Barrel Contents

There is a barrel with no lid and some wine in it. " This barrel of wine is more than half full," said George. Peter says, " No, it's not. It's less than half full." Without measuring the contents and without removing any wine from the barrel, how can they easily determine who is correct?

Answer:

Tilt the barrel until the wine barely touches the lip of the barrel. If the bottom of the barrel is visible, then it is less than half full. If the barrel bottom is still coverd by the wine, then it is more than half full.