Jump to content
  • entries
  • comments
  • views

Physics Behind a Fly Fishing Cast

Sign in to follow this  



Anyone who is friends with me knows I love fishing of any kind. The one which I feel is the most labor intensive per cast is most certainly fly fishing, and know any of the friends I’ve taught even the most basic casts will agree. For those who aren't familiar with fly fishing, it separates itself from any other kind with the type of rod, reel, and cats the user makes. Regular fishing uses a reel where the user casts out in one fluid motion where they wish to go. In fly fishing, the flies, or baits, are so small that the caster needs to swing the line through the air in order to get it anywhere they want. So how are casts of over 100 feet possible with flies which weigh less than a gram? Well it is actually the same principle behind a whip.


A fly cast begins with a person raising the rod tip behind them while keeping tension in the line. Then the caster rockets their wrist forward. This flick of a wrist is all the momentum that is required to rocket the line forward. The small quick movement on the end of the rod translates to an incredibly fast traveling rod tip, acting like a lever arm spanning anywhere between 8 and 10 feet, resulting in a large amount of torque. Once the wrist has finished its flick around 1:30 position, then the momentum is transferred through the rod and to the rod tip which bends similar to a whip. The momentum doesn't stop there though, and this is the secret to a far reaching cast: the line. The momentum is transferred to the line which weighs considerably more than the fly itself in order to travel the needed distance. As the momentum travels from the fisherman’s arm, to rod, to line, the law of conservation of momentum applies. So, when momentum is transferred between each part the mass decreases, resulting in an increasing velocity of said part. By the time it reaches the end of the floating line to the leader, it is whippings through the air at incredible speeds. As mentioned before, this movement parallels the end of a whip.


This slowed down footage of a cast shows the momentum being transferred through all mediums in order to cast the fly.


So, while I can explain the physics behind a cast, I still can't explain why whenever I have the prime opportunity to cast towards a fish, my fly always ends up snagged in a tree. That though is a  problem to be solved another day. I'm guessing it's some kind of undiscovered attractive force between the two.


As always thanks for reading! - ThePeculiarParticle

Sign in to follow this  


Recommended Comments

So cool that you could relate one of your favorite hobbies to physics. :thumbsu:

  • Like 1

Share this comment

Link to comment

I've never tried this before but all the sudden I have a very strong urge to... 

  • Like 1

Share this comment

Link to comment

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Terms of Use

The pages of APlusPhysics.com, Physics in Action podcasts, and other online media at this site are made available as a service to physics students, instructors, and others. Their use is encouraged and is free of charge. Teachers who wish to use materials either in a classroom demonstration format or as part of an interactive activity/lesson are granted permission (and encouraged) to do so. Linking to information on this site is allowed and encouraged, but content from APlusPhysics may not be made available elsewhere on the Internet without the author's written permission.

Copyright Notice

APlusPhysics.com, Silly Beagle Productions and Physics In Action materials are copyright protected and the author restricts their use to online usage through a live internet connection. Any downloading of files to other storage devices (hard drives, web servers, school servers, CDs, etc.) with the exception of Physics In Action podcast episodes is prohibited. The use of images, text and animations in other projects (including non-profit endeavors) is also prohibited. Requests for permission to use such material on other projects may be submitted in writing to info@aplusphysics.com. Licensing of the content of APlusPhysics.com for other uses may be considered in the future.