Casting in the air, at the speed reached by a fisherman, there are no major differences between stone and lead. Personal tests showed that, lead has a slight advantage, probably due to better aerodynamics (approximately 3% longer castings). However, things are different in water (eureka!) because any given body immersed is uplifted by the same weight of the displaced water, so the differences in specific weight have a greater effect. A stone with a specific weight of 3.0 loses one-third of its weight and with the remaining two-thirds has to overcome the hydrodynamic resistance during sinking. A lead of the same weight loses about one-tenth of its weight, and with the remaining nine-tenths faces a much lower hydrodynamic resistance because the same weight in the lead is more compact.

For example: a stone weighing 39 g (Pic. B) immersed in water still has 23 g (Pic. C) for sinking, and a lead weighing 36 g (Pic. D) still has 32 g ( Pic. E) and being more compact is hydrodynamically more efficient. But this is not a problem: If you want a weight that sinks faster or is more stable in remaining on the bottom, then you just have to use a heavier stone – for example one weighing 60 g instead of 40 g.

Physics
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Bathilith