Water Faucet

Water coming out of a sink faucet narrows as it falls. It does this because...

A) its speed increases as it falls

B) of surface tension

C) of air resistance

D) of atmospheric pressure

Solution: A, B, and D are all relevant. Gravity causes the speed of the water to increase as it falls. By the equation of continuity (Av = constant), the cross sectional area must decrease. Surface tension is required to pull the water together and prevent it from breaking into separate streams. Atmospheric pressure is required to prevent it from evaporating.