At times-say, you're driving a screw into a piece of balsa wood-an impact driver acts just like a drill, quietly turning your fastener. But as resistance builds, a spring-mounted, double-headed hammer in the tool's nose cone winds up. When fully compressed, it releases, spins 180 degrees, and smashes against the chuck, creating a massive burst of torque. It's like rapping a wrench with a hammer 50 times a second to loosen a frozen nut. Let's see your drill do that.