The venturi-meter works on:

Water from a tap emerges vertically downwards with an initial velocity of $4 \,m/s$. The cross-sectional area of the tap is $A$. The flow is steady and the pressure is constant throughout the stream of water. The distance $h$ vertically below the tap,where the cross-sectional area of the stream becomes $\frac{2}{3} A$,is (take $g = 10 \,m/s^2$): (in $\,m$)

At what speed will the velocity head of a stream of water be equal to $40 \ cm$ of $Hg$ (in $cm/sec$)?

Water is flowing steadily through a horizontal tube of non-uniform cross-section. If the pressure of water is $4 \times 10^4 \ N/m^2$ at a point where the cross-section is $0.02 \ m^2$ and the velocity of flow is $2 \ m/s$,what is the pressure at a point where the cross-section reduces to $0.01 \ m^2$?

Bernoulli's principle is based on the law of conservation of