"How to Improve Mechanical Efficiency" Mechanical Work and Mechanical Energy PPT Courseware

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"How to Improve Mechanical Efficiency" Mechanical Work and Mechanical Energy PPT Courseware

1. Useful work, extra work, total work

Think about it: What are some ways to move sand up to the third floor?

Question 1: Which work achieves the purpose of our work?

Work done on a heavy object (sand).

Useful work: work that satisfies our purpose of doing work and is valuable to us.

Calculation: W is useful

Question 2: What work is of no value to us, but we have to do?

1. Buckets, moving pulleys, bags, etc. also rise with the weight, which also lifts them. The work done to overcome these gravity

2. In addition, when the machine is running, there is friction to overcome the work done by the friction of the machine.

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

Counts as: W extra

Small exercises in class

1. When using a bucket to lift water from a well,

The useful work done is __________,

The extra work is __________,

The total work is __________;

2. If a bucket falls into a well and the bucket is fished out from the well, the bucket brought out contains some water. The useful work is __________.

The extra work is __________,

The total work is __________.

2. Mechanical efficiency

When the useful work is the same, would it be better to have more or less extra work?

Please calculate the percentage of useful work in the total work in several methods.

1. Mechanical efficiency: The ratio of useful work to total work is called mechanical efficiency.

2. Formula: η = W has/W total × 100%

eta is pronounced "eta"

3. η is generally expressed as a percentage and has no unit.

Small exercises in class

Please judge: Is the following statement correct?

1. The more useful work is done, the higher the mechanical efficiency ( )

2. The less the extra work, the higher the mechanical efficiency ( )

3. The slower the object does work, the lower the mechanical efficiency ( )

4． The more total work done, the lower the mechanical efficiency ( )

5. To do the same useful work, the less the extra work, the higher the mechanical efficiency ( )

6. When doing the same total work, the more useful work, the higher the mechanical efficiency ( )

7. The higher the mechanical efficiency, the more labor-saving ( )

3. Mechanical efficiency of some machinery:

When the useful work is the same, the mechanical efficiency is high,

①The total work is less (less gasoline is consumed, which has economic benefits)

②Less extra work (less waste, less car exhaust, social and environmental significance)

4. How to improve mechanical efficiency

Reduce machine weight

For example: the movable pulley is too heavy, making the two-moving and two-fixed pulley set very low. Its mechanical efficiency can be improved by replacing it with a lighter pulley.

Reduce friction between machines.

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Update Time: 2024-09-08

This template belongs to Physics courseware Guangdong and Shanghai Edition Ninth Grade Physics Volume 1 industry PPT template

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