2) Analyze the motion state of the research object and determine whether the object is in equilibrium.

(3) Conduct stress analysis on the research object and draw a stress diagram.

(4) Establish an appropriate coordinate system, apply the equilibrium conditions of common point forces, and choose an appropriate method to formulate the equilibrium equation.

(5) Solve the equation and discuss the results.

The balance of common forces PPT, the fourth part: training new literacy

1. Classification of coplanar forces (physical concepts of core competencies)

Figures A, B, C, and D respectively draw a situation where a wooden rod with gravity G is in equilibrium under the joint action of forces F1 and F2. These forces are all located in the same plane. According to the geometric relationship of the action lines of each force in each picture, the forces in the above four situations can be divided into two categories. Which situations do you think belong to the same category? On what basis do you divide it?

[ Tips Forces that do not intersect at one point are non-copoint forces.

2. Discover good classic questions and practice the classic questions so that one can be as good as ten

A kindergarten wants to build a slide in an open space (as shown in Figure A). According to the size of the open space, the horizontal span of the slide is determined to be 6 m. During design, the kinetic friction factor between the skateboard and the children's pants material is 0.4. In order for children to slide down the skateboard when playing on the slide, how high must the slide be?

[Analysis] Abstract the slide as an inclined plane model (as shown in Figure B), and take the child who is sliding down at a constant speed as the research object.

The child is acted upon by three forces: gravity G, the support force FN of the inclined plane, and the sliding friction force Ff.

When the resultant force of these three forces is 0, the child can gain a certain speed on the skateboard and then slide down at a constant speed, then the height of the slope is the required height of the slide.

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

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Update Time: 2024-09-01

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

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