Short Riddles and Answers

Question: When you do not know what I am, then I am something. But when you know what I am, then I am nothing. What am I?

Question: You are in a car with some helium balloons and hit the gas. While you accelerate, which way does the balloon move?

Question: Twelve pears hanging high, twelve men passing by. Each took a pear and left eleven hanging there. How can this be?

Question: You got a trophy that was two feet tall and your friend got a trophy that was 1 yard tall. Did you get 1st or 2nd?

Question: What devours everything from birds, to tree, bats, and bees? Surrounds you wherever you are, and is always moving?