long与length的区别

long是形容词,和系动词、联系动词共同构成句子谓语.
length是名词,需要和介词in构成介宾短语才能和系词系动词共同构成句子谓语,表示和long时候基本相同的意思.
例：
The rope is 5 meters long.
The rope is 5 meters in length.