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Mr.Mallon MMXVI

Mr Mallon is a Fellow of the Optoelectronics College
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Special Relativity

As far as the train passengers are aware they are sitting still and watching the outside world speed by.

Imagine that the train is moving at a constant velocity of  40 ms-1

A passenger can get up and walk down the train with a velocity of 5 ms-1.

What would be the velocity of the passenger as measured from a stationary person standing watching the train go by?

Its all relative!

The train has a velocity of 40 ms-1.

The passengers are sitting or standing still. According to the bystander on the platform they have a velocity of 40 ms-1 relative to him (and the platform)

The passenger has a velocity of 5 ms-1 relative to the train.

The bystander measures the speed of the passenger as 45 ms-1 relative to the platform.

Key Words

Inertial reference frame