The Physics of a Fishing Reel

Home the rod, the line, the fish.
The reel is able to produce a fair amount of torque on the fish as well. The reel’s main function however is to produce a heavy frictional force on the spool of line so that when the fish changes direction and starts to take line back off the spool the fish must first overcome the static frictional force and then continue to battle the kinetic frictional force the reel is putting on the spool of line as it swims away. By continually changing the fish’s direction with the torque exerted by the rod the fish starts to become tired and will allow itself to be pulled in the direction of the torque placed on it by the reel. Once a halibut realizes that the surface is close it is likely to change direction if it is not too tired already and make a run for the bottom again. This is where we will start to consider how this torque is being applied to the fish in the first place. The line is being brought in by winding it around a spool through a line feeder that moves back and forth as the spool spins to ensure that the line is distributed evenly on the spool. The line feeder is designed to move the distance of the average diameter of the line in the time it takes the spool to complete one period. This way the line does not pile up on one end and the most line possible can be used on the spool. The fisherman is creating the angular momentum of the spool by turning the handle of the fishing reel. This handle can be thought of as a crank that is turning gears inside the reel that in turn transfer the rotational energy to the spool. Check out this high end Penn saltwater reel they named the Torque series.


















The equations that explains the static frictional force that must be overcome by the fish to start to take line off the spool is f_s^max=μ_sF_N and the equation that explains the kinetic frictional force the reel exerts on the line as the fish swims away is fk=μkFN. The constants for kinetic and static friction which are denoted μk and μs are determined by the drag which is a component on the reel which is set by the fisherman. The drag should be set according to how much to how much force the fisherman wants to able to exert on the fish through the line before the spool will spin. Remember that you are also exerting this force on the tension in your line and on the knot where your line is attached to your hook.