In sailing forums, people have amazing arguments about the use of water ballast in yachts - 'cos any fool knows water is no heavier than water so it obviously can't exert a downforce, right?
In motorcycling forums people will argue vehemently that raising your body above the bike by standing up on the footpegs will power the centre of gravity of the bike - 'cos it's obvious to any fool since your weight is then supported by the foot pegs rather than the seat, right?
But I never thought I'd see professional pilots arguing that the density of otherwise identical objects would not affect their terminal velocity!
I guess its a sort of second order "any fool" thing.
1) 'Cos "any fool" knows that heavy objects fall faster, right?
2) Except of course that "any fool" remembers Galileo and the cannon balls and knows that is wrong and that gravity acts at (~)9.8 N/kg on light and heavy objects alike, right?
1 N = 1 kg m s^-2 so 9.8 N/kg = 9.8 m/s^2.
Gravity is a force per unit mass, or an acceleration, while forces due to drag on identical shaped objects of different densities (and hence different masses) are simply forces which result in an additional acceleration which is dependent upon the mass.
Thanks for an entertaining read.
Last edited by nonsense; 30th Mar 2014 at 08:57.