Weathervane | Weather Science

Summer is more than half way through.

Soon it’ll be fall and the change in seasons is usually accompanied by curious questions about the weather. 

Since autumn is often windy, one inevitable question is:

Where does wind come from?

This question has two meanings: a) how is wind created? and b) which direction does the wind come from? 🙂

Let’s try to answer question b) by making a weather vane.

What you need

• pencil that has an eraser head
• a piece of square cardboard
• straw
• scissors
• scotch tape
• pin
• something heavy to hold the pencil steady and not blown away (e.g.a pot of dirt, a cup of pebbles, sticky clay, etc)
• plastic or paper plate
• compass
• marker

Steps

1. Cut an 1 inch slit in one end of the straw using the scissors.
2. Slide the square cardboard into the slit and glue it in place.
3. Using the scissors, cut the other end of the straw into an arrow shape.
4. Place the straw with the cardboard horizontally on your finger and adjust the position until it can balance without falling. Now your finger is supporting the straw/cardboard combination’s center of gravity.
5. Insert a pin through the straw’s center of gravity.
6. Push the pin into the pencil’s eraser head. Give a straw a small tap sideway and make sure that the straw can spin freely.
7. Place the pencil in/on the heavy object you had prepared so that the pencil can stand straight up.
8. Find a windy place. Using the compass and the market, find and write down the four directions, east, south, west and north.
9. Put the pot-and-pencil in the middle of the plate.

Why

When the wind hits the weather vane, the straw should spin around and then stay roughly in the same place.

The arrow end of the straw is then pointing at the direction where the wind comes from.

Since the cardboard end of the straw has a larger surface, it allows the wind to push around more than the smaller arrow end.

The wind pushes the cardboard to the direction it is blowing to, causing the arrow end to point in the direction where the wind is blowing from.

Look up the direction marked on your paper plate.

If the arrow is pointing to the east, then it’s easterly wind, if it’s pointing to the south, it’s southerly wind, etc.