"The Speed ​​of Work" Machinery and Human PPT Courseware 3

Description

"The Speed ​​of Work" Machinery and Human PPT Courseware 3

learning target

1. Understand the concept of power and be able to derive the concept of power through comparison.

2. Know the meaning of power units, and be able to form specific concepts and learn conversions between units

3. Be able to use the power formula to perform simple calculations

There is a pile of bricks on the playground that needs to be moved to the building under construction. How many methods can we use to move it?

Do both methods do the same amount of work?

What's the difference?

Thought exchange:

(1) Does the student do the same amount of work from the 1st floor to the 2nd floor as from the 2nd floor to the 3rd floor? (The floor height is the same)

Does it take the same amount of time?

(2) Does the student do work equally fast from the 1st floor to the 2nd floor as from the 2nd floor to the 3rd floor? Tell me what is your judgment method?

If the work done is the same, compare the time spent doing the work.

Thought exchange:

(1) Does it take the fat and thin students the same amount of time to go from the first floor to the second floor? Does it do the same amount of work?

(Same time, different work)

(2) Do fat students and thin students do work equally fast? Tell me what is your judgment method?

If the work time is the same, compare the amount of work done

How to compare work done quickly and slowly

How to compare the speed of exercise?

Method 1: The time taken is the same, the longer the distance the faster

Method 2: Travel the same distance faster and in less time

Method 3: Look at the distance traveled per unit time v=s/t

How to compare the speed of work?

Method 1: It takes the same time, and the one who does more work will do it faster.

Method 2: To do the same work, the one that takes less time will do the work faster.

Method 3: Look at how much work is done per unit time

Take a look below at some of the powers of people, animals and vehicles

The power of elite athletes for long-term exercise is about 70 W, and the power of short-term exercise can reach 1 kW.

The power of Shanghai Santana sedan is about 66 kW, and the power of Jiefang CA141 truck is about 99 kW.

The power of a horse pulling a cart for a long time is about 450 W

The power of Shaoshan type electric locomotive is about 4 200 kW, and the power of Dongfeng Type 4 diesel locomotive is about 2 646 kW

Class exercises

1. Xiaoqiang lives in Building 3 of Huayuan Community. After school, he went from the first floor to the fifth floor for 20 seconds. If the total weight of Xiaoqiang and his schoolbag is 400 N, and the height of each floor is 3 m, then his power to go upstairs is ____W.

2. Climb the stairs to see who has the most power. For this purpose, the physical quantities that must be measured during the activity are: ________, ________, ________.

3. The figure shows the relationship between work and time when two machines A and B with a certain power do work. It can be seen from the figure that the power of the machine is greater. If machines A and B do the same work, machine B will do the same work. The time is more ___.

4. The power of an ordinary person's heart to promote blood flow is about 1.5 W. Then the heart does ________ J in one day. This work can lift a person with a mass of 60 kg about _____ m at a constant speed.

5. It is the busy farming season, and farmland requires a large amount of irrigation water. If the water pump pumps 360 m3 of water to a height of 5 m within 0.5 h (g is 10 N/kg), the power of the water pump to do work on the water is at least ( )

A. 1.8×106 J B． 3.6×106 W

C. 10 kW D. 3.6×107 W

6. Regarding power, which of the following statements is correct ( )

A. A machine that does more work must be more powerful.

B. If the work time is short, the power must be high.

C. If the same work is done in a short time, the power must be greater.

D. None of the above statements are correct

Class summary

1.The physical meaning of power

Power is a physical quantity that expresses how quickly an object does work.

2. Concept and unit of power

(1) Definition: work done per unit time.

(2) Unit

SI unit: watt, symbol W

1W＝1J/s

Commonly used units: kilowatt (kW), megawatt (MW)

3. Calculation of power

Expression: Power=work/time, that is, P=w/t

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For more information about the PPT courseware "How quickly machines and people do work", please click the "How quickly machines and people do work" ppt tag.

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Update Time: 2024-09-09

This template belongs to Physics courseware Shanghai Science Edition 8th Grade Physics industry PPT template

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