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### Earth Science Unit - Make Your Own Anemometer

Week 5: We created an anemometer, which is a device meteorologists use to measure wind speed.

Materials
Egg Cartons or Small Disposable Drinking Cups
Tape
Straws
Thumb Tacks (push pins) or Sewing Pins
Pencil with eraser
Craft Sticks

First the straws were taped together at right angles.

Next a craft stick was inserted into an egg carton piece.

A skewer was used to make an initial hole. This could have been done with a nail or scissors just as easily.

Four egg carton/craft sticks were taped onto the ends of the straws ensuring that the cups all pointed in the same direction.

A thumb tack was used to poke a hole through the center of tape and straw and then a pin was placed through the hole and into the eraser of the pencil.

Finally the wind speed was measured. A marker was placed on one of the cups so the revolutions could be more easily counted. A timer was set for one minute and the revolutions were counted. Repeating the experiment several times, the results were averaged to 4 revolutions/minute.

Meteorologists measure wind speed in miles/hour. I asked the older kids how the measurements from the anemometers could be converted into miles per hour and let them think about it overnight. My 12 year old has covered the math skills required to perform this calculation, but my 10 year old has not. None the less, thinking about the conversion is an excellent brain workout in logical thinking.

To convert revolutions per minute to miles per hour the revolutions need to be changed into a distance of miles and the minutes need to be converted into miles. My son measured the distance between two cups and multiplied by 4 to find the distance traveled in one revolution. Then he asked me how to convert inches into miles. After telling him there were 63360 inches/mile he was able to determine that the wind speed was less than one mile per hour.

Here's what the conversion calculation looks like using the formula for circumference instead of my son's estimate:

This give the results in miles/hour. (d is the diameter of the anemometer).

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