2、可以加的介词不同
jump down后面如果加个from的话用法就和jump off一样了，后面接主语发出动作的地点。
也就是说跳下悬崖既可以说jump off the cliff，又可以说jump down from the cliff。
jump的用法
1、释义
n. 跳跃；跳动；上涨
v. 跳越；暴涨
2、例句
1、用作不及物动词S+～(+A)
She jumped when she heard the news.
她听到那消息时,跳了起来。
2、用作及物动词S+～+ n./pron.
The stream was so broad that nobody could jump it.
小溪太宽了,没人能跳得过去。
3、用作名词 (n.)
The jump was a very difficult one.
这种跳跃是个非常难的动作。