A windsock is a tube-shaped piece of fabric, open at both ends, that hangs from a pole and shows which way the wind is blowing. Picture a giant colorful sock flying in the breeze: when the wind blows, the sock fills with air and points in the direction the wind is going.

You'll find windsocks at airports, where pilots need to know wind direction and strength before landing or taking off. A limp, hanging windsock means calm air, while a sock stretched out straight and rigid means strong winds. Helicopter landing pads almost always have windsocks because helicopters are especially sensitive to wind conditions.

Windsocks also appear at construction sites, chemical plants, and anywhere else people work with aircraft or need to know about wind conditions for safety. Some fire departments use them to predict how smoke and flames might spread during wildfires.

The simple design works perfectly: wind enters the wide mouth of the sock and flows through to the narrow tail, making the whole thing point downwind, like a floating arrow. No batteries, no electronics, just fabric and wind doing exactly what physics says they should.