电磁波，以光速传播，也就是30万公里，每秒。
Electromagnetic waves travel with the speed of light, which is 300,000 kilometers per second.
我说把地球看成一个每秒飞行500公里的飞船。
I say look at earth as a spaceship travelling at 500km a second.
光速比声速要快，为每秒钟30万公里。
Light travels faster than sound at the speed of 300,000 kilometres per second.
扩充的比率是几乎每秒一个公里。
假如小行星撞击地球，它们的平均撞击速度将达到30公里每秒。
If an asteroid hit Earth, it's average speed would be 30kilometers per second.
光以每秒30万公里的速度传播。
光每秒传播的距离大约是30万公里。
The distance (that) light travels in one second is about 300,000 kilometers.
光每秒传播的距离大约是30万公里。
The distance (that) light travels in one second is about 300,000 kilometers.
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