Question 4: You can squirt water over a greater distance by placing your thumb over the end of a garden hose than by leaving it completely uncovered. Explain how does it work?
Water can be squirt over a larger distance if thumb is kept on the opening of the hose. This can be explained by the equation of continuity.
According to equation of continuity,
Apply this equation to the squirting hose by assuming,
A1 = Normal cross-sectional area of the pipe
V1 = Velocity of water in the normal cross-sectional area A1
A2 = Cross-sectional area of the reduced exit
V2 = Exit velocity of water jet
Now see the above equation once again. A2 is smaller because the cross-sectional area has reduced by keeping thumb on it. This means the fraction is divided by a smaller number. This increases the quotient of the division which is equal to the exit velocity (jet). Therefore, if thumb is kept on the outlet of the hose, the outgoing water emerge with greater velocity and we can squirt water on greater distances.