A windsock will hang approximately 30 degrees below the horizontal in a wind of only ...

A windsock will hang approximately 30 degrees below the horizontal in a wind of only ...

• A. 6 knots
• B. 12 knots
• C. 3 knots
• D. 8 knots

Answer: (A)

The windsock’s angle is set by the balance between wind force on the fabric and gravity pulling the sock downward. When wind is light, gravity dominates and the sock droops; as wind speed increases, drag on the sock grows (roughly with the square of speed) and the sock rises toward the wind, making the angle below horizontal smaller. An angle about 30 degrees below horizontal corresponds to a light breeze, which in practice is around 6 knots. If the wind were weaker, the sock would hang more downward (a larger angle below horizontal). If the wind were stronger, it would straighten more toward horizontal (smaller angle below horizontal). So 6 knots best matches the observed 30-degree drop.

The windsock’s angle is set by the balance between wind force on the fabric and gravity pulling the sock downward. When wind is light, gravity dominates and the sock droops; as wind speed increases, drag on the sock grows (roughly with the square of speed) and the sock rises toward the wind, making the angle below horizontal smaller.

An angle about 30 degrees below horizontal corresponds to a light breeze, which in practice is around 6 knots. If the wind were weaker, the sock would hang more downward (a larger angle below horizontal). If the wind were stronger, it would straighten more toward horizontal (smaller angle below horizontal). So 6 knots best matches the observed 30-degree drop.