Answer to the science question!

Ok! After a search on yahoo, I've found the answer. It's not a very exciting answer, to be honest.

Here goes.

When the dry ice(frozen carbon dioxide) comes in contact with a metal surface,

the metal surface was at a higher temperature than the dry ice.

Therefore, this will cause a very rapid sublimation on the dry ice.

Since dry ice=CO2, alot of CO2 will be produced. Especially at the part where the dry ice is in direct contact with the metal surface.

As a result, the dry ice will be pushed off the metal surface, due to the huge amount of gas below it that's rising rapidly.

As soon as the gas below the floating dry ice rises and diffuses off into the atmosphere,

The piece of dry ice drops, of course. And produces a sound.

And this will cause it to touch the metal surface again, producing alot more CO2, etc etc, and the cycle continues again!

But of course, this process happens extremely quickly and repeats itself over and over again, producing the vibration and the rattling sound, until all the dry ice has been sublimated.

As to dry ice on plastic... I haven't found any answers on the internet yet.

Hmm. Plastic is a bad conductor of heat, right? okie wait ah lemme think...

so. Maybe the heat from the plastic doesn't go to the dry ice as fast as metal? (coz it's a bad conductor of heat, metal is a good conductor of heat.) Just think of yourself holding 2 identical spoons getting heated at the same end. One is made of metal, the other is made of plastic. Obviously, the hand holding the metal spoon will feel the heat much faster. ^_^

Not enough heat-->dry ice sublimes almost normally-->Not enough CO2 gas produced to push it off the spoon-->No rattling sound.--->No fun.

xinyi