Betty Parris's actions seem mostly to be motivated by fear. In Act One, she only wakes up long enough to accuse Abigail of drinking "a charm to kill Goody Proctor," and then again at the very end of the scene to accuse townsfolk of witchcraft. She seems to fear that she and the other girls will be in a great deal of trouble for the things they did in the forest, and when she has another outlet for that anxiety and fear, she uses it. The stage direction says that she "call[s] out hysterically and with great relief" when she accuses them. This opportunity to scapegoat other women eases her fear and worry.
Mrs. Putnam is motivated by her desire to find out why she has lost seven out of eight babies. She admits that she sent her daughter to Tituba in order to conjure their spirits and find out what killed them. When she sees her daughter "turning strange" and "shrivel[ing] like a sucking mouth were pullin' on her life too," she panics and is willing to attempt anything to save her and find the cause of her terrible misfortune.
Mary Warren is motivated by concern for herself. She doesn't want to tell the truth about Abigail and the other girls lying because she is afraid that they will accuse her too. Though Proctor succeeds in getting her to testify against the others in Act Three, she ultimately turns on him when Abigail accuses her of sending out her spirit.
Giles Corey is motivated by his guilt for accidentally implicating his wife as a witch. In Act One, he asked Mr. Hale what to make of the fact that she reads all the time and that she hides her books from him. Further, he mentioned that he was unable to pray when she was in the house but when she left he could pray again. Later, in Act Three, his guilt compels him to storm the court with his evidence against Thomas Putnam in order to prove her innocence.
Rebecca Nurse is motivated by genuine concern and love. She is wise and understanding. She says, "A child's spirit is like a child, you can never catch it by running after it; you must stand still, and, for love, it will soon itself come back." She seems to intuitively understand that the children are fine and that, with time and love, they will be well. Further, she thinks it is dangerous to seek "loose spirits" and would rather they look to themselves for the cause of any of the town's problems.