Originally Posted by NutLoose
Depends how many layers deep too
That's avery good point. As ever, it's what we don't know that matters.
As we should expect from a Met wallah,
langleybaston also makes a very good point. Pingpong balls have sufficient diameter to leave open surface gaps if in a single layer. We also need to know the thickness and coefficient of conductivity of the pingpong ball's shell, its radius, and the dryness of the gas (air?) it contains. Ballance that against the coefficient of radiance of the water.
Physics is our friend; it lets us fly (except bloody Gravity).