A body at rest will remain at rest and a body in motion remains in motion at a constant speed in a straight line, unless acted upon by an external force.

若没有外力的作用，一个静止的物体会保持静止而一个运动的物体会做均速直线运动。

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Fluid motion caused by an external force such as gravity.

由重力等外力引起的流体运动。

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Its inverse force analysis is to find all equilibrium configurations when an external force ACTS on its moving platform.

其力逆解即给定作用于上平台上某点的外力，求系统处于静力平衡时的所有构形。

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It could be that being a risk-taker drives you to play more games, or that some external force makes you both play games AND be an unsafe driver.

FORBES: New Study Claims Gamers are More Unsafe Drivers

The problem occurs when external force causes a baby's head to take on an abnormal shape.

BBC: Molly Askam

The risk must be that whatever government emerges will only prove an interlude before a fresh crisis, in which external pressure once again is required to force Rome to confront the Italian economy's structural shortcomings, perhaps in return for a deal with the European Central Bank to support the government bond market under its Outright Market Transactions program.

WSJ: Post-Election Inaction Could Reawaken Crisis