The Definition of Radian Measure
thingiverse
A simple manipulative to demonstrate the definition of radian measure. The track is marked in multiples of the wheel's radius R, both with integers and multiples of pi/2. The wheel is notched to help you start at R x 0 with the "R" vertical. Rolling the wheel forward shows that a quarter turn of the wheel (marked on the wheel with a short tick) takes you to R x pi / 2; a half turn puts you at R x pi; up to a full turn at R x 2 x pi (or 2 x pi x R if you like.) The integer multiples of R give a feel for the size of one radian ~ a little under 60 degrees. This is a remix of my own "pi day" design "The Definition of Pi" which focuses on pi as the ratio of circumference to diameter.
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