Thearos wrote on May 7
th, 2009 at 10:49am:
One of the many sources showing that Greeks and Romans believed that the sling bullet went so fast it got hot (perhaps more likely to have been due to transfer to kinetic energy ?). Nice catch, any way, re disposition of psiloi.
Been quite intrigued by how often this notion of lead glandes melting comes up. It's almost certainly nonsense but I Googled the specific heat and melting point of lead to do some ball park calculations.
Apparently lead has a very low specific heat, ie it takes only a small amount of energy to heat it up. (Actual figures are, 0.16 J/g.degreeC for lead, whereas for water it is 4.2 J/g.degreeC) The melting point of lead is 327 C.
A 50 gram projectile moving at 60 m/s has 90 J of kinetic energy, so if all this was converted to heat it would raise the temperature of the lead by 11.2 degrees. (Note major correction if you read the original post where I forgot to divide by the mass.)
Of course the actual amount of KE converted to heat by friction with the air would be very small, perhaps 10 - 20%, and the air itself would absorb some of the energy, like blowing on something to cool it. However an impact with with a hard unyielding surface (like a shield) would cause a sudden rise in the glandes temperature as the remaining KE was dissipated and such a gland would more likely be recovered quickly. So, perhaps the lead gland would be perceptibly hotter after being thrown hard, at least for a short time.