Re: What would allow to solid lead balls to hit the ground at differnet time?

I think that the reference you have picked up concerns a well known story 
about Galileo dropping things from the Leaning Tower of Pisa. It was only 
ever a thought experiment. We know that because if he had ever actually 
tried it, it would not have worked out the way he wanted. The larger ball 
would have hit the ground first!

When you drop things from a high tower, they are subject to two forces: 
gravity, and air resistance. Gravity will produce a force that is 
proportional to the mass of the object, and therefore an acceleration that 
is independent of the mass. If gravity were the only force, objects always 
fall at the same acceleration (and therefore speed), regardless of their 
size. So if the experiment could have been done on the moon, where there is 
almost no air, lead balls dropped from the Leaning Tower of Luna City would 
have hit the ground at exactly the same time.

But air resistance affects objects in a different way. The force of air 
resistance is proportional to the square of the velocity, and to the size 
of the leading surface, for objects of the same shape. Now I am going to go 
into some slightly messy mathematics, which might be a little bit ahead of 
where you are at school.

If the radius of a lead ball is r
the density of lead is rho

then

mass of lead ball = volume * density = 4/3 * pi * r^3 *rho

force of air resistance = constant * leading area = constant * pi * r^2

acceleration due to air resistance = force/mass = constant/(4/3 *r *rho)

= new constant/ r

What that means is that the acceleration due to air resistance is inversely 
proportional to the radius of the lead ball. The smaller the lead ball, the 
more it will be affected -- slowed -- by air resistance as it falls.

(I have checked with the proprietor of Big Al's Pizza Joint in our suburb, 
and he assures me that it is not the custom for leftovers to be arranged in 
a leaning tower ;-)