I addressed these clocks earlier in the thread.2inq said:OK, to begin with, there is only one plane of reference on the ground. The laser beams located directly above each other, a single event takes place in spacetime as the various parts of the single tank ( bottom cleat, axel, and top cleat) all break the laser beams simultaneously in the ground frame. This event is when the front of the tank breaks the beams, starting all clocks, both on those on the various parts of the tank and those on the ground. question (1) Do you disagree that the beams were broken simultaneously and the clocks started recording time simultaneously?

Yes, the three clocks start simultaneously in the ground frame. Since they're in the same position in the direction of the tank's travel, they also start simultaneously in the tank frame and the upper tread frame.

Yes, that's correct.As the rear of the tank (the bottom cleat, the rear axel, and a cleat that has rotated directly above the centerline of the rear axel, the last cleat that can trip the laser) passes by the laser beams a second time, all clocks stop recording time. You stated all three ground clocks will record 11.7 ns between events, the breaking of the laser beams twice.

They would be incorrect, since they are calculating speed with tank-frame lengths and ground-frame clocks.We measured the length of the tank tread and distance between the axels as 20 feet while the tank was stationary on the ground. A normal person would calculate that the tank passed by the laser beams at 1.73c.

A smarter normal person would place two clocks a known distance aparton the ground (say 20 feet), synchronize those clocks using any method you like, then find the time (23.5ns) it takes the front of the tank to get from one clock to the next.

Then, they can correctly calculate the ground frame speed of the tank: 0.866c.

Using your setup, the ground observer can determine neither the speed of the tank nor its length. They can assume that the length of the tank is the same as it was when at rest, but why would they do that when with a little more preparation they can measure the speed directly and thus deduce the length?You say the axel distance and the bottom of the tread has physically shrunk to 10 feet. question (2) How does the ground observer, or the ground clocks, calculate this length? He has no idea how fast the tank is going, he is using his lasers to time the tanks passing. He doesn't know if the tank is travelling at 1000 miles per hour or .999c before he makes his timing measurements.