A straw looks bent in a glass of water because of a phenomenon called refraction.
This effect is an optical illusion that happens because light bends when it passes from one medium (like water) into another (like air).
Here’s a simple breakdown:
- Light Changes Speed: Light travels at different speeds through different materials. It moves slower through water (which is denser) than it does through air (which is less dense).
- Light Bends: When light rays travel from the part of the straw that’s underwater, they move through the water and then exit into the air before reaching your eyes. As the light passes from the water into the air, it speeds up and bends.
- Your Brain is Tricked: Your brain assumes that light always travels in a straight line. It doesn’t account for the bending. It traces the bent light rays back in a straight line to a “virtual” position, which is different from the straw’s actual position.
This makes the submerged part of the straw appear to be in a different place, creating the “bent” or “broken” look at the water’s surface.