"Say cheese!"  Today we record every move we make.  Cell phones, music players and tiny computers make it easy to take a picture of your friend making a silly face or riding his bicycle.  They also allow you to share with family and friends.  But you would not be able to keep these magic moments without light.  Pictures use light to freeze time, so you can see them again and again.

Just one more step back, perfect!

Eric Skiff from New York City, CC BY-SA 2.0 , via Wikimedia Commons

Normally, you see things for just a second.  Imagine looking out the car window and seeing a cute puppy as you pass by.  Your eyes open and let in the light that bounces off the puppy, just like light bounces through an open window into a dark room.  This forms a picture of the puppy inside your eye.  Even though you only saw it for a second, some parts of how the puppy looked will stay in your mind.  You have formed an impression of that puppy.  An impression is an idea or sign leftover after something can no longer be seen.

If you want to remember the puppy for a long time, you have to make that impression last for longer than a second.  It would help to have a special small box that keeps out light most of the time.  This box has a small piece of glass, called a lens, that lets light shine into the box; this is just like how your eye works.  Inside the box, this light falls on film that soaks up the light to record the picture.  A camera is the name for this box, lens and film used to record the picture.  Today's cameras often use a plate, instead of film, to record the light as a pattern of electrical charges.

Maybe not as easy as today's cameras.

Juhanson, CC BY-SA 3.0 , via Wikimedia Commons

Many years ago, making a picture took many steps.  To take a picture of the puppy, you would push the button to open the window, allowing light to shine on the film for less than a second.  There, chemicals on the film react with the light.  The more light that shines on the film, the darker it becomes.  Once you remove the film, you fix the picture in a darkroom, so the picture does not become all black, and print it.  A still picture recorded by a camera is known as a photograph.

OK, in this one I want everybody to smile.

Whitehead, F., Public domain, via Wikimedia Commons

But what if you want to record a moving picture, like your friend riding his bicycle?  You could draw a series of pictures in your notebook of him on his bicycle, and then flip through them quickly.  This tricks your brain; instead of seeing each separate picture, it sees one picture that moves with each page turn.  Or, you could use a camera built to record moving pictures.  These take 30 or more pictures each second, and they record sound too. Hand-held cameras that record moving pictures and sound are called video cameras.

Today, it is easy to record still and moving pictures of your friends and family.  Cameras with plates that record pictures and sound as electronic charges are used most often.  You can send these files in an email, post them to websites or print them on your home printer, just like you would print your book report.  Still, none of this could happen without light.  Light bounces off your subject, allowing you to record pieces of time.