|MadSci Network: Physics|
Aaron, your question got a little complicated when I thought about it so I broke it into four questions: 1. Why can we feel the wind? 2 Why do we think that we cannot see the wind? 3. Why can we see things? and 4.When or how can we see the air or see the wind. Why can we feel the wind? Wind is air in motion. Air is made up of a mixture of very tiny particles called molecules. A cup of air contains about 6 billion trillion molecules[6.000,000,000,000,000,000,000], that's a lot more than the billions and billions served at MacDonalds. When the air, the wind, moves against us or we move thru the air, we feel these trillions of molecules hitting us from every direction. Since there are so many molecules the air feels smooth. As the wind becomes faster, it feels less smooth. When we feel the the wind the numbers of molecules that hit us each instant are changing or are different on different parts of our body. These changes are called pressure differences. We feel the pressure changes; we feel the wind. Why do we think that we cannot see the wind? This is because of two of the properties of air.[a property is something that describes or is part of something. properties that describe you: a boy, height, weight, hair color, etc.]. Air is almost completely "Transparent" to light. This means that light goes through it without being changed very much[we will see that it is changed a little bit]. Air is also "Homogeneous" [like homogenized milk]. This means that for short distances, say 100 meters to a mile, the air doesn't change very much. This means that when we look at it we see no changes and our brain simply dismisses it and says that we can't see it. If you are standing beside a swimming pool and look at the water you easily see the water, If you jump in, go under and open your eyes you don't see the water[if it is clean] any more because it is homogeneous[and transparent] and your brain dismisses it and gets busy looking for sharks. Why can we see things? We really can not see "things"! We see light. We see "things" because we either see the light they give off, things such as the sun , stars, light bulbs, lasers, LEDs, lightning bugs, TV screens, movie projectors. OR we see things because light [from one of the things that gives off light ] bounces off or is reflected from an object. Such objects are you, me, a movie screen, the moon, the planets, a book, LCDs, anything that doesn't give off light. When you "see" something think, "Am I seeing this thing because it is giving off light or because it is reflecting light?" If it is reflecting light, Think, "Where is the light that it is reflecting coming from?" An experiment to try to show that you really only see light can be done. You will need your Mom or Dad or both to help out. After dark go into a room in your house that has a large walk in closet with a door that can be securely closed. Open the closet door with the room lights on and look in , you will be able to see what is in the closet. Go into the closet with your Mom or Dad and stand looking out the door. Have the other person turn off all the room lights, but leave a light on in another room that you cannot see directly. At first you will not be able to see much. As your eyes adjust to the low light"adjust to the dark" you will start to see things but not very well. Turn around in the closet and have your Mom close the door. If the closet is truly light tight you now will not be able to see anything. As you wait your eyes will not "adjust to the dark" because there is no light for them to adjust to. Conclusion: We see light, not things. When or how can we see the air or the wind? We must look for the times and places where the air changes. The simplest place is to just look up into the clear blue sky. Remember, we see things because they either give off light or they reflect light. Well the atmosphere can give off light in lightning or in the northern lights or aurora borealis, but the sky is blue only in the daytime and only when the sky is clear. So the atmosphere must also be reflecting light from the sun, the correct term is that the light is "scattered" by the molecules in the air. Seeing the blue sky is seeing the air or wind. The clouds racing across the sky are moving with the wind so again we can see the wind. If one looks along a hot road, railroad track, or sidewalk and sees wavy lines in the air, one sees the hotter air moving upward, an updraft. The funnel cloud in a tornado would probably be visible even if it didn't have trees and rooftops spinning in it. Every chance you get, look around and see how many ways you can see the air , see the wind. Both Compton's and Encarta Encyclopedias have sections on wind, air and the molecules in air which are fair to good in content and accuracy. An 8th grade Earth Science text book from the school library would also be a good source of information.
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