"Measuring the Mechanical Efficiency of Pulley Blocks" Mechanical and Work PPT Courseware 2

"Measuring the Mechanical Efficiency of Pulley Blocks" Mechanical and Work PPT Courseware 2

learning target:

1. Further understand the concepts of useful work, additional work, total work and mechanical efficiency;

2. Be able to use mechanical efficiency formulas to perform simple calculations;

3. Be able to measure mechanical efficiency and know how to improve mechanical efficiency;

Learning focus: Be able to use mechanical efficiency formulas to perform simple calculations.

Learning difficulties: Be able to measure mechanical efficiency and know how to improve mechanical efficiency.

[Preview independently and prepare carefully]

Knowledge review:

1. ___________ is called mechanical efficiency, and its formula is; ŋ=___=___. Because the useful work is ___ the total work, the mechanical efficiency is ___100%. (Fill in: <, >, =)

2. When using a moving pulley to lift a heavy object, the useful work is ______, the extra work is ______, and the total work is ____________.

[Independent exploration, cooperation and exchange]

Activity one:

In an experiment to explore the mechanical efficiency of a pulley block:

(1) In addition to hook codes, iron stands, and pulley blocks as shown in the figure, the experimental equipment used also requires __________ and __________.

(2) During the experiment, the hook code should be __________ when pulling the spring force to measure force.

(3) If the experimental device is as shown in the figure, the relationship between the distance s moved by the power F and the height h raised by the weight G needs to be calculated:

Picture A____________Picture C____________

(4) The physical quantity to be measured (and expressed with symbols) is:

a. Use a spring dynamometer to measure ______, ______.

b. Use a scale to measure ______, ______.

(5) Useful work W in the experiment =______;

The total work W=______, and the expression of its mechanical efficiency is ŋ=______.

[Practice in class, test and consolidate learning]

1. Use the pulley block shown in the figure to lift an object of weight G at a constant speed h. The distance moved by the rope is _______; the useful work done is ________; assuming the pulling force used is F, then the mechanical efficiency of the pulley block is _ ________.

2. It is known that n=2 of a certain pulley set. To lift a heavy object of 80N, a pulling force of 50N is required. To raise the object by 0.5m, what is the mechanical efficiency?

3. The picture shows the experimental device for measuring the mechanical efficiency of the pulley block. The total weight of the hook code is 6N.

(1) During the experiment, the spring dynamometer should be pulled vertically upward. It can be seen from the figure that the pulling force is _____N. If the hook code rises to a height of 8cm, the spring dynamometer moves upward _____cm. The mechanical efficiency of the pulley group is _ ____.

(2) If only the number of hook codes is increased, the mechanical efficiency of the pulley block will be _____.

(Optional: "Increase", "Decrease" or "No change")

[Consolidation after class]

1. Use the pulley block as shown in the figure to lift an object G weighing 480N at a constant speed. The pulling force F used is 200N. The time it takes to lift the heavy object 3 m is 10s.

Find: (1) The speed at which the weight rises. (2) The useful work done by the pulling force.

(3) The power of pulling force. (4) Mechanical efficiency of the pulley block.

2. A pulley block is shown in the figure. Its mechanical efficiency is 75%. How much pulling force is needed to lift a load weighing 3600N?

3. A classmate did an experiment to "measure the mechanical efficiency of the pulley block"

(1) In addition to hooks, iron stands, pulleys, and strings, the equipment used also requires ______ and _____.

(2) The principle of the experiment is _________.

(3) When pulling up the spring scale, the hook should make a ______ movement.

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For more information about the "Mechanical Efficiency of Mechanical and Dynamic Measurement of Pulley Blocks" PPT courseware, please click the Mechanical Efficiency of Mechanical and Dynamic Measurement of Pulley Blocks ppt tag.

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