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Explain why, when moving heavy objects on rollers, the object moves twice as fast as the rollers. Try a similar experiment yourself.

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At Holborn underground station there is a very long escalator. Two people are in a hurry and so climb the escalator as it is moving upwards, thus adding their speed to that of the moving steps. ... How many steps are there on the escalator?

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Which Twin Is Older?

A simplified account of special relativity and the twins paradox.

Take a Message Soldier

Stage: 4 and 5 Challenge Level: Challenge Level:2 Challenge Level:2
Find the time taken for the messenger to march up to the head of the column, then add the time for him to march back. This is equal to the time taken by the column to advance a distance equal to the length of the column.