How Light Travels and Bounces

By the end of this lesson, you will be able to show and explain how light moves in a straight line and what happens when it hits different things.

Think about a flashlight in a dark room. When you turn it on, the beam shoots straight ahead. It does not curve around the couch to find you. Light travels in a straight line, which means it keeps going the same direction until something gets in its way. That is why you can see dust dancing in a straight sunbeam coming through a window.

Sometimes light hits something smooth and shiny and bounces off. This bouncing is called reflection. When you look in a bathroom mirror before school, light from the room hits your face, bounces off you, hits the mirror, and bounces back to your eyes. That is how you see yourself. A calm pond or a clean car window can reflect light the same way.

Other times, light passes into something clear, like water or glass, and bends. This bending is called refraction. Put a pencil in a glass of water and look from the side. The pencil looks broken or shifted, but it is fine. The light bent as it moved from water into air, so your eyes get a tricked picture.

Light can also be soaked up. When light is absorbed, it stops and does not bounce back or pass through. A black T‑shirt on a hot Texas afternoon absorbs lots of sunlight, and that energy turns into heat, so the shirt feels warmer than a white one. Thick curtains absorb light too, which keeps a room dark.

So light goes straight, then it can reflect, refract, or be absorbed when it meets an object.

Try it: If you shine a flashlight straight at a mirror hanging on the wall, is the light mostly reflected, refracted, or absorbed?