"Mechanical Efficiency" Machinery and Human PPT Courseware 3

"Mechanical Efficiency" Machinery and Human PPT Courseware 3

think

Using simple machines such as levers and pulleys can save labor. Does it save labor and work at the same time?

Let's see it experimentally

1. Using any machinery will not save energy.

Think about it:

Are there any ways to transport sand up to the third floor?

2. Useful work, extra work and total work

1. Useful work: work that is useful to people.

2. Extra work: work that people do not need but have to do.

3. Total work: the sum of useful work and extra work.

W total = W has + W amount

3. Mechanical efficiency

1. Definition: The ratio of useful work to total work.

2. Formula: η=Ｗuseful/Ｗtotal=Ｗuseful/Ｗuseful＋W extra

Discussion: Is mechanical efficiency always less than 1?

ＷTotal＞W is useful, so η＜1

Note: (1) Mechanical efficiency should be expressed as a percentage. For example, the efficiency of a certain machine is 0.8, which is 80%;

(2) η is a ratio and has no unit;

(3) Mechanical efficiency is always less than 1;

Mechanical efficiency of pulley (set)

(1) Mechanical efficiency of fixed pulley

eta=Gh/Fs=Gh/Fh=G/F

(2) Mechanical efficiency of the moving pulley

eta=Gh/Fs=Gh/2Fh=G/2F

(3) Mechanical efficiency of pulley block

W useful = Gh (lifting heavy objects)

W total=Fs

W extra = W total - W useful or W amount = G moving h, ignoring friction

4. Is mechanical efficiency always certain?

How to improve mechanical efficiency?

1. Increase the weight of objects

2. Reduce friction

3. Reduce the weight of the machinery itself

Summary

1. The use of any machinery is energy-saving.

2. Classification of work

Useful work: work that is useful to people.

Extra work: work that has no use value to people but has to be done.

Total work: the sum of useful work and extra work.

3. Mechanical efficiency

Definition: The ratio of useful work to total work.

Formula: η=Ｗuseful/Ｗtotal=Ｗuseful/Ｗuseful＋W extra

4. Mechanical efficiency is not certain.

Consolidate practice

1. Regarding mechanical efficiency, the following statement is correct: ( )

A. Mechanical efficiency is always less than 1;

B. The more work a machine does per unit time, the higher the mechanical efficiency;

C. The more work a machine does, the higher its mechanical efficiency will be;

D. The more labor-saving machinery, the higher the mechanical efficiency.

2. In order to improve the mechanical efficiency of the pulley block, the following is correct: ( )

A. Lift heavy objects at a fast and constant speed;

B. Lift the heavy object at a slow speed and at a constant speed;

C. Increase the number of rope strands that bear the weight of the object;

D. Make the pulley lighter and reduce the friction during the rotation of the pulley;

Keywords: Machinery and Human Teaching Courseware, Mechanical Efficiency Teaching Courseware, Shanghai Science Edition 8th Grade Physics PPT Courseware Download, 8th Grade Physics Slide Courseware Download, Machinery and Human PPT Courseware Download, Mechanical Efficiency PPT Courseware Download, .PPT format ;

For more information about the "Mechanical Efficiency Machinery and People" PPT courseware, please click the Mechanical Efficiency ppt Machinery and People ppt tag.

"How to Improve Mechanical Efficiency" Mechanical Work and Mechanical Energy PPT courseware:

"How to Improve Mechanical Efficiency" Mechanical Work and Mechanical Energy PPT Courseware 1. Useful work, extra work, total work Think about it: What methods can be used to transport sand up to the third floor? Question 1: Which work achieves the purpose of our work? Work done on a heavy object (sand). it works..

"Mechanical Efficiency" Simple Machine Work PPT Courseware 2:

"Mechanical Efficiency" Simple Machinery Work PPT Courseware 2 Three kinds of work of machinery To increase G, the pulley must also be increased at the same time. At this time, you have to overcome the gravity and friction of the pulley and do extra work, otherwise you will not be able to complete the task. This skill has no use value but has to be done. It is an extra skill...

"Mechanical Efficiency" Simple Machine Work PPT Courseware:

"Mechanical Efficiency" Simple Machine Work PPT Courseware Learning Objectives (1) Know the concepts of useful work, extra work, and total work; (2) Master the concept and calculation formula of mechanical efficiency; (3) Understand the methods of increasing mechanical efficiency. ... ... ... 1. Useful work and...