Whip up a Wind Gauge

Whip up a Wind Gauge

Scientists use an anemometer to clock wind speed. This is an easy experiment that will give you an approximate wind speed reading. We suggest not using it for hurricane-force winds—it’s built using coffee cups, for goodness sake!

Materials

• Four small Dixie or Styrofoam coffee cups
• Coffee cup with lid (or a milkshake cup with lid)
• Ball-point pen (sharp enough to pierce Dixie cups)
• Small piece of scrap wood to hammer on
• Five wide “milkshake” straws
• Scotch tape
• Big nail
• Felt pen
• About a cup of sand
• Watch
• Fan (optional)

Instructions

1. Insert the end of one straw into the end of another straw. Do the same thing with two more straws. You will now have two “double-length” straws.
2. Use your two long straws to make an “X”(they should meet at their junctions). Use Scotch tape to hold your X together.
3. Use the pen to poke two holes near the base of a Dixie cup (see photo). Do the same to the remaining three cups.
Balloon Rocket Materials

4. Pass the end of a straw through the holes of a Dixie cup (it should fit pretty snugly). Do the same with the other three cups and straw ends. Turn the cups so they are all facing in the same direction around the “circle”.
5. Secure each cup to its straw end using Scotch tape.
6. Using your scrap wood—and with an adult’s help because it can be slippery—hammer the big nail through the centre of the X.
Balloon Rocket Materials

7. Fill up the coffee cup halfway with the sand. Put on the lid. Stick the remaining straw through the lid’s middle right into the sand so it sticks up straight.
8. Place your X onto the coffee cup by putting the nail inside the straw.
9. With a felt pen mark an X on one of the cups.
10. Place your wind gauge in the wind or in front of a fan.
11. Use a watch to count the number of times the marked cup spins around in one minute.

What’s Happening

You’re measuring wind speed in revolutions per minute (rpm). To convert to kilometres per hour, you first need the radius of your anemometer (the distance from the nail to the centre of one of the cups). The radius must be in metres, so if your radius is 9 cm, use .09 m. Now plug your values into this formula:
         rpm radius 377 ÷ 1000 = speed
     For example, if your cups spin around 100 times in one minute, and your radius is 9 cm, the calculation would look like this:
     100 .09 377 ÷ 1000 = 3.393 km/h