My brother tried to kill me?

my brother is 10 i am 13.Ok so my brother was wacking me with a big stick and i grabed it and threw it out a window and all of a sudden he started going crazy.he was pinning me down and choking me and saying "YOU DESSERVE TO DIE!" and then i pushed him off and he was like.IM GETTING A KNIFE TO KILL YOU! and them he came out with a huge steak knife.i ran into my dad's room and all he said was "knock it off josh" THATS ALL!!!! and i can't call the police because my mom will be mad.she NEVER gets josh in trouble and i called her today and was like "he was joking" but HE WASNT this isnt the first time. a few days ago it was scissors, and yesterday is was a box cutter! im seriously scared.i wanna go live with my gramma but my mom said no and if just call my gramma and she picks me up i will get in trouble and my mom will just pick me back up! i don't know what to do.I'm not running away because i have no where to go and if i live with my friends there parents will drop me off! i dont know what to do!!! please help and im NOT the type of person to commit suicide btw.i sooo scared! helpp