Are only sedimentary rocks used for relative age determinations?

No. All rock types can be used, many principles also apply to igneous rock

diagram is missing, but i will try to explain your doubt.

answer:

amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.

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explanation:

wind is defined by the direction it blows from.   for example, a wind blowing from north to south is called a northerly wind.