A heavy object, like a football player moving at a high speed, has a lot of momentum—that is, once he is moving, it is hard to change his state of motion.

一个重物有很大的动量，也就是说，比如一位高速移动的足球运动员一旦运动起来，就很难改变运动状态。

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If all the data fits in the cache, then the data is read from disk only once; after that, all requests are satisfied from the cache at memory speed.

如果所有数据都在缓存中，那么只需从磁盘读取一次数据；毕竟，所有的请求都可以用内存速度从缓存中得到满足。

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The vehicle must take off and land at an airport; once in the air, it can range 460 miles at a speed of 110 miles per hour.

这款飞行汽车必须在机场起飞和降落；一旦升空，它可以以110迈的速度最多飞行460英里。

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This put the NYSE, where prices tend to be good but execution is usually slow, on notice that it had to upgrade its electronic capability at once in order to speed up trades.

ECONOMIST: Buttonwood

Once the container is spinning at the correct speed (typically a few revolutions per minute), the mercury spreads out to form a layer less than a millimetre thick, and in such a way that variations in the thickness of the mercury layer compensate for the imperfect shape of the container.

ECONOMIST: Mirror, mirror

Once I parked the machine, I glanced at the trip speed registered on the dashboard: 208 mph (335 kmph).

FORBES: One Lamborghini, One Man, 200 MPH