"Exploring - Does Using Machinery Save Work?" Machinery and Work PPT Courseware

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"Exploring - Does Using Machinery Save Work?" Machinery and Work PPT Courseware

Knowledge review

1. Can labor-saving machines or labor-intensive machines save work?

2. Can a machine with large self-weight and friction or a machine with negligibly small self-weight and friction save power?

Mechanical efficiency

1. Useful work and extra work

1. Useful work: "W is useful"

The valuable work done by machinery to the outside world

Our purpose is to use machinery to lift heavy objects, so the work done by machinery on heavy objects is valuable, and we call it useful work.

2. Extra work: "W extra"

The useless work done by a machine to overcome its own gravity and friction

When we use machinery to lift heavy objects, we need to overcome friction to do work, and we also need to overcome the gravity of the machine itself to do work. This part of the work is not what we want, but it is work that we have to do. This kind of work is called extra work.

3. Total work: “W total” The work done by the power on the machine

The relationship between the three: W total = W useful + W extra

2. Mechanical efficiency

Mechanical efficiency: "ŋ"

(1) Concept: The ratio of useful work to total work is called mechanical efficiency

(2) Expression: ŋ = W useful/W total × 100 %

(3) Because W useful < W total

Therefore, ŋ < 1

The mechanical efficiency of the crane is 40%~50%

The mechanical efficiency of the pulley block is 60%~80%

Exchange and discussion

1. Discuss how to improve the mechanical efficiency of the pulley block and give it a try.

2. Figure 9-36 shows a scene where residents used pulleys to lift water after the water supply system in a certain area failed. In this scenario, which part of the work done by a person is useful work and which part is extra work?

Assume that the inclined surface is smooth and frictionless.

According to the principle of work: W useful = W useless

Gh=F·L F/G=h/F

The length of the incline is several times the height of the incline, and the thrust is a fraction of the weight of the object.

To raise objects to the same height, the longer the slope, the easier it is to lift it.

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For more information about the PPT courseware "Machines and Power to Explore whether Using Machinery Saves Work", please click on the "Machine and Power ppt to Explore whether Using Machinery Saves Work" ppt tag.

"Exploring - Whether Using Machinery Saves Work" Machinery and Work PPT Courseware 4:

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"Exploring - Whether Using Machinery Saves Work" Machinery and Work PPT Courseware 3:

"Exploring whether using machinery saves work" Machinery and Work PPT Courseware 3 Teaching objectives: (1) Knowledge objectives 1. Know that using machinery does not save work. 2. Understand useful work and total work. 3 Understand mechanical efficiency. (2) Ability goal 1. Learn to attribute from physical phenomena and experiments..

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"Exploring whether using machinery saves work" Machinery and Work PPT Courseware 2 Preview Tips 1. What are the two necessary factors for doing work? for example. What are the formulas and units for calculating work? 2. What are useful work, total work and extra work? 3. What is mechanical efficiency? count..

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Update Time: 2024-11-18

This template belongs to Physics courseware Beijing Normal University eighth grade physics volume 2 industry PPT template

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