FACTUAL RIDDLES XVI

1. In scientific terms, what is the difference between hot and cold?
2. What is lighter when it's full and heavier when it's empty?

Answers:

1. Cold exists only in a relative sense. Temperature starts at absolute zero and goes up. Everything has heat, more or less.  

2. A helium balloon (Helium is lighter than air.) 

Credit #1:
GAMES Magazine
May, 1985
Alan Korwin