568　rate，ratio，speed和velocity

① rate表示速度、比率等。

I read at a rate of 150 words a minute. 我每分钟阅读速度为150个词。

The interest rates of the state bank have been lowered six times recently. 国家银行的利率最近下调了六次。

② ratio表示比或比率，不表示速度。

The ratios of 1 to 5 and 3 to 15 are the same. 1与5之比同3与15之比相等。

③ speed是没有方向的速度，行驶速度。

The two trains didn't lower their speed along the rails when running in opposite direction. 这两列火车在相反方向沿铁轨行驶的时候没有减速。

④ velocity是技术术语，带方向性，也表示极高速。

The velocity of a missile is controlled from thousands of miles away. 火箭的速度在数千英里以外加以控制。

The two cars clashed and crashed with great velocity. 两辆高速行驶的汽车被撞得粉碎。