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Sphere anemometers are simple devices that use the wind drag force on a sphere
to determine the wind speed by equating the weight of the sphere with the drag
force in a pendulum like configuration. Modern versions of this device use
ping-pong balls. By measuring the angle of deflection of the ball one can
measure the wind velocity.
There are 4 STL's files available with different scales:
m/s (two scales: engraved and 3d) knots (engraved) mph (engraved)
There's no need for a conversion table to measure the wind velocity.
The dots on the scale are 5 degrees apart. Note the two vertical dots at
More details here: http://www.diale.org/Ping-Pong-Anemometer.html
Materials and methods
Lets do some physics!
For large Reynolds number (https://en.wikipedia.org/wiki/Reynolds_number) the
drag coefficient for a sphere is about Cd=0.5. The typical mass and diameter of
a ping-pong ball is about 2.7g and 40mm, respectively, and thus with a
density of 0.081g/cm^3
The drag force is
Fd = 0.5 rhoair C_d A v^2
and the weight is
Fg=4 pi/3 R^3 g rhoball
For a given angle of deflection alpha one gets Fd=Fg tan(alpha) and thus
So by measuring the angle of deflection of the ball we can measure the wind
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