Hey Yellow,

An impact wrench is usally used in auto repair. It basically turns the socket with a repeated hammering action. All the force is twisting but can be very great. Some have adjustable torque. Operate in air. Great for loosening sticky/rusty nuts/bolts.
Look at www.Harborfreight.com I think that is correct...they have good cheep stuff!
Hope that helps.
Dustin