Einstein's theory of special relativity (A-level only)
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Motion depends on the frame

Motion depends on the frame

Platform observer and train passenger in different frames of reference with relative velocities labelled

A frame of reference is the coordinate system and clock an observer uses to measure where and when events happen. When you quote a speed, you are always comparing it with some frame, such as the road, the Earth, or a train carriage.

Einstein's theory of special relativity (A-level only) Lesson

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