英语中speed 和 velocity 有什么区别的?

英语中speed 和 velocity 有什么区别的?
我在澳洲学物理,这两个是分开的,不一样的意义的,但是中文翻译过来都是速度的意思..

我在别处找的,你看看
speed
[spi:d]
n.
速度,速率
Our speed averaged out at 50 km an hour.
我们的平均速度是每小时50公里.
快速,迅速
Everyone was surprised by the speed with which the dispute was settled.
每个人都为这一争端解决得如此之快而感到吃惊.
vt.& vi.
急行; 加速
He sped his car through the street.
他开车飞速地穿过街道.
vi.
超速行驶
Was I really speeding,officer?
警官,我真的超速行驶了吗?
用法词典
speed
来自古英语 sped >
同义词：velocity swiftness fastness speeding amphetamine pep pill upper rush hotfoot hasten hie race accelerate speed up quicken hurry zip
简明英汉词典
velocity
[viˈlɔsiti]
n.
速度
A bullet goes from this gun with a velocity of 3000 feet per second.
此枪射出的子弹,其速度为每秒3000英尺.
同义词：quickness speed swiftness