The hot molecules around the heat source expands, becomes less dense, then rises. When it rises, the cooler molecules moves down to take its place. This can occur in fluid, which include gas or liquid.
Answer:
thermoset
Explanation:
A thermoset material is a polymer that is irreversibly hardened by curing. Curing is induced by heat and cannot be undone because the polymers cross link during the process, creating permanent chemical bonds.
Explanation:
A molecule can be made up from same or different elements. Whereas a compound will have different atoms.
Therefore, the difference between a molecule and a compound is that a compound is made up of atoms from different elements.
For example, 
is a molecule and NaCl is a compound.
And a chemical change creates a new substance.
The radiations detected by Arno Penzias and Robert Wilson
were the original heat from the Big Bang.
Today, we call those waves the "Cosmic Microwave Background".
I'm not sure, but I think those guys were awarded a Nobel Prize in Physics
for that discovery.
