Physics

1. why a billiard ball knocks another billiard ball and sets it into motion
2. why a wooden door expands in size on a humid day
3. why certain pitches of sound can break a glass vase
4. why primary colors, like red and yellow, combine to form secondary colors, like orange
5. why a pot of spaghetti boils at a higher temperature if salt is added
(blank - no answer)