scout
He doesn't. Atticus compares the men in the mob to animals.
Tom is in the Maycomb County Jail during the time that Atticus faces the mob downtown.
Scout recognized Mr. Cunningham in the mob and engaged him in conversation about his son, which humanized Atticus in Mr. Cunningham's eyes and helped diffuse the situation. This act of empathy and understanding ultimately led to the mob dispersing and Atticus being saved.
Atticus explains the concept of a mob to his children by describing it as a group of people who act emotionally and without thinking rationally. He emphasizes the importance of maintaining one's individual conscience and not succumbing to group mentality. Atticus uses this example to teach Scout and Jem about standing up for what is right, even when others around you are behaving unjustly.
To protect tom from the mob!
I know the answer to the first part of the question. He compares the mob to wild animals. So it took an eight-year-old child to bring 'em to their senses, didn't it?" ... "That proves something-- that a gang of wild animals can be stopped, simply because they're still human." .. Sorry if it wasn't much help ):
Because Atticus was trying to defend Tom Robinson and protect the mob from causing harm to him. They even had to change him to another jail because of the people of Maycomb trying to get at him. (They weren't so much after Atticus as they were trying to get him out of the picture, in order to hurt Tom Robinson...) I hope this helps a little :)
The children, Scout and Jem, intervened and approached the mob at the jail where Atticus was guarding Tom Robinson. Scout's innocent conversation with Mr. Cunningham, one of the mob members, and her recognition of other men in the mob led them to disperse and retreat. Her presence humanized the situation and prevented any violence from occurring.
The children hear Heck Tate asking Atticus if the mob is gone. Heck Tate is the Maycomb sheriff who tries to maintain order during the tense situation outside the jail where Atticus is protecting Tom Robinson.
In "To Kill a Mockingbird," Scout unknowingly diffuses the tension during the mob scene at the jail by recognizing Mr. Cunningham and engaging him in conversation about his son, Walter. This interaction with Scout reminds Mr. Cunningham of his humanity and the respect he has for Atticus. This ultimately leads him to disperse the mob and prevent any harm to Atticus.
Atticus sits by the jailhouse to protect Tom Robinson from a lynching mob. He knows the mob is coming to harm Tom, so he positions himself there to prevent any violence from happening. It showcases Atticus's commitment to justice and doing what is right, even in the face of danger.
Jem didn't do anything, he just brought scout to the jail while the mob was there. Scout showed the mob that Atticus helps everyone. The mob wanted Tom Robinson, but they would have to go through Atticus (hurting him in the process most likely) to get to Tom. If Jem didn't bring Scout, Atticus would have been injured in some way.