"Power" work and mechanical energy PPT courseware

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"Power" work and mechanical energy PPT courseware

Review of the previous section

1. Work: A force acts on an object, and the object moves a certain distance in the direction of the force. In mechanics, it is said that this force has done work.

2. Two necessary factors for doing work

(1) A force acts on an object F

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

3. Calculation formula: W = Fs

In life, not only the amount of work done is important, but also the speed of doing the work is also important. How to compare the speed of work done?

Example 1: Students A and B carry the same bucket of water to the fourth floor. A takes 10 seconds and B takes 20 seconds. Who does the work faster?

To do the same work, the one that takes less time does the work faster.

Example 2: Both students A and B took 20 seconds. A carried two buckets of water to the fourth floor, while B only carried one bucket of water to the fourth floor. Who did the work faster?

In the same amount of time, the one who does more work does it faster.

1. Methods to compare work speed:

1. The same amount of time compared to the amount of work done: an object that does more work will do work faster.

2. To do the same work, compare the length of time: the shorter the time, the faster the work is done.

2. Power

1. Physical meaning: Indicates how fast an object does work.

2. Definition: The ratio of work to the time taken to do the work.

3. Formula: power = work/time

Numerically equal to the work done per unit time.

4. The unit of power: J/s, watt (watt) symbol W

1W=1J/s, 1kW=1000W, 1MW=106W

5. The physical meaning of W: 1W is 1J/S, which means that the object does 1J of work in 1s.

1. Power means _____ of work done. The greater the power, the more ____ of work done. The size of the power is determined by ____ and ___.

2. Trial judgment (P=W/t)

The more work A does, the greater the power ()

B has small power, which means less work is done. ()

The shorter the work time of C, the greater the power ()

If D does work quickly, the power will be high ()

3. For two machines, the power of A is 750 watts and the power of B is 2250 watts. The ratio of the work done by A and B in the same time is ( ); if the same work is completed, the ratio of the time taken by A and B is ( ). )

4. What does the power of 70W mean? Which one has greater power, 70W or 450W? Which one does the work faster? Why?

A power of 70W means that the machine has done 70J of work in 1 second.

450W is more powerful than 70W and works faster

450W＝450J/s, 70W＝70J/s

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Update Time: 2024-09-07

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 2 industry PPT template

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