What is a tube of flow?

$A$ pipe having an internal diameter $D$ is connected to another pipe of the same size. Water flows into the second pipe through $n$ holes, each of diameter $d$. If the water in the first pipe has speed $v$, what is the speed of water leaving the second pipe?

$A$ horizontal tube of non-uniform cross-section has radii of $0.1 \,m$ and $0.05 \,m$ respectively at $M$ and $N$. For a streamline flow of an incompressible liquid, the rate of liquid flow is

In which direction is the velocity of a fluid particle at a point on a streamline directed?

$A$ pipe having an internal diameter $D$ is connected to another pipe of the same size. Water flows into the second pipe through $n$ holes,each of diameter $d$. If the water in the first pipe has speed $v$,the speed of water leaving the second pipe is

Two pipes of radii $2 \, cm$ and $4 \, cm$ are connected in series. What is the ratio of the flow velocities of the fluid in these pipes?