The stream of water flowing at high speed from a garden hose pipe tends to spread like a fountain when held vertically up, but tends to narrow down when held vertically up, but tends to narrow down when held vertically down. Explain how?

Explanation

As the stream falls, its speed `upsilon` will increase and hence its area of cross-section a will decrease, ac cording to equation of continuity, i.e., `aupsilon = a consta nt`. That is why the stream will become narrow.
When the stream will go up, its speed will decrease, hence its area of crosssection will increase, ie. it will become broader and spreads out like a fountain.