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

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

discuss:

1. What is the principle of measuring the mechanical efficiency of a pulley block?

Measurement principle: h=Whave/Wtotal=Gh/Fs

2. What physical quantities need to be measured to measure the mechanical efficiency of the pulley block?

G ---- gravity of the object

h ---- the height of the object raised

F ---- Tension force at the free end of the rope

s ---- distance moved by the free end of the rope

3. What equipment is needed to measure the mechanical efficiency of the pulley block?

Scale, hook code, spring dynamometer, pulley block, iron frame, etc.

Experimental steps

1. Measure the gravity G of the hook code and record it in the table

2. As shown in the picture, install the pulley block and scale, and read the positions of the hook code and spring dynamometer from the scale.

3. Pull the spring dynamometer at a constant speed to make the hook code G rise at a constant speed. Read the value of the pulling force F shown on the spring dynamometer. Read the rising distance h of the hook code and the distance S moved by the free end of the rope from the scale. Record the data in a table.

4. Calculate the total work, useful work and mechanical efficiency

Exchange and discussion

1. What should you pay attention to when improving the hook code?

To increase the hook code at a uniform speed

2. When the same pulley block is hung with hooks of different qualities, will the mechanical efficiency be the same?

Not the same, the greater the hook code quality, the higher the mechanical efficiency

3. When two pulley blocks A and C are hung with the same hook code, are the mechanical efficiencies the same?

Not the same, the more moving pulleys, the lower the mechanical efficiency

Mechanical efficiency and calculations

Example 1: The mechanical efficiency of machine A is higher than that of machine B, indicating ( )

A.A’s useful work is more than B’s

B. To do the same total work, A’s useful work is less than B’s useful work

C.A’s total work is less than B’s total work

D. To do the same total work, A’s useful work is more than B’s useful work

Example 2: Use a horizontal pulling force of 10N to pull a car with a weight of 60N forward 3.5m on a horizontal road. The work done by the pulling force is ______J, and the work done by gravity on the car is _____J.

Variation training

1. As shown in the figure, an object with a weight of 100N is pulled by a horizontal force F and moves 5m to the left at a constant speed on the horizontal ground. The friction force on the ground on the object is 20N, then ( )

A. The work done by gravity is 500J

B. The pulling force is 100N

C. The pulling force is 120N

D. The work done by the pulling force is 100J

2. Xiaohan fetched water from the first floor of the school and walked up to the third floor at a steady speed. The height of each floor is 4m. The total weight of water and bucket is l0N. After going up to the third floor, walk horizontally for 100 meters at a constant speed to reach the class. Then the work done by Xiao Han on the bucket during this process is ____ J.

3. If someone uses a force of 100N to push down the end of the lever's power arm by 2 meters in the vertical direction, and the other end of the lever lifts a 320N weight 0.5 meters, then the useful work he does is _____J, the lever's Mechanical efficiency is _____.

Summary of this lesson

Measurement principle: h=Whave/Wtotal=Gh/Fs

G ---- gravity of the object

h ---- the height of the object raised

F ---- Tension force at the free end of the rope

s ---- distance moved by the free end of the rope

Experimental equipment: scale, hook code, spring dynamometer, pulley block, iron stand, etc.

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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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Update Time: 2024-11-18

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