百科知识视频之煎蛋小学堂49 物理中常见的混淆概念[v]

Imagine learning for the first eighteen years of your life that the earth is flat,All through elementary school and high school you grow up,Hearing about the flat earth we live on,And doing boring flat-earth physics homework and then,If you're lucky enough you get to college and PSYCH!For the first time they show you a globe and say,"sorry for lying,the earth is actually round"Well this is unfortunately exactly what we do with。

想象一下你人生的头18年里一直学到的都是地球是平的 从幼稚的小学生一直成长到高中生 听到的都是我们生活的地球是平的 蛋疼的纠结着关于平面地球的物理作业 然后有一天你幸运的上了大学 我擦!他们第一次给你拿出了个地球仪 然后说 “很抱歉骗了你 但地球其实是圆的” 这是个残酷的真相 我们对引力的学习也是这样

1.Gravity：

一、引力

You probably learned that objects attract each other based on their mass,So you probably grew up thinking that light can't possibly be affected by gravity,Because light is massless,I know I did,Well guess what?The source of gravity is not mass!It's energy and momentum which light certainly has,Of course regular matter does too,So not only does light get bent passing by a star or planet or black hole.But light attracts the planet or star or black hole in return.To be sure,it's only a very very small amount,But a small amount is not zero,Anyway the point is that Newton's law of gravitation is just an approximation,Good enough to get us to the moon,but not perfect,General relativity is better.

或许你学过物体是因为质量而相互吸引的 所有长大后你就会纳闷光应该是不会被吸引的吧 应为光没有质量啊 我就是这么想的 可你猜这么着?引力的来源不是质量!是能量和动量 显然光也有这些 别的物质就更有了 所以不仅光在经过恒星，行星还是黑洞时会被弯曲 光反过来同样还会吸引行星，恒星还有黑洞 准确的说 这种吸引虽然很小很小 但小并不代表没有 所有重点就是 牛顿万有引力只是一个近似的法则 这足够人们登月用的 但并不是完美法则 广义相对论才更准确一些

2.Special Relativity：

二、狭义相对论

Speaking of the moon,you probably also learned that:If a sheep is moving 2 mph relative to a train,And that train is moving 2 mph in the same direction relative to the ground,Then the sheep is moving 4 mph relative to the gound,2mph plus 2mph equals 4mph,right? FALSE!Experments in special relativity have confirmed,That velocities don't simply add together,And so the sheep will in fact be moving Very very ever-so-slightly slower.than 4mph relative to the ground.

说起月球君 或许你会记起这道题：如果一只小羊相对火车的速度是2英里/时 而火车相对于地面也是2英里/时同向运动 则小羊相对于地面的速度就是4英里/时 2英里/时 +2英里/时 =4英里/时 ，对吧?错了!关于狭义相对论的实验已经证明 计算速度不能简单地直接相加 所有这只小羊相对于地面的速度实际上要比4英里/时 稍微小那么一点点点

And the formula that correctly predicts this deviation from just adding,the velocities is (V1+V2)/(1+V1×V2/C^2),It's not a very big effect,But then again,the earth looks pretty flat,doesn't it? But the earth isn't flat.If I walk 10,000 km away from my cat,And you continue on walking 10,000 km more,You're NOT 20,000 km away from my cat,You're just 12,750 km away.

而消除这种误差的准确叠加速度的 公式是(V1+V2)/(1+V1×V2/C^2) 虽然影响不大 但话说回来 地球看起来也和平面差不多是吧?但地球却不是平的 如果我远离喵星人走了10000千米 然后你继续又走了10000千米 你和我家喵星人的距离可不是20000千米呢 你们的距离只有12750千米

In fact:The farthest on earth you can get from ANYTHING on earth is 12,750 km,It's the "earthly distance-limit"Though we normally call it the diameter of the earth,And similarly when you try to add two velocities together,There's a "cosmic speed limit"of 300,000,000 m/s.That is the speed of light.

真相是 你能跑过地球上最远的一段距离不过12750千米 这是地球君的距离限制 也就是我们常说的地球的直径 同样的当你想要叠加两个速度的时候 有一个30亿米/秒的“宇宙速度极限” 这就是光速

So just because to our eyes the earth looks flat,Velocities look like they simply add together,And light looks like it doesn't attract gravitationally,Is that an excuse to mislead ourselves and our children,About the true nature of things? NO

所以我们能够因为地球看上去是平的 或者速度看似能简单地相加 又或是光线看起来没有万有引力 就可以找理由误导我们自己和祖国的花朵 不告诉他们自然的真相吗?不。