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各种旋转发球,是通过不同发球手法和击球部位,使球体在飞行中产生强烈旋转,从而改变原抛物线轨迹,攻击性较强的一种性能发球。发球时,手臂的动量作用于球体上,再加上击球瞬间手腕的推压动作,不仅使球体受到向前飞行力,也使球体产生旋转力矩。全手掌触球时,使作用力的方向通过球体的上半部,利用手各部触球先后次序给球皮以摩擦,再加之手腕的推压作用,于是每个着力点就会依次对球体产生旋转力矩,使球体呈上旋向前飞入对方场区。当飞行的球体呈上旋转动时,球体上面是向前移动,带动空气也向前移动,这样就和向后流动的空气相抵,使球体上面的空气流速减小,因而压力增大;而球体下面的流速由于球体的旋转而把空气带动向后流动,这样就和向后流动的空气方向相同,使球体下面的流
A variety of rotating service, is through different service practices and batting parts, the ball in the flight to produce a strong rotation, thus changing the original parabolic trajectory, aggressive performance of a service. Serve, the momentum of the arm on the ball, coupled with the instant impact of the wrist hit the ball, not only by the ball by the forward flight force, but also to produce torque ball. Full palm touch the ball, the direction of the force through the upper half of the sphere, the use of hand touch the order of the ball to the ball skin friction, coupled with the push of the wrist, so each focus will turn on the ball Rotate the torque so that the ball is on the opposite side of the field before spinning. When the flying ball is rotating, the ball moves forward and drives the air to move forward, so that the air flows backward and the pressure of air on the ball increases. The lower flow rate causes the air to flow backwards due to the rotation of the sphere so that it flows in the same direction as the air flowing backward so that the flow below the sphere