Bouncing Light: The Science of Reflection

Stand near a mirror or think about the last time you saw your face in a window or a puddle of water. You could see yourself, even though you weren't touching the glass or the water at all! How does that happen? Light is doing something very clever — it is bouncing. In this lesson you will find out exactly how.

Light travels in straight lines, like a very fast invisible arrow flying through the air. When that arrow of light hits a surface, one of two things can happen: it can pass through (like through glass) or it can bounce back. When light bounces back off a surface, we call that reflection. Think of it like a tennis ball hitting a wall. If you throw the ball straight at the wall, it bounces straight back at you. Light does the same thing. The angle at which light hits a surface is exactly the angle at which it bounces away. Scientists call the bouncing-away direction the reflected ray. Not all surfaces reflect equally well. Smooth, shiny surfaces — like mirrors, still water, or polished metal — reflect most of the light that hits them. This is why you can see a clear image of yourself. Rough or dull surfaces — like a brick wall or a piece of wood — scatter light in many directions, so you cannot see a clear image. A mirror is the best everyday example. The mirror's very smooth, silvery coating means almost all the light bouncing off your face travels straight to the mirror and straight back to your eyes. That is why your reflection looks so clear. Here is a real-world observation you can try: go outside on a sunny day and hold a small mirror. Tilt it gently and watch a spot of light appear on a wall or ceiling. That moving spot is reflected light — you are redirecting the sun's rays just by changing the angle of the mirror.