The Physics Behind the Thumb Trick

Summary by Krater

This video examines fluid dynamics in pipe systems using a garden hose and other demonstrations to explain why putting your thumb or a valve over the end does not change the volumetric flow rate.

From the video

Answers: Does putting your thumb over the end of a garden hose make the water flow faster?

• pipe hydraulics
• volumetric flow rate
• Bernoulli's principle
• friction losses in pipes
• hydraulic grade line

What it concludes

• Putting your thumb over the end of a garden hose does not change the volumetric flow rate, but it does increase the water velocity by decreasing the area.
• Closing a valve or nozzle in a pipe system causes friction losses and energy loss, resulting in decreased flow rate and zero pressure at the open end.
• Frictional losses in pipes are proportional to velocity squared, meaning higher speed results in more losses.