Well, if these were the only forces acting on it.

这个力，也就是平行於斜面的这个地心引力的分力。

So we would have a force of friction acting upwards.

所以应该有一个向上的摩擦力 对吧？

And at home, his security forces acted with just unrestrained violence.

在苏丹国内，他的安全部队经常进行无节制的暴力行动。

The security forces acted after Iraqi government troops left the posts.

这些安全力量在伊拉克政府军队离开据点后采取了行动。

We only have forces acting in this vertical direction.

现在考虑更多的例子。

There's the force of gravity acting on this block of ice.

有一个地心引力作用於此积木上。

NASA likes to call this condition “microgravity, ” since there are subtle forces acting on you.

美国航天局（NASA）喜欢称之为“微重力”，因为其实还有一些微小的力作用在你身上。

If there are no other forces acting on them, they'll accelerate toward each other until they meet.

如果没有其他的力作用在它们上面，它们就会相互加速，直至碰到一起。

This axis is determined by the main force acting on the object, which in this case is gravity.

这个轴是由作用在物体上的主要力决定的，在这种情况下就是重力。

In either of these situations, there must not be any unbalanced force acting on them.

在任何一种情况下或者肯定没有合力。

The government can only do so much to reduce the powerful gravitational forces acting on a fragmented national industry.

政府能做的只有减弱作用于这个支离破碎的民族工业的强大地心引力。

Other forces act on moving objects, as well, like friction and air resistance, counteracting gravity, making this acceleration hard to see.

当然也有其他的力作用在移动的物体上，如摩擦力和空气阻力，它们抵消了部分引力，使这种加速度很难被察觉。

That type of behavior is very concerning and we hope to see Iran's naval forces act in a more professional manner.

这种挑衅行为令人极为担忧，我们希望伊朗海军舰队行事风格更为专业。

Forces accelerate objects, so the longer the force acts, the more the object's velocity changes — in this case getting faster.

力使物体加速，所以力作用的时间越长，物体的速度变化就越大——在这个例子中，就是速度越快。

Newton's law of universal gravitation, which had stood uncontested for over two centuries, depicted gravity as a force acting between two bodies.

牛顿的万有引力定律在两个多世纪以来一直没有受到争议，它将引力描述为作用在两个物体之间的力。

One of Newton's laws of motion says that something in motion can't just stop itself unless an opposing force acts upon it.

牛顿运动定律之一说，运动中的物体不可能自己停止，除非有一个相反的力作用在它上面。

But the main force acting against the ball is the air molecules that are pushing against it as it flies through the air.

但是作用在球上的主要力是空气分子，当球在空气中飞行时，空气分子推动着球。

So let's look at the first scenario, we have a 5 N force of gravity acting towards the centre of the earth.

现在考虑更多的例子。

" Their structure can be disrupted when the force acting on the individual 'sand particle' is larger than their mutual gravity, " he added.

" 当作用在单个‘沙粒’上的力大于它们的相互引力时，它们的结构可能会被破坏，" 他补充说。

27. Until an external force acts, the system remains in equilibrium.

27. 在外力作用之前，系统保持平衡。