"Gong" Mechanical and Gong PPT Courseware 4

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"Gong" Mechanical and Gong PPT Courseware 4

Pre-study tips

1. Is work in physics the same as what we usually call work?

2. Work in physics refers to ______________

3. The two necessary factors for doing work are ______________

4. The formula for calculating work is ________ and the unit is __________

Observe the following three pictures and discuss in groups: What common characteristics do their working processes have?

The concept of work: If a force is applied to an object and the object moves a certain distance in the direction of the force, we say that the force has done mechanical work on the object, which is referred to as work.

Work in mechanics includes two necessary factors: one is the force acting on the object, and the other is the distance traveled by the object in the direction of the force.

give it a try

Determine whether work is done.

(1) The weightlifter does not move while holding the barbell

(2) Xiao Ming carried his schoolbag and moved horizontally for a distance.

(3) When an apple falls from the tree, does gravity do any work on the apple?

(4) After the football was kicked out, it moved forward a few meters.

Answer after group discussion.

Estimate

1. How much work does it take to lift an egg 1 meter high?

2. How much work is required to lift a bottle of mineral water 1 meter high?

3. How much work does it take for a person to walk from the first floor to the third floor?

Communicate in the group and explain how to calculate.

Small exercise:

Student Chen Jie lifted the bucket with a mass of 10kg from a depth of 3m to the wellhead, and then walked another 20 meters in the horizontal direction. How much work did Chen Jie do on the bucket during this process?

Class summary

Looking back on this lesson, what did you learn?

What else have you gained from studying this class?

Classroom testing

Determining whether work is done:

a. Pull the object with a pulling force of 50N, and the object does not move. answer:_____.

b. Make your own ice cubes gliding at a constant speed on smooth horizontal ice. answer:_____.

c. Xiao Ming was sweating profusely while holding the barbell, motionless. answer:__________.

d. Lift a stone with force. answer:_____.

e. Use horizontal force to push the table. answer:_____.

f. An object weighing 50N moves horizontally at a constant speed under the action of a horizontal pulling force of 15N.

g. The football moved quickly on the field and finally stopped.

2. Fill in the blanks

a. The object has a weight of 20N and moves forward 2 meters at a constant speed under the horizontal thrust of 15N. The work done by thrust is _____J; the work done by gravity is _____J.

b. The mass ratio of objects A and B is 2:3. Under the pulling force of 30N and 50N respectively, they both move at a constant speed along the horizontal ground. The ratio of the distance traveled is 5:3. Then the pulling force does something to them. The work is _____.

3. Calculation

(1) Xiao Zhang is carrying a bucket of 80N water uphill. It is known that the length of the slope is 20m and the height is 4m. How much work does Xiao Zhang do? (2) Xiao Wang carried the same weight of water and moved 20m in the horizontal direction. How much work did Xiao Wang do? (3) Xiao Li carried an 80N bucket and stayed still for 5 minutes. How much work did Xiao Li do?

(2) In the school rope skipping competition, Wang Hong jumped 120 times in 1 minute, with a height of 5cm each time. It is known that her mass is 40 kilograms, so how much work did Wang Hong do during this rope skipping?

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For more information about the PPT courseware "Gong Machinery and Work", please click on the "Gong Machinery and Work ppt" tab.

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Update Time: 2024-11-25

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

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