Kicking a shuttlecock can be considered a simple yet interesting sport. Archaeologists have found images of people kicking shuttlecocks on Han Dynasty portrait bricks, indicating its long history. The traditional method of making a shuttlecock is to wrap a copper coin or a coin in cloth as the shuttlecock base, cut off one end of a hollow goose feather tube and cut four slits on the other end, fold them outward at 90°, and sew them onto the shuttlecock base with thread, then insert five or six roosters' feathers. A beautiful shuttlecock is thus made. Although the structure of the shuttlecock is simple, there are various ways to kick it, and many places also hold shuttlecock-kicking competitions to see who can perform the most spectacular and difficult moves. However, why must the shuttlecock be equipped with feathers? Can a shuttlecock without feathers still be kicked? An experiment will show that only with feathers can the shuttlecock in the air maintain the position of the shuttlecock base facing downward, and each kick of the foot will coincide with the landing of the shuttlecock base. If the feathers are removed, the shuttlecock will tumble in the air and cannot guarantee that the foot will hit the shuttlecock base accurately. Therefore, the function of the feathers is to maintain the stable position of the shuttlecock in the air. The shuttlecock base concentrates almost all the weight of the shuttlecock, and although the feathers are light, their area is much larger than that of the shuttlecock base. When the shuttlecock flies in the air, the air resistance on the feathers is much greater than that on the shuttlecock base. If the shuttlecock tilts to one side, the air resistance acting on the feathers will pull the shuttlecock back to the position where the shuttlecock base is directly below. In terms of mechanical analysis, although the weight of the feathers is small, when they deviate from the equilibrium position, the air resistance torque generated by the feathers is very large, making the shuttlecock return to the position where the shuttlecock base is directly below.
Not only the shuttlecock, but also arrows and badminton shuttlecocks use feathers to maintain stability. However, the feathers used in arrows and badminton are much harder than the roosters' feathers used in the shuttlecock. Because the flight speed of arrows and badminton shuttlecocks is much faster than that of the shuttlecock, compared with the soft feathers of the shuttlecock, hard feathers can produce a stronger aerodynamic effect, and the longer arrow shaft also provides a longer lever arm for aerodynamic force, making the stabilizing effect more effective. The stabilizing effect of aerodynamics is also applied in modern warfare. All non-rotating projectiles, such as mortar shells, rockets, and airdropped bombs, are equipped with tail fins. The function of the tail fins is to move the aerodynamic force point of the projectile to the rear of the center of mass of the projectile, so that the overturning moment is transformed into a restoring moment, producing the same stabilizing effect as the shuttlecock, arrow, and badminton shuttlecock.