I know that if the second mass moved faster than the first one, then the picture is completely wrong.

因为我知道如果第二个物体比第一个运动更快,那么受力图就肯定不是这样了

耶鲁公开课 - 基础物理课程节选

You take the third one, and you go from one to the other, and you see whether heat flows, when you touch one object, the middle object, between those two objects.

第三个物体就可以作为温度计,将它与第一个物体接触，再与第二个物体接触，观察它们之间热量流动的方向。

麻省理工公开课 - 热力学与动力学课程节选

The other one tells you 10 - T = 2a.

第二个物体告诉你 10 - T = 2a

耶鲁公开课 - 基础物理课程节选