Science Puzzle
The Bernoulli Constriction
Water flows steadily through a horizontal pipe that narrows in the middle section and then widens again. The same volume of water passes through every part of the pipe each second.
At the narrow section, the water must flow faster to keep up. What happens to the water pressure at the narrow constriction: does it increase, decrease, or stay the same?
The Answer
Decreases. This is the Bernoulli effect: in a flowing fluid, an increase in velocity corresponds to a decrease in pressure.
The water speeds up at the narrow section because the same volume must pass through a smaller opening per second. As it does, some of its pressure energy is converted into kinetic (motion) energy. The total energy of the fluid stays constant, but the balance shifts: faster flow means lower pressure.
When the pipe widens again, the flow slows and the pressure rises back to its original value. This principle is used in aircraft wings (which create a faster airflow over the curved top surface), carburettors, and the Venturi meters used to measure flow rates in pipes.
The principle: Bernoulli's principle. In a flowing fluid, higher velocity corresponds to lower pressure. Energy is conserved: speeding the fluid up converts pressure energy into kinetic energy.