A perpetual motion machine would have to be frictionless.

永动机只能是一种无摩擦力的机器。

youdao

With 3-dimension motion of the mid-body you can achieve frictionless lateral flexion with no movement in the gas springs.

中央部份可氖三维运动，让用者在不使用气压弹簧的情况下作无阻力横向屈曲。

youdao

There are moments here that are perhaps too ravishing for their own good the beauty of the domestic scenes inside the family hut is like an antidote to the brute facts of poverty and yet, finally, it is impossible not to be stirred by the fluid, frictionless travelling shots of Gebrselassie in motion.

NEWYORKER: Endurance