"How to compare the speed of work" PPT courseware on mechanical work and mechanical energy

Description

"How to compare the speed of work" PPT courseware on mechanical work and mechanical energy

learning target

1. Understand the concept of power.

2. Know the calculation formula of power and the meaning of power units, and be able to calculate simple problems related to power.

3. Through the process of establishing the concept of power, the method of defining physical quantities using ratios is deepened.

4． Explain the meaning of power through examples and understand the important value of power in practical applications.

Core test point: Simple calculation of power

Preview before class

1. We can use two methods to judge the speed of work done by an object. The figure below shows the difference in work speed between digging soil with an excavator and digging soil manually. The judgment method used is: the work time is the same, and the amount of ______ is compared; Another way to judge is: if the work values ​​are the same, compare___________.

2. Power represents the _______ of work done by an object. The power of an object is 50W, which means ______________.

3. (2014·Nanchong) A worker uses a horizontal thrust of 50N to push an object weighing 200N at a constant speed on a level ground, causing it to move 10m in the horizontal direction in 20s. The power of the worker's horizontal thrust during this process is ______W.

4． A Dongfeng brand car travels at a constant speed of 160 m on a straight road, and the time it takes is 10 s. If the traction force on the car at this time is 5 000 N, then the work done by the traction force during this period is __________J, and the power of the traction force is It’s ______W.

Lectures in class

Knowledge point 1. Compare the speed of doing work

(1) If the work done is the same and the work time is compared, the shorter the time spent, the faster the work will be done, and the longer the time spent, the slower the work will be done;

(2) If the work time is the same, compare the amount of work done. The more work done, the faster the work will be done, and the less work done, the slower the work will be done.

[Example 1] In order to compare the speed of work, two students A and B competed to move bricks. The specific experimental process is as follows:

(1) Comparing the two pictures (a) and (b), we can get: ___________.

(2) Comparing pictures (a), (c) and (d), we get: ___________.

Knowledge point 2. Power

(1) In physics, the work done per unit time is called power. Power is a physical quantity that expresses how quickly an object does work.

Note: Power only reflects the speed of work done, not the amount of work done. If the power is greater, the work will be greater. This statement is incorrect and depends on time. On the contrary, if the power is greater, the power will be greater. This is also incorrect and depends on time. It can be seen from this that power is determined by two factors: time and work.

(2) The formula of power: From the definition of power, power = work/time. If P represents power, W represents work, and t represents time, then the formula of power can be expressed as: P=W/T

In-class testing

1. There are two machines A and B. The power of A is greater than the power of B. This means ( )

A． A must do more work than B

B． A must do work faster than B

C. A's work must take less time than B's

D. To do the same work, A will definitely take more time than B

2. The image of the work W done by two machines A and B changing with time t is as shown in the figure. It can be judged from the image ( )

A． A does more work than B

B． A does less work than B

C. A does work faster than B

D. A does work slower than B

3. Three students are going to have a building climbing competition to see who has greater power. They held the following discussion:

A: Comparison can only be made by measuring their respective weights, the time it takes to climb the stairs, and the height they climb;

B: When the time to climb the stairs is the same, you can compare them by measuring their weight and height of climbing the stairs;

C: When the height of climbing the stairs is the same, you can compare them by measuring their weight and climbing time. the correct one is( )

A． A, B and C B. A and B C. A and C D. B and C

4. Use two pulley sets (A) and (B) as shown in the figure to lift the object G weighing 400N by 10m at a constant speed in 100s. The weight of each pulley is 20N. Ignoring the rope weight and friction, during this process ( )

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"How to compare the speed of work" Mechanical work and mechanical energy PPT courseware 2:

"How to Compare the Speed ​​of Work" Mechanical Work and Mechanical Energy PPT Courseware 2 1. How to Compare the Speed ​​of Work Do cars and trains do work at the same speed? Which one does the work faster, man or crane? How did you compare? Doing the same amount of work takes different time...

File Info

Update Time: 2024-10-23

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

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