## Wind speed calculation with an anemometer

1. The problem statement, all variables and given/known data

Hi everyone,

I'm currently in my first year of college and today I tried to calculate the wind speed of a fan by using a home made cup anemometer.

In our experiment we measured the time needed for 10 revolutions, on both of the speed settings of the fan. We then converted that to the number of revolutions per minute.

Then we calculated the circumference of a cup, and converted that to km. (to get the wind speed in km/h)

2. Relevant equations
Circumference = diameter * Pi

Finally, we multiplied the circumference in km with the number of revolutions per minute and devided this product by 60.

Now when we calculate all this we end up with a wind speed of around 0.0003 km/h .Now somewhere along the road we must have made either an error in calcutation or an error in reasoning, and we just can't find our mistake.

3. The attempt at a solution

These were our results:

http://www.scientificamerican.com/ar...ome-wind-speed
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Recognitions:
Gold Member
Homework Help
Hello and welcome to Physics Forums!
 Quote by tonykart44 Finally, we multiplied the circumference in km with the number of revolutions per minute and divided this product by 60.
If you are converting from revolutions per minute to revolutions per hour, do you need to divide by 60 or multiply by 60?
 Recognitions: Gold Member Homework Help In looking at your data, it seems to me that the circumference given below the speed 2 table has not been converted to km correctly.

## Wind speed calculation with an anemometer

We divided by 60 because the article said so, we didn't really question it because it made sense since there are 60 minutes in one hour.

However when I change it it gives me a more acceptable value of around 1.1 km/h for the lowest speed and 1.4 km/h for the highest speed. If we then take into account that we didn't factor in the friction of our meter and certain statistical errors, this looks like a much more acceptable value.

But I am still wondering, is 1 km/h not a little low? It is just a small table fan but this still appears a little low to me. Do you know of any reliable sources for commercial table fan wind speeds perhaps? (I've not been able to find one myself).

I also converted the second circumference correctly this time.

An updated version of the results: