Between a rock and a stone...

Listen to these words:

Feather ... Stone

Why does feather sound so light and floating? And why does stone sound so heavy?

How about Rock? It sounds hard. Even more solid than stone.

I guess that's why they say "Between a rock and a hard place." It sounds much worse than "Between a stone and a hard place."

Bombs

First of all, I want to know why these two words sound the same:

balm

bomb

I was looking for my lip balm and noticed the similarity.

The meanings are very dissimilar and so is the spelling....

What do they have in common?