What is velocity of efflux of a liquid?

Explain why :

To keep a piece of paper horizontal, we should blow over, not under it.

Explain why :

When we try to close a water tap with our fingers, fast jets of water gush through the openings between our fingers.

Explain why :

the size of the needle of a syringe controls flow rate better than the thumb pressure exerted by the doctor while administering an injection.

Explain why :

A fluid flowing out of a small hole in a vessel results in a backward thrust on the vessel.