"What is called work" mechanical work and mechanical energy PPT courseware

Description

"What is called work" mechanical work and mechanical energy PPT courseware

learning target

1. Be able to name the two necessary factors for doing work.

2. Be able to judge whether force is doing work on an object. (Key point)

3. Be able to use the work calculation formula to perform simple calculations. (Difficulty)

In life, we often see the phenomenon shown in Figure 11-1-1. A person pushes a cart and the cart does not move, and the stone does not lift. Although the person tries his best and sweats profusely, from a physical point of view, he does not Do work. So, what is the meaning of "work in physics"? How to judge whether force does work on an object? How to calculate the amount of work? This is the problem to be solved in this lesson.

collaborative inquiry

1. Comparing the concept of work and the two necessary factors of work, please list some examples of work. Compare which group lists more.

2. Discuss "Activity 2" on page 3 of the textbook, study examples of force not doing work, summarize several situations in which force does not do work, and list several examples of force not doing work.

Answer: There are three situations in which force does not do work on the object: ① The object is not acted upon by force, but it passes a certain distance due to inertia, that is, there is distance and no work (no work, no work). ② The object is acted upon by force, but does not move distance, it is impossible to move a distance in the direction of the force, that is, there is no effort (no effort). ③ The object is acted upon by the force and moves a certain distance, but the distance moved is not in the direction of the force. (the direction in which the object moves is perpendicular to the direction of the force), that is, the force has distance but no work (work without success).

3. Xiao Ming places a physics textbook weighing 3 N on a horizontal table, and pulls the textbook horizontally and uniformly with a horizontal pulling force of 1 N, so that it moves 0.5 m. Then the gravity of the textbook will do _________J, and the horizontal pulling force will do work _________J.

4. As shown in Figure 11-1-2, it is a school bus specially used to pick up and drop off students. If the mass of the vehicle reaches 1×104 kg, the resistance encountered by the car when traveling at a certain speed is 1% of the total weight. At this speed When traveling 1 000 m, how many joules of work does the engine do to overcome resistance?

Solution: G=mg=1×104 kg×10 N/kg

=1×105 N

f=0.01 G=0.01×1×105 N=1×103 N

W=Fs=fs=1×103 N×1 000 m=1×106 J

In conclusion

What have you gained from studying this lesson? Please summarize it in your favorite way (such as block diagram, list, knowledge tree) so that you can share it with your classmates.

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Update Time: 2024-09-09

This template belongs to Physics courseware Guangdong and Shanghai Edition Ninth Grade Physics Volume 1 industry PPT template

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