Astronauts look weightless because they are in continuous freefall towards the Earth, staying aloft because of their horizontal motion.

宇航员表明上看起来是失重的，那是因为他们在不停地往地球方向做自由落体运动，而他们在水平方向上的运动又使他们保持着漂浮的状态。

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Skylifter plans to use several such drives to control the craft's horizontal motion and to aid a buoyancy-control system within the envelope in moving the vehicle up and down.

Skylifter计划使用数个上述装置来控制飞行器的水平运动，并在表膜层内置浮力控制系统来调节垂直升降。

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Skylifter plans to use several such drives to control the craft’s horizontal motion, and also to aid a buoyancy-control system within the envelope in moving the vehicle up and down.

Skylifter计划使用若干这种驱动器来控制飞船的水平运动，同时也辅助安装在气球内部的浮力控制系统操纵飞艇的升降。

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"It's a horizontal motion of two pieces of the Earth's crust on either side of a vertical crack in the Earth,"

VOA: standard.2010.01.13

But if I see you through the glass, the object is going on some trajectory, which has got both up and down and horizontal motion.

但是如果我透过窗户看到你,这个物体沿着某个轨迹运动,既有上下,也有水平方向的运动

耶鲁公开课 - 基础物理课程节选

Previously, many buildings were made of concrete slabs and beams, which are less able to resist the horizontal motion of a powerful earthquake, experts say.

WSJ: After China Quake, Efforts Turn to Recovery