# Math, Physics, who needs it?

## 14 posts in this topic

Ok, this is for the mathematical types on this board. My friends have always told me that "I always want to know how things work", guess I still do.

I have been thinking about the total weight of a particular lure. Assume that we have two baits that are absolutely identical in size and shape...lets say for simplicity that these baits are 10" inches long. One is made from a very light wood, say basswood, another from a dense wood, perhaps hard maple. The basswood will be much lighter thus requiring considerably more weight to get it to sink but the hard maple starts out heavier. Assuming only enough weight is added to get the bait to sink, which bait will weigh the most?

I borrowed this from another site. Apparently it was Archimedes that discovered why ships float, this guy figured this out in the 3rd century!!

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Why Do Ships Float?

The Greek Mathematician and inventor Archimedes lived during the 3rd century BC. According to history he was in the bath one day when he discovered the principle of buoyancy which is the reason why huge Greek ships weighing thousands of pounds could float on water. He noticed that as he lowered himself into the bath, the water displaced by his body overflowed the sides and he realised that there was a relationship between his weight and the volume of water displaced. It is said that he ran naked into the street yelling "heurEka" which is where we get our word "eureka!" (I found it), Greek heurEka I have found, from heuriskein to find.

Archimedes continued to do more experiments and came up with a buoyancy principle, that a ship will float when the weight of the water it displaces equals the weight of the ship and anything will float if it is shaped to displace its own weight of water before it reaches the point where it will submerge.

This is kind of a technical way of looking at it. A ship that is launched sinks into the sea until the weight of the water it displaces is equal to its own weight. As the ship is loaded, it sinks deeper, displacing more water, and so the magnitude of the buoyant force continuously matches the weight of the ship and its cargo.

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Assuming all other things are constant, the two lures should weigh the same amount at the point of sinking....correct?

Jed

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I seem to remember something about volume being involved in this. I think given the same size of the mass, the lighter would have to be weighted to equal the weight of the heavier at the sinking point, so I think yes, so they would both have to be, say for instance 4oz given their particular size.

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Jed, that is very interesting.Here is a question I have as far as buoyancy goes.E-tex by itself does not float,but when its added to a bait, it makes the bait more buoyant.Has anyone else noticed this , or am I all wet?Is it because it adds more volume than weight? I have added a coat of e-tex to Jakes and they seem to rise to the surface much faster than before.I also had that problem while trying to make neutral buoyant baits,I get them weighted just right,then e-tex and now they are slow risers????

Tom

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Hmmm,

Bouyancy force = total volume of water displaced by object immersed in liquid = weight of displaced liquid

so bouyancy force will need exactly the same total weight to counter act each other for objects of the same volume. You're spot on Jed

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That's the way I see it too. So....whether we use a light wood or a heavy wood, a bait of equal size and shape will be roughly the same weight, interesting. But, we have probably all noted the difference in action of some woods over others. I personally have found that light woods with lots of weight have more life to them than dense woods with a little weight.......despite the fact that both baits weigh about the same. Archimedes was one smart dude, bet he could have built some damn good baits.

Jed

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But look at the concentration of weight on light wood Jed. On light wood we are concentrating the weight into a spot which affect the COG (centre of Gravity) and on denser (harder) wood it's distributed more evenly. That makes the diff.

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like Lapala said, on lighter woods most of the weight will be concentrated wherever you add the weight. The reason this provides more action is because the rest of the bait is easier to move. The ballast wieght provides a pivot point.

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Good point guys, interesting.

jed

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But look again at the x-ray of the HR glide bait and he's got weights distributed throught he length of the whole bait. Thoughts?

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Is not weight placement at various locations done to cause the bait to hold a certain position in the water?

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Lunge,

I tried that method of weighting several times on baits and it did work altho I didn't find the results to be worth the additional work. Jim of "castor baits" has torn down HR baits in the couple years and found that he no longer uses this method of weighting.......maybe he also found it to be too cumbersome. I have only owned one HR (shaker) and wasn't at all impressed by the action altho the vast majority of musky fisherman think otherwise. I have personally found body shape which includes thickness, height, taper, roundness, etc., to play a larger role than any other factor in determining lure action and width of glide.

Jed

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Jed, I agree completely. I'm not so sure th e boys are interested in the action rathre than the amazing paint jobs that Jim does.

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Lunge, Jim of HR baits is without doubt the finest painter I have ever seen.

Jed

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Yah, he does provide huge amounts of inspiration - and a healthy does of consternation too :-D