Hobbies And Interests
Things You'll Need
Instructions
Build Your Anemometer
Use the protractor to measure and register four marks 90 degrees apart on the bottom of a cup. Punch holes on the round wall of the cup just above the bottom rim at each mark. Try to keep the holes exactly 90 degrees apart.
Punch a hole in the exact vertical middle of the wall of the remaining four cups. One of these is the off-color one. Use a ruler to make sure your holes are accurately placed.
Mark the exact center of the length of each straw.
Insert a straw into the hole of one of the one-hole cups. Bend it over about a half inch to the left inside the cup and staple it in place to the cup wall. Repeat with the second straw and another one-hole cup.
Thread the two straws through the holes of the cup with four holes so that they are perpendicular. Put the remaining two cups on the bare ends of the straws. Ensure that the cups all face exactly either clockwise or counterclockwise around the central cup.
Bend a half-inch of the loose end of each straw to the left and staple in place inside these last two cups.
Align the center points of the two straws inside the central cup. Double-check to make sure the cups are all symmetrically aligned. Flatten the straws at the center point and staple their overlap to the bottom of the central cup.
Push the needle through the flattened straws and the bottom of the cup on which they rest. Use a thimble if you must. Push until half the needle sticks out the bottom.
Ensure that the cup assembly freely rotates around the needle. Enlarge the needle hole if necessary. You may wrap some tape around the top of the needle to make sure it won't slip entirely through the hole.
Push the needle into the eraser of the new pencil. The eraser should hold the needle firmly while the cup assembly spins on it.
Using Your Anemometer
Measure the distance from the center of one rotating cup to that of its partner on the same straw. This is the diameter of the circle your anemometer travels. Multiply the diameter by pi (3.14) to get the circumference. If you used inches, divide by 12 to convert this to feet.
Take the anemometer into the wind. Measure how many revolutions per minute (RPM) it makes. You can easily count this by the rotations of the off-color cup you so cleverly used.
Multiply the RPM by the circumference to calculate the velocity in feet per minute at which your anemometer spins. This is a crude approximation of wind speed that ignores the force of aerodynamics and friction.
Securely attach your anemometer to a light but strong wooden extension at least four feet long (a broom handle works well).
On a windless day, have a friend drive a vehicle at a set velocity while you hold the anemometer and count the revolutions. Record the relationship of RPMs to speed of the car, which is the same as the speed of the air rushing by on a calm day. Do this for a number of speeds to create an accurate graph of anemometer RPM versus wind speed.
Place your anemometer where it will measure unimpeded wind. You can mount it on a pole to get the device clear of buildings and trees. If you hold it while you use it, make sure it is well above your head so that you don't interfere with the wind hitting it.