Answer:
What can be measured but not seen?
Come up and let us go. Go down and here we stay.
You need a key to receive an answer from me. The answer you'll find is straight from your mind. What is it?
Many have heard it, but nobody has ever seen it. It will not speak until spoken to. What is it?
We are five little objects of an everyday sort. You will find us all in a tennis court.
What did the baby corn say to its mother?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?