Angle Grinder 10000 rpm

Can you explain how angle grinders can produce 10000 rpm's and the purpose of the brushes?

Angle grinders use universal motors. Take a look at the 'Universal Motor' section here for a quick description.

Universal motors are similar to wound rotor series connected DC motors. This is where the high speed comes from. It also explains the brushes.

Keith

You can also get those RPM's from permanent magnet motors, want to make a simple one look at this: http://www.evilmadscientist.com/article.php/HomopolarMotor