When in a flow do the streamlines, streak lines and timelines coincide?

In steady flow

Explanation:

As we know that flow maybe steady flow or maybe unsteady flow.In steady flow the properties does not change with time but on the other hand in unsteady flow the properties changes with time.Also in unsteady flow streamlines,streak lines and timelines all are different but on the other hand in steady flow flow streamlines,streak lines and timelines all are coincide.

answer:

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