- 29,332
- 21,000
PS in this case, you can see that we have a common average velocity between all potential paths. And, any attempt to vary the velocity produces a greater increase in the action when ##v > \frac X T## than the reduction when ##v < \frac X T##. In other words, the ##v^2## term ensures that uniform velocity minimises the integral. Although, it's a bit more effort to prove that formally.