"Exploring - Does Using Machinery Save Work?" Machinery and Work PPT Courseware 3

Description

"Exploring - Does Using Machinery Save Work?" Machinery and Work PPT Courseware 3

teaching objectives:

(1) Knowledge goals

1 Know that even using machinery is energy-saving

2 Understand useful work and total work.

3 Understand mechanical efficiency.

(2) Capability goals

1. Learn to summarize simple scientific laws from physical phenomena and experiments, and try to apply known scientific laws to explain certain specific problems.

2 Through inquiry, cultivate students’ ability to explore physical laws.

(3) Emotional goals

1. Cultivate the team spirit of collective thinking during students’ collaborative experiments.

2. In the process of student communication and cooperation, a scientific attitude of mutual respect and truth exploration is formed.

3. Develop a scientific attitude of seeking truth from facts and respecting the laws of nature.

A heavy object weighing 100 N is lifted by a moving pulley with a pulling force of 60 N, so that the weight is raised 2 meters.

(1) How much work does the pulling force do?

(2) How much work will be done if it is lifted directly by hand?

S=2h=2×2m=4m

Machinery for W=FS=60N×4m=240J

W hand=Gh=100N×2m=200J

Why is the work done by actual machinery greater than the work done directly by hands without machinery?

Mechanical efficiency

The ratio of useful work to total work is called mechanical efficiency

formula:

Mechanical efficiency is generally expressed as a percentage and has no unit.

Look at the data just now and think about whether the mechanical efficiency will be greater than 1? Why?

The useful work is always less than the total work, so the mechanical efficiency is always less than 1

Discussion in the group:

Judgment: Is the following statement correct?

1. Machines that do more work and have high mechanical efficiency

2. The more total work done, the lower the mechanical efficiency

3. To do the same useful work, the less the extra work, the higher the mechanical efficiency.

4. When doing the same total work, the more useful work is done, the higher the mechanical efficiency is.

5. When different pulley sets are used to perform the same useful work, the mechanical efficiency must be the same.

6． Because useful work is always less than total work, mechanical efficiency is always less than 1

7． When the extra work done is constant, the less the total work, the higher the mechanical efficiency.

8. The greater the proportion of useful work in the total work, the higher the mechanical efficiency.

9. Mechanical power saving with high mechanical efficiency

10. Machines with high mechanical efficiency have a large ratio of useful work to total work.

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Update Time: 2024-11-03

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

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