The stratosphere (/ËstrÃ¦tÉËsfÉªÉr, -toÊ-/) is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. About 20% of the atmosphere's mass is contained in the stratosphere.
The chainsaw is a highly effective and efficient tree and branch cutting power tool. It works with an engine, referred to as a power head; powering a metal chain, driven by a centrifugal clutch, with a chain moving around a groove in the guide bar at fast speeds.
The Clutch. If the chain on a chainsaw was directly connected to the engine, it would be very dangerous. The chain would turn as soon as the engine started. The clutch allows the engine to turn freely at low rpm [rpm=revolutions (turns) per minute] without moving the chain.