I assume that you are asking about sexual intercourse and rape here. If so, the answer to this question depends on the state whose laws you are studying.
In years past, a lack of physical resistance was always taken as a sign of consent. A man could not, for example, be convicted of rape if the woman he was accused of raping had not physically resisted him. As the link below says, before the 1970s or so,
A man would not be convicted of rape of a competent woman unless she had demonstrated some physical resistance.
However, in the years since then, many states have changed their laws on this subject. In those states, the laws now say that a person can simply resist verbally. As the link says,
In the early 2000s in many states, the prosecution can prove lack of consent by presenting evidence that the victim objected verbally to the sexual penetration or sexual intrusion.
There is no rule at present that applies to all states. States may have their own laws on this matter, but there are still states where a lack of physical resistance is taken as consent. Once more to quote from the link
The states that have not eliminated physical resistance as a test for lack of consent have declined to do so for fear of convicting an adult who has sex with another adult without the knowledge that he or she is not consenting.
Even in such states, however, it is sometimes possible to get a conviction for rape when the victim has only resisted verbally. A lack of physical resistance is not a complete indicator of consent even in those cases.