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 分类： 把脉美剧气功

What?

(2020-11-22 17:14)
 分类： 费曼物理学讲义
https://mp.weixin.qq.com/s/t5HsuViDHkING0Bn9jd56g

(2020-11-19 16:08)
 分类： 费曼物理学讲义
https://mp.weixin.qq.com/s/52OBNyV1V8vfC-8Xr_6ZxA

(2020-11-16 16:57)
 分类： 费曼物理学讲义

5–5Units and standards of time 5-5 时间的单位和标准

We have implied that it is convenient if we start with some standard unit of time, say a day or a second, and refer all other times to some multiple or fraction of this unit. What shall we take as our basic standard of time? Shall we take the human pulse? If we compare pulses, we find that they seem to vary a lot. On comparing two clocks, one finds they do not vary so much. You might then say, well, let us take a clock. But whose clock? There is a story of a Swiss boy who wanted all of the clocks in his town to ring noon at the same time. So he went around trying to convince everyone of the value of this. Everyone thought it was a marvelous idea so long as all of the other clocks rang noon when his did! It is rather difficult to decide whose clock we should take as a standard. Fortunately, we

(2020-11-15 15:07)
 分类： 费曼物理学讲义
https://mp.weixin.qq.com/s/j1-7g_R4YDTazX-tzN_y8A

(2020-11-13 17:20)
 分类： 费曼物理学讲义
https://mp.weixin.qq.com/s/MBK9KEw9tYj-klB70s_X1A

(2020-11-11 17:19)
 分类： 费曼物理学讲义
https://mp.weixin.qq.com/s/La9fXYd9kin28kVUpCKNgg

(2020-11-10 16:38)
 分类： 费曼物理学讲义
https://mp.weixin.qq.com/s/zPWWf9J6PsXFzoiiTNN_pQ

(2020-11-09 17:45)
 分类： 费曼物理学讲义

4–4Other forms of energy 4-4 能量的其他形式

We can continue in this way to illustrate the existence of energy in other forms. First, consider elastic energy. If we pull down on a spring, we must do some work, for when we have it down, we can lift weights with it. Therefore in its stretched condition it has a possibility of doing some work. If we were to evaluate the sums of weights times heights, it would not check out—we must add something else to account for the fact that the spring is under tension. Elastic energy is the formula for a spring when it is stretched. How much energy is it? If we let go, the elastic energy, as the spring passes through the equilibrium point, is converted to kinetic energy and it goes back and forth between compressing or stretching the spring and kinetic energy of motion. (There is also some gravitational energy

(2020-11-06 18:36)
 分类： 费曼物理学讲义
https://mp.weixin.qq.com/s/jzyzLuQoTNmWaOtmC34ffA

(2020-11-05 17:04)
 分类： 费曼物理学讲义
https://mp.weixin.qq.com/s/8WeZaEgJG2m7njGxsoBJxQ