拉力是一种物体在空气中所受到的阻力，它能产生与球运行方向相反的作用力，减缓球的运行速度，而升力则是一种能使物体偏离直线运行轨迹的力。
Drag is the force of air resistance pushing against a ball's motion and slowing it down, while lift is a force causing a ball to swerve off a straight path.
宇宙中每一物体的每个引力都会对宇宙产生一个指向物体本身的拉力，就像在重力作用下，抛向空中的球会被拉回地面。
All the gravity of all the mass in the cosmos should have been pulling the universe back inward, just as gravity pulls a ball back down to Earth after it's been thrown into the air.
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