The Physics of Fly-fishin’ What does it take to launch an ultra-light fishing line over 200 feet? A little physics and a lot of feel for the fishing rod, that’s what. The trick to doing good is to have the thinner, end of the line, land on the water first then the fly. The end of the line cushions the fly, having the effect that a fly is landing on the water, not a piece of nylon string. This may sound easy, but it’s a lot harder than it seems. Just getting it to go that far is like “pitching a cotton ball at major league speeds.” The design of the rods makes this almost impossible task a little easier. The key is momentum.