白勇语法第二篇39题

In terms of physics, the characteristic feature of the roller coaster is that the cars' potential energy,gained through their being lifted by a chain drive through the Earth's gravity to the top of the first drop,has been converted to kinetic energy by the time the ride ends.

 不明白白勇的解释：

through the cars' being done by...表示被动动作产生potential energy逻辑意思变扭，不符合物理学原理。

我的理解是：车子的潜能通过being lifted by a chain drive获得，不知哪里逻辑变扭，求指教，谢谢！