So, a massless body cannot have a net force on it, because the acceleration of the rope cannot be infinite.

所以没有质量的物体不会受到力,因为绳子的加速度不可能是无穷大

耶鲁公开课 - 基础物理课程节选

If the two forces don't cancel, you have a net force.

如果这两个力没有抵消,便会有一个净作用力

耶鲁公开课 - 基础物理课程节选

So, when we get really close together, granted, there is a net positive negative charge with a Coulombic force of attraction.

当它们真正离得很近时，假设有一个带正负电的电荷,带有库仑引力。

麻省理工公开课 - 固态化学导论课程节选

I am going to say if that electron is to stay in its orbit, that is to say it doesn't flee the atom, it doesn't collapse under the nucleus then the sum of the forces on the electron must be zero No net force. And so that will be the sum of a dynamic force plus an electrostatic.

如果电子会保持在它的轨道上运行,既不脱离原子的话，它就不会由于原子核对它的吸引力而被瓦解掉,电子所受的合力一定为零,由于没有合力,所以电子所受力为动态力和静电力的总和。

麻省理工公开课 - 固态化学导论课程节选