What Am I Riddles

Question:

The dirtier I am, the whiter I get,
Leave a mark on me when you stand, I'll leave a mark on you when you sit.

What am I?

Question:

Take me for a spin and I'll make you cool,
but use me when it's cool and you're a fool.

What am I?

Question: You are my brother, but I am not your brother. Who am I?

Question: Each morning I appear to lie at your feet. All day I will follow no matter how fast you run. Yet I nearly perish in the midday sun. What am I?

Question: There are two sisters: one gives birth to the other and she, in turn, gives birth to the first. Who are the two sisters?