Physics of Dipnetting :: physics dip net netting

The Physics of Dip Netting Introduction to Dip Netting Dip netting for salmon in the Copper River is a lot of fun but is also a lot of work.ï ¿ ½ During the summer months salmon will leave their home in the ocean and travel upstream in the Copper River to spawn in its many tributaries.ï ¿ ½ Near the small town of Chitna the Copper River flows through a narrow canyon which greatly increases the speed of the river.ï ¿ ½ This makes it harder for the salmon to swim upstream.ï ¿ ½ However the canyon also creates back eddies near the shore in which the river will actually flow the opposite direction.ï ¿ ½ This is good and bad news for the salmon.ï ¿ ½ Good news because the back eddies are flowing the direction the salmon want to go which makes their trip a lot easier.ï ¿ ½ And bad news (from the salmons point of view of course), it makes the salmon easier to catch because the water is flowing the ideal direction for dip netters as shown in the pictures below. ï ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½ Notice that the back eddie makes it really easy for the dip netter.ï ¿ ½ If there was no back eddie the current would push the net the other direction, which makes dip netting a lot harder. The Physics The physics of dip netting is really quite simple.ï ¿ ½ All a person has to do is find a back eddie with a nice constant current and hold the net underwater in the hopes a salmon will swim into it.ï ¿ ½ The physics then becomes a static equilibrium problem which means that none of the parts are moving in any way either in translation or in rotation (applies only to reference frame used) (Halliday 307).ï ¿ ½ This is illustrated in the picture below. The dip net pole can be compared to a lever of class 1 and the lever principle can be applied, similar to the applet at http://www.walter-fendt.de/ph11e/lever.htm.ï ¿ ½ As stated in the applet from the Contemporary College Physics Simulation Library a lever is in balance if the total left side torque is equal to the total right side torque.ï ¿ ½ Applying that statement to the picture above the person must apply a much greater force on the pole in order to maintain torque equilibrium because the distance from the pivot point is much less than the distance from the force of the current to the pivot point.ï ¿ ½ This can be expressed mathematically. ï ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½ F1D1 = F2D2.ï ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½Ã¯ ¿ ½ ï ¿ ½(where F is each force, and D is the distance each force is from the pivot point)