打邊爐都會遇到既情況

what is a meat ball make of? meat, corn starch, seasoning (salt, pepper, flavor enhancer etc) and the most import thing we are discussing here --- water.

when you boil it (heat up) in a hot pot, the meat will cook (from rare to "done"), molecular structure of corn starch change (well it is beyond the scope of this question), seasoning normally) will not be changed. but water will heat up and eventually reach it boiling point - 100C. unlike the soup can boil freely, it was trapped inside the meat ball, so when it boil, i.e. turn in to steam, it make the meat ball bigger in size (like blowing a balloon).

so bigger size, same weight result to a floating meat ball.

Raw meatballs have higher density than water and sink in water. When they are heated up, the air inside expands and their density decreases, so they float on the surface.

肉受熱應該係縮細而唔係膨脹o架啵..

因受熱後 , 體積膨脹 , 排出之水重量大於本身之重量 , 浮力增加 , 所以上浮 .