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Physics High

Understanding Simultaneity

Platform Observer Frame (Fixed Ground Viewpoint)
Interactive Viewport
Rear Wave front (Green)
Front Wave front (Red)
Ground Observer
Train Passenger

Simulation Controls

Train Velocity (v/c) 0.40 c

What to Observe

Simultaneous Strikes: Look closely at the ends of the concrete platform at t = 0.000s. Dual high-voltage lightning discharges strike the ground at the same instant.

Distance Recession: Notice how the train passenger moves directly away from the rear green pulse. This leaves the pulse to travel a much larger distance to reach them.

Oncoming Approach: At the same time, the passenger moves directly forward into the red light wave front, making contact over a noticeably shorter distance.

Stopwatch Results: While the platform clocks stops simultaneously at identical readouts, the train stopwatches show the time difference between the two strikes.