与电磁动量守恒

最近我发现一个有趣的问题虽然浏览一些互联网档案。从作者的“凯西和安迪,”他问道:“想象空间的电磁铁。非常强大,非常大。事实上,它重1000公斤,能够明显的磁场10光秒掉。有趣的是,有一块铁5光秒掉,也重1000公斤。把磁铁一秒钟。会发生什么呢?…磁铁获得速度向铁吗?如果是这样,它获得速度同时铁吗? ...If the magnet doesn't move, then [have you] applied a force to the magnet without a counter-force[?] ...You could argue that the magnet will move toward the iron 20 seconds after the magnet was turned on. In other words, the magnetic field moved out to the iron, then came back and pulled on the magnet. But that means the iron had a 10 second head start on the magnet. When they meet, they will cancel each other's velocities, but they will not be at their collective center of mass. They will meet closer to the magnet's starting point than the iron's starting point. In other words, the system's center of mass moved without force or counter-force." From what I've been able to research, gravitons and photons both travel at the speed of c. Electromagnetic fields such as light or magnetism are a function of photons. Thus, it seems like the lump of iron would accelerate first after 10 seconds when the magnetic wave reached it. Other than that, I'm not certain. My best guess is that since magnetism isn't reflected (as far as I know), the sheet of iron will move towards the electromagnet, impact it, and the resulting weight and motion will cancel itself out. Is that accurate, or what would actually happen?
——乔恩·w·(28岁)
美国罗彻斯特附近、锰

好问题。让我们选择一个明确的参照系,因为同时取决于我们选择的框架,我们不想意外开关的中间。重心将是一个方便的框架。

在t = 5 s,我们看到一些电磁干扰传播的磁铁,并推断必须开启在t = 0。在t = 15秒,我们看到铁移动,并推断出它在t = 10 s开始移动。我们看到没有磁铁的运动。所以如何动量守恒的呢?

答案是电磁场本身的势头。动量密度在任何地区的空间成正比ExB,在那里E电场和吗B是磁场。你可能想知道电场进入了故事,这是关于磁铁。麦克斯韦方程描述电磁场的空间/时间依赖性说改变B字段是伴随着一个E字段。

所以我们框架的总动量仍将是零。没有实际解决方程,我怀疑不对称设置将离开一点的电磁场动量传播到空间,所以总动量的磁铁(和电池等)和钢铁般的意志不加起来等于零。他们会朝着相反的方向的剩下的势头。

迈克·W。

(发表在11/10/2017)