The Physics of Fishing and Rotational Motion

[tfl813]

Homework Statement

I am writing a large paper on the physics of fishing and would like to know what equation would prove the statement that a longer fishing pole would result in a higher velocity of the lure?

My physics book gives me a gamut of equations for rotational motion but I can't figure out which on applies to this real world situation.

Thanks!

 

[LawrenceC]

Is the lure being cast? Show us the gamut of equations.

 

[tfl813]

Yes, the lure is being cast. My original equation that I used for my rough draft was: rotational inertia= (1/3)(m)l^2. But that does not prove my statement at all.

 

[LawrenceC]

You know that the faster the lure is going when the line is released, the greater the distance it goes. So what equations apply to that situation.

 

[tfl813]

That isn't really the situation I need an equation for. I need one that is length dependent. Think of a catapult, I need an equation that would say the longer the arm the greater the velocity of the projectile. Except in this case the arm is the fishing pole and the projectile is a lure.

 

[LawrenceC]

That's what I'm steering you towards without telling you the answer. The velocity of the lure is rod length dependent. Obviously you require one that defines velocity.

 

[tfl813]

I looked in my physics book and none of them have ω and length. The closest thing is ω=(rotational displacement/time), but that clearly is not it. The other one is L=mvr, but I'm not sure if it would help me. Those two are the closest ones so whatever you're wanting me to find, I don't think is in my book.

 

[LawrenceC]

How about omega*R, where omega is rotational speed in radians/second and R is the radius? The simple formula gives the velocity at the end of the radius. So if you have a radius of 5 feet and a rotatonal speed of 1 revolution per second the tangential velocity is:

2*pi*5=10pi feet/sec

 

[tfl813]

Lawrence you're the man, that one was not in my book anywhere. If I have a 7ft pole and am holding it from the very end the whole length of the pole will act as the radius, correct? So r=7ft?

 

[LawrenceC]

That is correct if you consider the pole doesn't flex during the motion. The length of the pole is the radius.

 

[tfl813]

That's all I need, thanks for the help!

 

[Pkruse]

It is not a simple question of pole length. One the one hand we must figure the length, spring rate, and lure mass. One the other hand we must match all that to the skill and casting style of the fisherman, which is not purely rotational. The idea is to apply the greatest possible force over the longest possible distance without breaking the line.