Is it normal for your mom to be this way?

I was in my room cleaning when I heard my ten year old brother crying in the kitchen. M mom was having him set up a display for her craft shows, and he was having difficulty getting to a place to plug something in. This led to my mom cussing him out loudly, and, a direct quote,"I will not tolerate this level of stupidity." She used to do this to me, too, and her insults heavily affected my self esteem. I walked into the kitchen to get some food, and she told him to get out of her sight until he was smart enough to do it. As soon as I left she called him back out of his room. I'm pretty sure parents shouldn't act like this.
My brother and I both have IQs of over 120, yet she treats us like dullards. She wonders why I'm so convinced I'm a useless idiot. My dad calms her down afterwards, but never comes to our side. Is this normal for a parent to do?