Weed Whacker Physics

When you turn on a weed whacker, the lines have two forces acting on them. One is the spinning motion of the disc, and the other is the drag of the air. This causes them to bend slightly so that they don't come straight out of the disc. If you make them longer, there is too much drag and the lines start wrapping around the disk, but weed whackers have a built security measure to prevent this. There is a small blade inside the guard that trims the lines to optimal length, to prevent the system from crashing and to make it so you can whack the most weeds as possible.