I totally understand the first answer to my question but how can i make it understandable to an eight year old. I think that he won't understand the concept of refraction. He does understand about feeling wind against the skin. I thought that maybe I could get him to see a rainbow when the lawn sprlinkler is on from one angle and then move to another angle from the sun to make it disappear. Do you have any other suggestions. Thank you.
Why not get him a simple prism from a novelty shop or even better, from a science shop. The one from the science shop is more likely to have instructions and explanations on light properties with it.
Let him play with a bicycle pump. He will soon understand that there's air in it which can be "pushed" against his face with a sharp push on the handle. Then put a finger over the outlet and get him to push the handle down and notice the difference - the air he now knows is in the body of the pump is resisting compression.
I'd steer clear of the refraction thing, honestly, until he's got a better grip on more basic stuff.
Air can never be seen. Things suspended in air and moving in its currents can be seen so maybe try showing him a smoky fire e.g. barbecue in the garden and explain how the heat causes the air / smoke to rise.