A moving train fills the frame of a shaky video. A ladder looms, and hands grip the rungs. A blur of movement, and you're inside an open train car piled with coal, trees whipping by on either side.

A Moving Reference Frame. Now suppose I take that ball on a train traveling at 10 meters per second (22.4 miles per hour). ... Bob is standing on the side of the tracks ...

Around 15 train cars came off the track and were resting on their top or side. He also shared that no hazardous materials spilled or were leaked, and there were no injuries.