求翻译：弹性固体内，存在应变便产生应力；反过来，对介质内部施加外力则介质，将产生平衡施加的外力的内应力。实际上，介质中存在着两种力：体力和面力。是什么意思？

Elastic solid , there is a strain will produce stress ; conversely , external force is applied to the internal medium is the medium , the internal stress balance of the applied force .

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In the elastic solid, the existence strain then has the stress; In turn, to medium interior rate of head movement then the medium, will have the balance infliction external force internal stress.In fact, in the medium has two strength: Physical strength dough making strength.

Elastic solids, strain and stress, in turn, the media pushes the media, will lead to balance the applied forces of internal stress. In fact, there are two forces on the media: physical and surface strength.

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