That frosty mug full of A&W root beer seems to drain so quickly. What seems like a lot of root beer is actually a lot of glass. The deception is uncovered when the root beer mug is placed in a tank of water. When looking at the mug above the water level, there appears to be a lot of root beer. But when looking at the mug below the water level, one observes the truth; the water surrounding the glass minimizes the effect of refraction and reveals the large quantity of glass. We've been deceived ... at least 'til now.
For more information about the physics of refraction and image formation, visit The Physics Classroom Tutorial - www.physicsclassroom.com/Class/refrn/index.cfm.