Goal!

So how do those scent molecules get through the air to your nose? They do this by a process called diffusion. The nitrogen, oxygen, carbon dioxide, and other molecules in the air are moving around very fast (about 1000 miles per hour, even faster than a jet airplane!) When a scent molecules gets into the air, the molecules in air begin to hit the scent molecules, kicking it around like a soccer ball. Sooner or later, they kick it into your nose! Now, your nose probably can't smell just one scent molecule, but there are gazillions of air soccer players kicking around billions of scent molecules, so eventually a lot of them get to your nose. Not surprisingly, the farther away your nose is, the longer it takes to smell something. Also, the colder it is, the slower all the molecules move. And the bigger the scent molecule, the longer it takes to smell (usually).

Here's a way you can observe diffusion in action. Line up about 5 or 6 family members or friends in a row, each about 2-3 feet apart. You can do this in a large room, down a hall, or outside. Have them all face away from you and close their eyes. Tell each person to raise a hand when he or she smells something. Open a bottle of something smelly, like mouthwash, perfume, or rubbing alcohol. Turn around and look for raised hands. You will probably see that the people closest to you raise their hands quickly, but that it takes longer for the people farther away. Some may never smell it at all (especially if you're outside on a windy day). Try the same experiment with different kinds of smells and with more people!