"Gong" Mechanical and Gong PPT Courseware 2

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"Gong" Mechanical and Gong PPT Courseware 2

1. Work in mechanics

A force acts on an object, and the object moves a certain distance in the direction of the force. The effect of this force shows results. In mechanics, it is said that this force has done work.

2. Two necessary factors for doing work

(1) Force acting on an object;

(2) The distance the object moves in the direction of this force.

These are two necessary conditions for judging whether work is done, one is indispensable!

"Two necessary factors" means "one cannot exist without the other"

1. Are you tired when you hold a stack of books without moving? Did you do your job? Why?

2. A football is kicked with the foot and the ball rolls on the ground. During the rolling process, does the person do any work on the ball?

3． When a person pushes a wooden box forward, does the box's gravity and supporting force do any work? Why?

Calculation of work

1. It is stated in mechanics that work is equal to the product of force and the distance traveled by the object in the direction of the force. That is: work = force × distance

If F is used to represent force, S represents the distance traveled by the object in the direction of the force, and W represents the work done by the force. That is: W=FS

The unit is represented by a symbol: 1J=1N·m

Meaning: If a force of 1 N is used to move an object 1 meter in the direction of the force, the work done by the force on the object is 1 Joule.

Example: Xiao Ming uses a horizontal thrust of 50N to push a box weighing 100N forward 10m horizontally. (1) How much work did Xiao Ming do on the box? How much work does gravity do?

(2) If Xiao Ming lifts the box 1.5m higher at a constant speed, how much work does he do?

Solution: (1) The work done by Xiao Ming on pushing the box:

W1＝Fs＝50N×10m＝500J

Work done by gravity:

W2＝Gh1＝100N×0m＝0J

(2) Xiao Ming’s lifting force on the box is equal to the gravity of the box

F＝G＝100N

The work done by Xiao Ming on the lifting force of the box:

W3＝Fh2＝100N×1.5m＝150J

Knowledge summary

1. Work:

(1) Concept: It is stipulated in physics that ___ acts on an object,

A force is said to have done work on an object by causing it to pass a certain distance in _______.

(2) Two necessary factors:

①__ acting on an object;

②The distance that the object passes through in _______.

(3) Three situations of no work being done:

①Powerful and without distance:

②There is distance and powerlessness:

③ There is a distance between force and force, but the direction of the force is perpendicular to the direction of motion of the object.

2. Calculation of work:

(1)Formula: W = Fs

(2) Unit of work: Joule (J); 1J=____N·m

3. The principle of work:

When using machinery, the work done by people will not be equal to the work done when not using machinery. That is to say: using any machinery cannot save work.

Classroom reinforcement exercises

1. Judgment of right and wrong:

1. When a weightlifter holds the barbell motionless, the lift does work.

2. A person lifts a heavy object and moves it at a constant speed in the horizontal direction for a certain distance. The lifting force does work on the heavy object.

3． When an apple falls from the tree, gravity does work on the apple.

4. The ball moves a certain distance on a smooth surface, and the support force of the table does work on the ball.

Research assignments:

Measure the work done by yourself as you move up the next floor

Require:

1. Measured:

(1) Weight;

(2) Floor height h

2. Calculation:

(1) The work done by going upstairs.

(2) The work done by going downstairs.

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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: 2024-09-28

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