"Gong" Work and mechanical energy PPT

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"Gong" Work and mechanical energy PPT

Part One: Preview Perception

1. Work in mechanics

1. Definition of work: If a force acts on an object and the object moves a certain distance in the direction of the force, it is said that the force has done work on the object.

2. Two necessary factors for doing work

(1) Force acting on an object.

(2) The distance the object moves in the direction of this force.

2. Calculation of work

1. Content: Work is equal to the product of force and the distance the object moves in the direction of the force.

2. Formula: W=Fs.

3. Units, symbols and conversions of various physical quantities

Gong PPT, Part 2: Interactive Classroom Understanding

Determining whether an object does work

1. To do work, two necessary conditions must be met

(1) A force must act on the object.

(2) The force-bearing object must pass a certain distance in the direction of the force.

2. Three situations in which force does not do work on the object

(1) Lack of force and reactive power: The object passes a certain distance by inertia. In this case, there is distance forcelessness.

(2) Distance-deficient reactive power: A force acts on the object, but the object has no moving distance.

(3) Vertical reactive power: A force acts on the object, and the object moves a certain distance, but the direction of the force is perpendicular to the direction of movement of the object.

[Example] In the process shown in the figure, the work done by the person on the object is ()

When considering the problem of work, you can follow the following three steps: (1) Whether the object is acted upon by a force, there is no problem of doing work for an object without force; (2) Whether the object is moving, there is no problem of doing work for an object that is not moving; (3) Determine the relationship between the direction of the force on the object and the direction of motion. If the two directions are perpendicular, no work will be done; if the two directions are not perpendicular, then work will be done.

Analysis To correctly understand the two necessary factors for doing work, one is to see whether a force acts on the object, and the other is to see whether the object has passed a distance in the direction of the force. Both are indispensable. In option B, the athlete exerts an upward force on the barbell and moves a distance in the direction of the force, so work is done on the barbell.

Answer B

Functional PPT, the third part: try the application

1. Two necessary factors for doing work

1. Among the following statements about work, which one is correct ()

A. As long as a force acts on an object, work must be done

B. As long as the object moves a distance, work must be done

C. As long as a force acts on an object and the object moves a distance, work must be done.

D. As long as a force acts on an object and the object moves a distance in the direction of the force, work must be done.

2. During a weightlifting competition, athletes quickly lift the barbell over their heads in the first stage, and keep the barbell in the air for 3 seconds in the second stage. Which of the following statements about the work done by athletes on the barbell is correct ()

A. He did no work in the first stage

B. He did no work in the second stage

C. He did no work in either stage

D. He did work in both stages

2. Calculation of work

3. As shown in the figure, an object with a gravity of 100 N is pulled by a horizontal force and moves 5 m to the right on a horizontal ground at a constant speed. The friction force on the ground on the object is 20 N, then ()

A. The work done by gravity is 500 J

B. The magnitude of the pulling force is 100 N

C. The magnitude of the pulling force is 120 N

D. The work done by the pulling force is 100 J

4. The work done by gravity on an egg thrown by an actor in an acrobatic performance from the highest point to the lowest point is approximately ()

A.0.2 JB.2 J

C.20 J D.200 J

Keywords: Free download of PPT courseware for the second volume of eighth-grade physics published by the People's Education Press, download of work PPT, download of work and mechanical energy PPT, .PPT format;

For more information about the PPT courseware "Work and Mechanical Energy", please click on the Work and Mechanical Energy ppt Work ppt tab.

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Update Time: 2024-07-28

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 2 industry PPT template

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