If you connect the body to a spring, which is neither compressed nor extended, there's no force acting on it.

如果将一个弹簧连在这个物体上,弹簧既没有被压缩也没有被拉伸,也不会有力作用在它上面

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If it's positive, it means you've stretched it, if it's negative, it means compressed.

如果它为正值,就说明弹簧被拉伸了,如果它为负值,就说明弹簧被压缩了

耶鲁公开课 - 基础物理课程节选