Learn to Estimate! How fast is a blender blade spinning?

A blender blade spins so fast you can't even see it. So how would you even begin to know how fast it's spinning? A bike blender offers a cool way to understand this. Join in and learn how to use common sense and math to make a reliable estimate.
Instead of focusing on something we can't even count, we begin by looking at what we can count: the leg. Comes in at about 120 pedal strokes per minute.
Next we examine the gear size difference from the big chainring to the small cog at the wheel and estimate the ratio at 4:1.
Next we confirm that by counting the wheel rotations for every pedal rotation: just over 4.
Great! Now we're up to 480 wheel rotations per minute (RPM).
Next we look at the power transfer from the wheel to the blender pitcher, and estimate the ratio by comparing the size of the wheel to the size of the roller.
Throughout the process we take weird / tricky numbers and round them to easier whole numbers so its easier to do the math on the spot.
So... 17 pedal strokes in a 10-second period becomes 20.
28" wheel diameter becomes 30"
Finally we do the multiplication and it looks like:
120 Pedal Strokes per minute * 4 = 480 wheel rotations.
Round to 500.
500