Once, there was a teacher who held a glass in front of his class. He asked his students,
"How much do you think that this glass of mine weighs? 100 grams, 200, 250?".
One stood up and answered, "Sir, we won't really know how much it weighs unless we weigh it."
The teacher said, "That's correct but I have a question, what would happen if I held it up like this?"