Light can behave in some surprising ways. This disappearing coin trick is a great experiment to show one of the surprising ways. If you don't know how this trick works, you might think it was magic. Try this light magic trick and amaze your friends!
You are seeing light change directions. If light just travels through one material, such as air, it travels in a straight line. But when light passes from one material to another, say from water to air, it changes direction. The light changes direction so much that the light bounces back into the glass. None of the light from the coin reaches your eyes, so it vanishes.