I had a look at a huge windmill and was wondering how fast the blades are spinning. Obviously, the distance the blades make is different on the outside than on the inside. Is the speed of a rotating object always measured in rpm and not in mph?
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The tips of those blades are moving WAY faster than you suspect.
If you have only MPH then you need to know at what distance from the center that measurement was taken.
I was driving home the other day and notice that one of the turbines I passed took about 4 seconds to complete one revolution. From this it is easy to determine that in one minute the blade would make a complete revolution in 60/4 = 15 revolutions in one minute.
In one hour that would be 60*15 = 900 revolutions.
The average span (diameter) of a wind turbine in Europe is 113m or 370′. The circumference of a circle is pi*d so the tip of that blade travels pi*370′ = 1162′. 1162′ is .2201 miles (the blade tip is traveling almost a quarter of a mile with each revolution!)
In one hour the blade tip will travel .2201mi * 900 = 198.1 miles. So the tip of the turbine blade was traveling almost 200 mph! This is one reason they frequently kill birds.
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