Matter is the stuff that makes things take up space.  Everything in the world is made of matter: you, cars, clouds, trees, orange juice, air, stars, hammers, everything.  When light hits matter it bounces off like a bouncy ball.  We only looked at one wave of light.  But all around you, there are many, many light waves bouncing off of everything. And they don't always just bounce.

Have you ever dropped a bowl of cereal and watched it go all over the floor?  That's called scattering "" scattering is what happens when something spreads in many different directions.  Light shoots through space in a straight line.  But when it hits most solid things, it bounces all over the place.  It scatters.  If light waves only reflected in a single direction, you would have to stand in one place in order for your eye to catch the waves.  If the waves did not happen to hit your eyes, you would not see it at all!  Since light scatters, you can see a table in front of you and so can another person on the other side of the room.

Light can bounce off all sorts of things.  Imagine looking at a light through a glass of water.  It's easy to see the light, right?  That's because light is moving in a pretty straight line through the water and glass.  It's like a car driving down the freeway with only a couple other cars.  But now try to look through a glass of milk.  Some light comes through, but it's hard to see through to the other side.  The freeway has a traffic jam!  The light is coming in through one side and bouncing off the milk or diffusing.  Diffusion is when light is scattered many times.  By the time light makes it through all the milk, it's a lot weaker because it's been scattered so many times.

Light waves cannot go through some things at all.  Put your eyes right up to the wall and see if you can see any light coming through from the other side.  No?  That's because the wall is opaque.  If something is opaque, it means that light cannot pass through it.  It blocks light waves like a tree fallen in the road blocks cars from driving.  Can you think of three things that are opaque?  If you can't think of any, pick up something around you, hold it up to your eyes, and see for yourself!

There are some kinds of matter light can pass through very easily.  I'll bet you can think of one right now.  We even talked about it in this article . . . Yes!  Glass.  Light can also pass through some kinds of plastic, like a water bottle.  Anything else?  How about water that doesn't have anything else in it and is very clear?  All of these things are transparent.  When matter is transparent, it means that light can pass through.  You don't even have to put your eyes right up to it.  Just look out the window.

Look around!  Like matter, light is all around us.  Light is bouncing around like a ball.  Light is scattering every which way.  Not only is studying light cool, it is great when you are afraid of the dark!