| 摘要 |
A fin has a blade provided with a hole and a one-way movable flap having a fixing edge connected to an inner margin of the blade and a moving edge overlapping an outer margin of the blade to close the hole on the blade. When a diver alternately sweeps two legs up and down under water, the movable flap on the fin worn on the upward swept leg is pushed downward by the resistance from the water to open the hole. The same resistance vanishes when the hole is opened, allowing the diver to sweep the leg upward with reduced effort. On the other hand, the flap on the fin worn on the downward swept leg is pushed upward by the resistance from the water to close the hole, allowing the diver to kick water more powerfully and advance more quickly.
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