A body weighs less the farther it gets from the surface of t

further 是 更远的意思,修饰的是身体距地球表面的距离
这句话的意思是当一个身体距地球表面越远的话,它就越轻.
get 的意思我一时不知道可以用什么中文词来解释
总之,这句话可以这样说
A body weights less when it gets further from the surface of the Earth.
或者
The further a body gets from the surface of the Earth,the less it weights.
希望可以帮助你理解.