Cruise control

Before you begin

• Familiarise yourself with what an anemometer (a device that can be used to measure wind speed) looks like. Seeing an example may help the group to follow the instructions.
• Familiarise yourself with wind speed calculations and how to find speed, distance and time.
• The anemometer requires wind to move the cups around. If you don’t have outdoor space at your meeting place, consider doing this activity during a camp or even a visit to an airfield.
• The long lengths of dowel need to be 14 inches.

Make an anemometer

1. Everyone should get into small groups. Every small group needs a pencil, five paper cups, two 14-inch lengths of wooden dowel, one short dowel, a ruler, marker pens, duct tape, and one empty drink bottle.
2. Use the pencil to mark out four holes on an upright paper cup.

This cup will become the centre of the anemometer. The marks should be evenly spaced around the rim, creating two sets of holes opposite each other. One set of holes should be 1 cm from the rim. The other set should be 2 cm from the rim so the dowels don’t block each other when poked through.

3. Use the hole punch pliers to make the four holes.
4. Use a ruler and pencil to mark the middle of the two 14-inch dowels. Also mark 1.75 inches (4.5 cm) from each end. This is where the centres of the outside cups will go.
5. Push the dowels through the holes in the cup, until the centre marks meet in the middle. There will be four equal ends of dowel sticking out from the cup.
6. Use marker pens to decorate one of the extra cups, so it is obviously different from the others.
7. Set out the four extra cups so they are lying down in a square around the dowels. The base of one cup should be near the rim of the next: no rims or bases together.
8. Use the pencil to mark a spot 1 cm below the rim of each cup, where the dowel will go in.
9. Use the hole punch pliers to make a hole in each cup.
10. Slide the cups onto the dowels with their centres over the marked points. Secure them in place with duct tape.
11. Use the short piece of dowel to carefully pierce the base of the middle cup.
12. Thread the short dowel through the hole until it meets the cross formed by the long dowels. Tape everything together. This will be the axis around which your anemometer will rotate.
13. Lift the anemometer up and put the end of the short dowel inside an empty drink bottle. The anemometer should now be free to rotate.

Work out your wind speed

1. Every group should take their anemometer outside and check the wind will turn the cups. If the bottle is unstable in the wind, use duct tape to secure it to a surface or add water or sand to keep it steady.
2. Every group should set up the anemometer and a timer. Someone should time 60 seconds, while the rest of the group counts each rotation of the decorated cup.
3. Use a calculator to work out the wind speed in miles per hour (mph).

If your anemometer uses the measurements suggested above, each rotation should equal 2.75 feet. To get miles per hour, take the rotations per minute and divide it by 32. So, if you counted 80 rotations per minute, your anemometer is measuring a wind speed of 2.5 mph.

Fly the coop

1. Every group should open up Google Maps and drop a pin somewhere.
2. Select ‘measure distance’ from the menu and measure the distance between two points. Everyone should try measuring long and short distances: how far it is from their current location to their home, compared with their home and their favourite holiday destination?
3. Every group should discuss what it means to have the wind ‘with or ‘against’.

Airports will constantly measure wind speed so that pilots know how difficult it will be to land or take-off, and also to know whether their speed will change as they’re flying. If the wind is blowing against them, they’ll slow down because of it. If the wind is blowing with them, they’ll speed up.

4. Every group should work out how fast a bird could fly against the wind, from their current location to one of their homes, using the wind speed they have measured.

• • The flight speed of an unladen European swallow is roughly 25 mph. To work out how fast it would fly against the wind, take away your measured wind speed from the flight speed. So, a 25 mph bird flying into a 2.5 mph wind would only be moving at 22.5 mph because of the wind.
  • Now, use Google Maps to measure the distance to your home. Once we know the speed and the distance, we can work out the time it would take to get there.
  • If your home is 0.5 miles away, and the bird’s groundspeed is 22.5 mph, divide distance by speed to get time: 0.022 hours. This is a strange way to measure it, so multiply by 60 to get the answer in minutes. The answer is 1.32, meaning it would take a bird about one minute and 20 seconds to fly half a mile to your home with a 2.5 mph headwind.

5. Every group should work out how fast they could get to one of their favourite holiday destinations by plane, flying with the wind, using the wind speed they have measured.

• • A Cessna 172 plane has a cruising speed of about 140 mph. To work out how fast it would fly with the wind, add the plane’s speed to the wind speed (142.5 mph).
  • Take the plane’s speed and divide it by a distance of 285 miles to a favourite holiday spot. This gives a flight time of 0.5 hours, or 30 minutes.