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. Momentum is the mass multiplied by the velocity, so when the rod gets smaller at the top, the velocity must get greater to keep the same momentum (conservation of momentum). The fisherman gets the original momentum when he flicks his wrist unleashing all of the potential energy in to the rod to send the fly to its final location.
Greig Spolek, a professor at Portland State University, set up a test using a high-speed camera and a strobe light. He tested many different rods, from the original wood rods, to the more modern graphite ride. He took pictures to analyze the strength of the rods (to hold the fish), and the frequency of the motion to find the speed of the rod and ultimately to find how far the fly will go.
He also tested rods with the same stiffness, but made from different materials, to find which on will send the fly the farthest, yet still be strong enough to hold the fish.
Even though Spolek understands how fly-fishing works (the frequency, the stiffness, the air resistance, the lengths, the materials) he and other scientists have yet to come up with an equation to make “the perfect rod”.
Rist, Curtis. “Angling for Momentum”. Discover. September, 1999