What Am I Riddles

Question: I can hurt and make people bleed when I'm on the dark side, but used in good ways and I can also help you. What am I?

Question: Four hang, four sprang, two point the way, two to ward off dogs, one dangles after, always rather dirty.

What am I?

Question: I am a teacher, yet I am not a human nor a robot.

Question: People pick me, and watch me until they give me power. Then they don't stare in my eyes. What am I?

Question: Once you are in my sight, you are gone in a flash, and people tend to use me for cash. I am often used as a dire assist, and people often believe that I cause harm, when I am but its catalyst. What am I?