tug of war
They could travel in opposite directions.
If it is facing in the opposite direction of travel it will slow down.
Rarefactions decompressions travel in the same direction, because sound are longitudinal waves.
The resulting phenomenon is known as constructive interference.
Probably not because you're still in the earth's atmosphere but I'm not sure
Earthquake waves travel in all directions.
to.....not travel???
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The train travelling opposite to the earth spin wear out first because it travel against centrifugal force.
rest
Up & down, there & back. Aircraft travel in all directions.
Light.