That Sinking Feeling

Helium-filled balloons are lots of fun because the balloon lifts up into the air. But they don't last long. Within a day or two, they begin to sink lower and lower, and to get smaller and smaller. Why does this happen?

This is an example of a process known as effusion. Effusion occurs when gas molecules are able to escape their container through a little hole. All gas molecules, whether they're heliums in the balloon, or nitrogens, oxygens, or something else in the air, are moving around really fast (around 1000 miles per hour!!). Every now and then, one of them finds a hole and gets out. Understand that these are very, very tiny holes - too small for you to see. Helium atoms are much smaller than molecules like nitrogen, oxygen, or carbon dioxide, so it's a lot easier for them to get out the hole. They also move faster, so they find the holes more quickly.

You might try some experiments with effusion. Get two helium-filled balloons - one rubber and one Mylar (the shiny kind). Do they both lose helium at the same rate? Compare a helium-filled balloon to one inflated with air or your breath (which has more carbon dioxide than the air you breathed in). Can you see the difference in gas effusion?

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!

Fun Facts 4

Continuing with our cavalcade of fun facts:

• The skeletons of certain types of sponges and other sea creatures are made up of silicon (Si, #14) dioxide, or SiO2. SiO2 is also the main component of glass, sand, and many rocks.
• Adding molybdenum (Mo, #42) to steel makes the metal even stronger. "Moly steel" was developed in the early 1900's, but a Japanese sword made in 1330 contains a lot of molybdenum. No one know how this was done!
• Bohrium (Bh, #107) is named after the Danish physicist Niels Bohr, whose birthday is today, October 8! Tillykke med fødelsdagen, Niels! (Apologies to any Danish speakers out there if this isn't right). Bohr was the scientist who first thought of the "miniature solar system" picture of the atom. Scientists later realized that this picture wasn't exactly right, but it was still an important idea!
• Osmium (Os, #76) is the densest metal. A one-foot cube of osmium would weigh over 140 pounds - that's heavier than many adults!
• Gadolinium (Gd, #64) is one of the elements called "rare earths" (#57 - #70), but it really isn't terribly rare. In fact, there is more Gd on earth than tin!
• Europeans didn't "discover" the beautiful silvery metal platinum (Pt, #78) until the 1700's. However, the native people of the Americas knew about it long before that!
• If you've ever flown on a plane, you know that the flight attendants tell you about the oxygen (O, #8) masks that drop down from the ceiling in case of a problem. The plane doesn't actually have containers of this gas (that would be dangerous), but they do carry chemicals that make oxygen when they react. If there is a problem, the two chemicals are mixed very quickly, and you can have oxygen gas to breathe!
• People with high blood pressure sometimes use a salt substitute instead of regular salt. This fake salt is actually potassium (K, #19) chloride.
• The metal indium (In, #49) makes a crying sound when a piece of it is bent!
• Radioctive neptunium (Np, #93) is the heaviest element found on earth, but it's only here in very tiny, tiny amounts.