Careful observation is a very important part of science. Ornithologists learn to identify birds from a quick glimpse as they fly through the trees. Meteorologists learn to read the clouds in much the same way that most people read books. Geologists learn to look at a hillside covered with gravel, and spot the one piece that happens to be a fragment of dinosaur bone. Part of this is learning what to look for, but part is also training your eyes to really see all the details that are there. To give this a try yourself, you will need:

• several chocolate chip, oatmeal raisin, or other cookies. Homemade are tastier, but you can use store bought cookies too.
• paper to draw on
• pen, pencil, crayons, or something else to draw with.
• a ruler

Pick two cookies at random. Eat one. Place the other on the table in front of you. Look at the cookie. I mean, REALLY look at it. Imagine that you are going to have to look at a pile of similar cookies, and know this one well enough to pick it out of the pile.

Draw a picture of your cookie, being sure to note any identifying marks. Maybe one of the chocolate chips has a crack in it, or there may be two raisins at the edge that almost touch each other. Don't worry if your drawing is not perfect. You are recording your observations, so as long as it shows the things that make your cookie special, it is a wonderful drawing.

Measure your cookie, noting on your drawing any measurements that could help identify it. Maybe one side is thicker than the other, or it may be 1/4 inch wider at the point where the two raisins almost touch. Again, pretend that you need to record your cookie well enough to pick it out of a lineup of other cookies.

Once that is done, put your cookie in with all the others. Close your eyes and have someone mix them well. If you are doing this on your own, close your eyes and shuffle them well. Then open your eyes, and find your cookie. Check it against your drawing and measurements to be sure that it is your cookie.

How well did you do? If you want to make it a bit more challenging, try using cookies that are manufactured to be very similar. Oreos work very well for this. They all seem to look alike, but if you look carefully, you can spot irregularities in the filling, top cookies that are not exactly aligned with the bottom, and other small differences.

Want to make it a bit more challenging? Ask someone else to look at your drawing and notes, to see if they can identify your cookie. This takes more practice and skill, but it is a skill well worth learning.

Once you are done, you will have a pile of cookies that have been handled. That means that you can't put them back in the package, so dispose of them properly. I like mine dipped in either milk or hot tea.

The more you practice observation, the more you will see in the world around you. You can do this activity with other objects, such as pennies, rocks, leaves, or sticks, but in that case, skip the step where you eat one.

Printer Friendly File - Printable Graph Paper

With the holidays upon us, I am once again reading through Michael Faraday's Chemical History of a Candle. You can find it online at http://www.gutenberg.org/etext/14474. Truly a wonderful book. I was trying to think of a new candle experiment and came across a package of the "magic relighting candles" in the birthday card section at the grocery store. These are the ones that relight themselves a few seconds after you blow them out. How do they work? Let's find out. You will need:

• a candle
• a lighter
• one of the self relighting candles

First, lets burn the regular candle. Place it in a secure holder, so it does not fall over. Light the candle and let it burn for a couple of minutes. Check to see that it has formed a nice pool of melted wax around the base of the wick. Then blow out the candle. You should see a column of white smoke rising from the wick. Blow strongly on the wick, and you should see an ember glowing at the end of the wick. That ember and the white smoke are two of the important parts of the relighting candle.

The white smoke is really vaporized paraffin, the stuff the candle is made from. The glowing ember is hot enough to continue vaporizing the paraffin, but not hot enough to set the vapor on fire to relight the candle. That calls for a third ingredient.

Place the relighting candle in a holder. I have found that a cupcake or brownie works very well for this. I also put a little ice cream around it, just for safety. Light the "magic" candle, and let it burn for a few seconds. Then pretend it is your birthday, and blow out the candle. Watch the candle carefully. You should see the same rising column of white smoke. You will probably also see the glowing ember, but do not blow on the wick this time. Instead, watch closely. After a few seconds, the candle relights itself. Just as it relights, you should see something else. There should be tiny, bright sparks that jump from the wick. That is the third thing that we need to have a relighting candle, but what makes the sparks?

The sparks are caused by tiny bits of the metal magnesium. Magnesium is a very light metal. It also burns with a very hot flame. Tiny bits of magnesium are mixed into the wick. While the candle is burning, liquid wax flowing up through the wick keeps the magnesium cool enough not to burn, but once the candle is blown out, the wax cools and stops rising. That lets the glowing ember heat the magnesium bits enough to set some on fire. They burn hot enough to set the paraffin vapor on fire, relighting the candle.

If you relight the candle several times, you will probably get some nice bursts of sparks. Repeated melting can cause some of the particles to concentrate in one place. When they get hot enough, you get a nice, miniature fireworks display.

Once you are done, but sure that the "magic" candle is out. Put it in some water for a little while to be sure. It would not be a good thing to put it into the garbage, and then have it relight again.

Be sure to dispose of the cupcake or brownie properly too, preferably with a little hot fudge sauce and a fork.

To go into this subject deeper, try the following:

The Fire Diamond: To understand what we need to have a fire.

This activity is from my Experiment of the Week Newsletter. It is free, and will let you know about new resources on this site.

This time, we are going to take a look at a classic science experiment that has been used for a LONG time. In fact, it was already an old classic when I was a kid, and that was quite a while ago.

The experiment involves the link between our senses of taste and smell. Often it is done with apples and potatoes, but there is enough textural difference that you can often tell which is which. I have found that the results are much stronger with flavored candy. To try this, you will need:

• candy that has the same shape and texture, but comes in different flavors.

OK, lets begin with the standard experiment. Be sure that your pieces of candy will all feel the same in your mouth, and that they have distinctive flavors. If you don't see the candy, the taste should be your only clue to what flavor it is.

If you have a friend to help, then close your eyes, hold your nose, and have her give you one of the pieces of candy. Keeping eyes and nose tightly closed, put the candy in your mouth. You will taste a sweet taste, and probably some sour too, but you may be surprised that you can't tell if the candy is cherry, lime, orange, or some other flavor.

Then move your hand away from your nose, so you can breath normally. Yum! You get a sudden burst of flavor, telling you exactly what kind of candy it is. The reason for this is that your tongue has flavor receptors for basic flavors, such as sweet, salty, sour, bitter, and umami (the savory taste of meat.) Most of the other flavors that you taste are tied in with your sense of smell. If you can't smell them, then you don't taste them. That is why food tastes so bland when you have a cold.

But wait a minute! Your parents probably taught you to chew with your mouth closed. How can the smell get out of your mouth to go up your nose, so you can smell it? And your mouth stayed closed when you released your nose, but you still got that sudden burst of flavor. What is really happening?

Well, the smell of the food does have to reach your nose for you to taste all of those subtle flavors, but there is another path that those smells can take. Instead of inhaling those smells through your nose, you are exhaling them. As you breath out through your nose, your breath carries the smells from your mouth into your nose. You were not holding your nose to prevent you from inhaling the smells. Instead, you were blocking the way, so you could not exhale the smells through your nose.

Now that you are tasting the flavor, hold your nose again. After a second or two, the flavor disappears again.

So what if you just held your breath instead of holding your nose? Try that.

No, really. Try it and see for your self.

What did you find? Even holding your breath, you probably still tasted some of the flavor. Why? Think about what happens when you chew or swallow. Your mouth changes shape, your throat moves, your tongue moves around. All of that movement causes the air in your throat to move, forcing some of it up into your nose. It carries some of the smell to your nose even if you don't exhale. By blocking your nose, you pressurize it, preventing the air from your mouth from moving up.

OK, take it one more step. Hold your nose until the flavor goes away. Then release your nose, and inhale. While you are inhaling, keep your mouth closed. You probably won't taste the flavor. Then exhale. Ahh, there is the flavor again. The main path that the smells take to let you taste your food is up through the back of your throat. It is not inhaling that brings you the flavor. Exhaling is what gives you those wonderful flavors.

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I first became interested in rock stacking during our trip to Technorama, the Swiss Science Center. Thorsten Künnemann, their Executive Director took us on a marvelous tour of Zurich. As we walked along the shore of Lake Zurich, we came to an area that was filled with amazing stacks of balanced rocks. When you first see them, you think that they must be held together with glue or mud. Only when you get very close can you see that it is all a matter of balance. Since then, we have seen similar stacks in other places and made some of our own.

If you would like to try rock stacking, you will need:

• a flat, stable surface
• a variety of rocks or other things to stack
• steady hands
• lots of patience

While at first rock stacking may seem like a frivolous activity, there is actually quite a bit of science and engineering involved. As we saw in the Science of Balance video, we can balance an object by keeping its center of gravity (its balancing point) directly above its base (the part of the object that is supporting it.)

To start, you need a wide variety of rocks, or other objects to stack. If you don't have lots of large rocks, you might try stacking toys, stuffed animals, or other irregularly shaped objects that are not breakable.

Select a large, steady rock as your foundation. You want the rock on the bottom to be very stable, because if it wobbles, your entire stack will wobble, which usually means that it all falls down. By using a wide, flat rock, it has a large base, which gives you plenty of working room to keep the center of gravity inside that base. While you are learning the art of rock stacking, you will have better success if you also choose a foundation rock that has a fairly flat top, to make it easier to balance the next rock.

It is easiest if you start simply, using fairly flat rocks to make stacking easier. Keep in mind that as you add each rock, you are adding pressure to the rocks under it, which may shift their center of gravity. Work slowly. Instead of putting a stone in place and releasing it, gradually let its weight rest on the stack, checking to see whether the stack remains stable.

Once you have the knack of stacking flat rocks, then you can start to get more creative and adventurous. Use rocks with unusual shapes, and try balancing them on smaller bases. Remember that a smaller base means you have to be more careful with the stack's center of gravity. Also remember that each rock can change the center of gravity of the entire stack, throwing the stones below it out of balance. If one orientation is unstable, try turning the rock to a different side. If that does not work, then try a different stone. The more you practice; the more you will learn about the art and science of stacking rocks.

As we saw in the Scavengers and Decomposers video, mushrooms play a major role in the food web as decomposers, breaking down wood and other plant material, and putting some of that energy back into the food web. There are over 14,000 species of mushrooms, and many of them look very similar. We use many different characteristics to identify them, including their shape, their color, their texture, where they grow, and many other things. One important test that can help identify a mushroom is its spore print. Spore prints are easy to make, and some are quite beautiful.

To make a spore print, you will need:

• white paper
• black paper
• one or more mature mushrooms
• scissors or a knife
• clear, acrylic spray (optional)

First you will need some mushrooms. They need to be mature, which means that they have opened fully, often into the shape of an open umbrella. If you don't have any mushrooms growing around your house, you can usually buy them at your local grocery store. You don't want the small, white, button mushrooms. They are not mature yet. Instead, look for the pancake shaped Portabella mushrooms. That is what the button mushrooms would look like if they grew and matured.

Looking at the underside of the mushroom, you may see many thin ridges and grooves radiating from the center. These are the gills. No, they are not used for breathing like the gills of a fish, but they have a similar shape. The gills are where the spores are produced. OK, so what are spores? Spores do much the same job for mushrooms that seeds do for flowering plants. The difference is that mushroom spores are very tiny (You usually need a microscope to see an individual spore.), they don't contain the stored food that seeds have, and they don't have to be pollinated. Each tiny spore is capable of growing into a new mushroom. Not all mushrooms have gills. Some have pores or other openings, but they can still produce spore prints.

If possible, collect two specimens of each type of mushroom. Why? Some mushrooms have white spores, while others have dark colored spores, so for each kind of mushroom, we will put one on white paper and the other on black paper. If the mushroom has white spores, they will be hard to see on the white paper, but will stand out on the black paper. If the spores are dark, then the white paper will make them easy to see.

You want the mushroom to lie flat on the paper, so use scissors or a sharp knife to remove the stem. As you do that, watch closely. Many mushrooms will change color when they are cut or broken. This mushroom was white when it was first cut, but within seconds the cut changed to a dark, rusty red. That color change is another useful trait that can help you identify mushrooms. Not all mushrooms have dramatic color changes, so if you are using a Portabella, you will probably not see much at first, but it will slowly darken.

Place the mushrooms with the gill side down on the sheets of paper. Put them in a place where they will not be disturbed, and let them sit overnight. The spores are so small that even a gentle breeze can carry them away, so if you have a fan or air vent nearby, you should cover the mushrooms with a bowl or a box. As the mushroom sits there, it releases spores, which fall onto the paper.

By the following morning, you will probably be able to see a dusting of spores on the paper at the edge of the mushroom. Very carefully, lift the mushroom off of the paper, being sure not to let it shift or slide. Underneath, you should find a spore print in the shape of the mushroom, usually showing the pattern of the gills.

Different mushrooms form different colored spores. This one had spores that were a very nice green color. You can preserve your spore print by very gently spraying it with a clear, acrylic spray. This spray is often used to protect art projects. Don't hold the spray can too close, as that will blow away many of the spores, and form drips that will mess up your spore print.

On the sheet of paper, write the date and location where the mushroom was collected. You might want to attach a photograph or drawing, and any other information about color changes when cut, texture, shape, etc. If you are able to identify your mushroom, then write its common name and its scientific name on the paper too. You may want to start a collection of mushroom spore prints, and might even decide to become a Mycologist, a scientist who studies mushrooms and other fungi.

Several people have written me lately, asking how to make simulated geodes in egg shells. Geodes are pockets of crystals that form in sedimentary and igneous rocks. They start as hollow spaces in rock that is porous enough for water to seep through. The water carries dissolved minerals, which are deposited in the open space, forming a lining of crystals. Most geodes contain quartz crystals, but they can also contain calcite, celestite, and other minerals.

Many rock shops and museum gift shops sell geodes that have been cut, and sometimes dyed to make them more colorful. Sometimes you can buy unbroken geodes, which lets you break them open yourself. That is particularly fun, as you never know how it will look until you open it.

If you don't have a place to collect geodes, you can make quick, easy, simulated geodes by using egg shells for the hollow spaces. I have seen several different recipes, many of which take days, but you can make an egg shell geode in a few hours by using epsom salts for the crystals. We will be using basically the same formula that we used for Growing Crystals from Solution, so you will need:

• several egg shells, washed and cleaned
• an egg carton to hold the shells
• epsom salts, available at pharmacies and grocery stores
• hot water
• a measuring cup
• a refrigerator
• food coloring

Start by making an omelet or something else yummy that requires eggs. For the best results, crack the eggs close to the small end of the egg. This leaves you a fairly large egg shell to use. The larger the egg shell, the more crystals you will have. Wash the shell, and remove the skin-like membrane that lines the shell. For short term projects, you can leave this membrane in place, but you should remove it if you plan to keep your geode for a long time, as the membrane tends to mold after a while.

Depending on how many eggs you are going to use, you may not need as much of the solution as we used before. I tried using 1/4 cup of epson salts and 1/4 cup of hot water, and it worked fairly well for 6 egg shells. You want the water to be hot, but not boiling. Stir in the epsom salts. If it all dissolves, add another spoon full. Place the egg shells in the egg carton, so they won't tip over and make a mess. Then pour the epson salt solution into the shells.

If you want brightly colored crystals, add a drop of food coloring. You might even try adding small drops of two or more colors to the same shell. Be sure to leave some of them uncolored, because I think the pure crystals are prettier than the colored ones.

Carefully place the egg carton into the refrigerator. Put it in a place where it will not be bumped or disturbed, and let it sit for at least 3 hours. That will give your crystals plenty of time to form.

Once you have plenty of crystals, remove the egg carton from the refrigerator. There will still be liquid in the shells, which you can carefully pour into the sink. Be careful not to let the crystals fall out of the shell as you drain them. Each shell should have a mass of needle-shaped crystals inside. As they dry, they will become even more bright and shiny.

You can play with the concentration of the epson salts. Adding more epson salts to the water will give you a denser cluster of crystals, while adding a bit less will give you a better view of the individual crystals. If you used clean egg shells, your crystals should remain bright and shiny for weeks.

This is something that comes up quite frequently in discussions between scientists and the general public. How much proof does it take for a theory to graduate to being a law?

Theory

Law

Because the words theory and law have such different meanings in the language of science, it is often a difficult question to answer, so instead, I'll start by giving you a few similar questions to answer.

1. How perfectly do you have to build a house so that it will become a single brick?
2. How well do you have to write to change an entire dictionary into a single word?
3. What would you have to do to change an entire symphony into a single note?

If you are thinking that those questions don't make much sense, then you are feeling very much like a scientist who has been asked "How much proof does it take for a theory to graduate to being a law?" A house is made up of many bricks, boards, nails, windows, doors, concrete, etc. A dictionary is made up of thousands of different words, and a symphony can easily have thousands of notes that all fit together in just the right way to produce pleasing music. In the same way, theories are based on a variety of scientific laws, facts, testing, and other evidence, all fit together in a way that offers an explanation of how some part of the universe works.

Ohm's Law

In science, laws are simple facts and formulas that are so basic that they apply universally. For example, Ohm's Law has the formula I=V/R, which tells us that in an electrical circuit, the amperage is equal to the voltage divided by the resistance. That is it. All of it. It is an important law if you are working with electricity because it applies to any electrical circuit, but it tells us nothing about what amperage is, why it equals voltage divided by resistance, or what we can do with the information. It is simply one of the "notes" in the symphony of Electromagnetic Theory, which explains why light bulbs light, why electric heaters heat, and why computers compute.

So just as houses don't become bricks, theories don't become laws. Both are important, but they tell us very different things.

But what if a theory turns out to be wrong? What if it has a flaw? Well, lets go back to the earlier questions. What if you build a house, and then realize that there is a room with no door, no way to get in or out. Clearly, something is wrong. Do you walk away, and start all over from scratch? Or do you look to see if there is a way to install a door to make the room useable? Or maybe you decide that the room is not necessary, and remove that part of the building. The same is true for scientific theories. Finding one flaw in the theory of gravity would probably not send everyone back to construct an entirely new theory. Instead, scientists would examine the new evidence, and see if there was a way to adjust the theory so that the new evidence fit. That happens quite frequently. As we learn more and more about the universe, we expand and refine our theories about how the universe works.

Occasionally discoveries are made that are so profound that they do require that we discard the old theory, and start from scratch to develop a new one that fits the new evidence as well as the old. Then the testing begins, with everyone looking for evidence that the new theory is wrong. Wrong? Isn't it mean to try and prove that it is wrong? No. It is the way of science. In the words of a famous scientist:

Even after all those years, scientists are still performing tests to see if there are flaws in Einstein's Theories of General and Special Relativity. Neither has been shown to be wrong, so they are still accepted and highly respected scientific theories.

The same is true for new explanations of how and why things work. After a great deal of testing, and with enough solid evidence, often with much modification as more evidence is gathered, a new explanation may eventually be accepted for the exalted title of Theory.

Why do we have to study science? What good is it? For that matter, what is it? That question, "What is science?", is a very good one, and not easy to answer. Many different definitions have been proposed by different sources. After looking through many of them, I have tried to combine and distill them into a workable definition that we can use in our study of science.

OK, so for our purposes:

As we have seen before, the easiest way to understand long definitions is to take them apart, and look at them bit by bit. Then, when we put them back together, they are easy to understand. We can look at those parts in any order, but there are some parts that make it easier to understand others, so we won't just go down the line. Instead, I suggest that you look at them in this order.

1. The Natural World
2. Observation
• Answers to Observation video
• Observations on a Cookie.
3. Objective
4. Experiment
5. Repetition and Replication
6. Gather and Organize
7. Self Correcting

One of the main things that we use for identifying clastic sedimentary rocks is grain size, the size of the pieces. Rocks that have been deposited by water or wind tend to be very well sorted, with all of the pieces being pretty much the same size. How does that happen?

To find out, you will need:

• a glass jar with a lid
• water
• gravel
• sand
• clay or fine dirt

I used gravel from an old aquarium, but you could also use pebbles from a stream or even gravel from the side of a road. My sand came from the beach, but you can also find sand at garden supply stores, in playground sandboxes, and in streams. My clay came from our garden, but you can use dirt from your yard or potting soil.

Start by filling the jar about half full of water. Add a couple of hands full of sand. Then add some of the clay or dirt, followed by a layer of gravel. You can add some more sand and some more clay if you want. The more you mix the different sized sediments, the better. By the time you finish adding sediment, the jar should be nearly full.

Put the top on the jar, and give it a good shake. Remember that there is gravel in the jar, so don't shake it hard enough to break the glass. You want to be sure that the sediment and water are well mixed. Then swirl the jar for a moment to get the water moving round and round inside the jar. Place the jar on a table, and observe it carefully for the next few minutes.

You should notice that the gravel settles to the bottom almost instantly. Why? The pieces are heavier. The moving water pushes on all of the particles. If the water is moving fast enough, the particles will keep moving. As the water slows down, the heavier particles fall to the bottom. As the water continues to slow down, the sand will settle out next, followed by the clay. You will probably find that the smallest particles of clay will stay suspended in the water for a day or more before they settle to the bottom.

Now lets apply what we have seen to the real world. Imagine a beautiful, mountain stream. The water is flowing quickly, splashing and swirling along. What would the bottom of that stream look like? Do you think it would have a mud bottom? No. The water is moving too fast to deposit mud, or even sand. The bottom of that mountain stream would be mostly rocks. All of the smaller sediments would be carried on down stream.

If we follow that stream down out of the mountains, we will find that as the slope decreases, it slows down. Now we start to see sand, mud, and gravel, but they are not all mixed together. In places where the water flows quickly, the bottom will be mostly rock and gravel. In places where the water slows a bit, you will find sand deposits, and in places where the water moves very slowly, you will get deposits of silt and mud. Fine clay is usually deposited in places where the water is sitting still, such as lakes and swamps.

Looking at the beach, we see something similar. Beaches that are pounded by waves tend to be mostly rock. The rushing waves carry away the smaller bits. As the waves rush up onto the shore, they slow down, dropping sand or small gravel, depending on their speed. Off shore, where the water is not moving as much, fine sediments settle to the bottom to form the silty mud that the divers on nature shows always seem to stir up at some point.

You can apply the same information to help figure out the ancient environments that deposited sedimentary rocks. Deposits of sand can become sandstone. Deposits of clay and silt can become shale. This tells you something about the water speed when they formed.

It may be surprising that the first thing that most people notice about a mineral, its color, is usually not very reliable for identifying it. That is because many minerals occur in a wide range of colors, colored by slight impurities. We can explore that by using a few things from your kitchen.

You will need:

• several clear drinking glasses
• food coloring
• water
• a spoon for stirring

Fill one glass about half-full of water. Place it on the table and look at it. What color is it? Clear, right? No surprise there. But, what if we added something to the water? Not something that would react with it chemically, to change it into something else. We just want something to change its color.

Adding coloring does not change the chemistry of water. No matter what color, it is still water.

Fill another glass about half-full of water, and place it on the table beside the first. Add a drop of food coloring to the water and give the water a quick stir. Compare it with the original glass of water. It’s a different color, but is it still water? Yes. Adding a tiny amount of coloring did not change its chemical formula. It is still water. Using different colorings, you can have water that is white, purple, black, pink, or any other color. As long as you don't change the water chemically, it is still water, no matter what color it is.

The same is true for the mineral quartz. It occurs in many colors, but they are all quartz.

Now, lets think about minerals in the same way. One of the most common minerals is quartz. Pure quartz is clear, just like pure water. Tiny amounts of impurities can color the quartz just as the food coloring colored the water. In the photo above, the crystal on the left is a pure, clear quartz crystal. But, what if that crystal was colored by impurities?

• Tiny bubbles of gas or liquid inside the mineral can produce white quartz, also known as milky quartz.
• Iron can color the quartz purple. Then, we would call it amethyst.
• Exposure to radiation can free some atoms of silicon from the quartz, coloring it grey or black. In that form, it is known as smoky quartz. This can be because of exposure to natural radiation, but some people change clear quartz crystals to smoky quartz by exposing them to radiation.
• Titanium, iron, or manganese can color quartz pink, which is commonly known as rose quartz.

All these varieties are still quartz. They all have the same chemical formula, the same hardness, the same fracture, the same crystal structure. They are different varieties of the same mineral.

With that said, there are times when color is useful in narrowing down the possibilities. While there are several minerals that can be purple, there are quite a few minerals that have never been found with a purple color. A bright purple specimen might be quartz, fluorite, or one of several other minerals, but it is probably not orthoclase or biotite. They just don't occur in a purple color. In cases where color may help, it will be noted on the identification chart under "other properties."

At some time in your life, you have probably heard that in a fall, cats always land on their feet. Is that true? Well, usually it is. Cats have the amazing ability to turn themselves right side up as they are falling. That does not mean that a fall will not injure them. If you fell off a tall building, would landing on your feet keep you from being injured? No. The same is true for cats. Landing on their feet lets their legs flex to absorb some of the impact, and keeps the impact from directly hitting more delicate bones, but cats do not have any magical protection against injury from falling.

What is amazing is the way that they perform this trick of landing on their feet. They do it by combining fast reflexes with the laws of physics. To get an idea of how they do it, you will need:

• a chair that swivels easily. Common office chairs work very well for this.
• an open area with plenty of room, so you don't break any lamps, furniture, or legs.

OK, lets start by thinking about what the cat has to accomplish. It is falling, which means that it does not have anything to push or pull on to turn itself. Instead of falling, you can get an idea of the problem that they face by sitting in the swivel chair. Make sure that you have plenty of open space around you by holding your feet straight out and turning in a complete circle. You want at least a foot or two of open space between your feet and the closest thing you could bump into.

Now lets get an idea of the challenge the cat faces. Sit cross legged in the chair, so your feet do not stick out. Put your arms in your lap, with your elbows tucked in against your side. Your challenge is to turn the chair around so that you are facing the opposite direction by twisting your body from side to side. Don't move your arms or legs. You can twist at the waist and your neck, but nothing else. DON'T HURT YOURSELF! You will find that you can turn the chair slightly to the right by twisting your body to the left. The problem is that when you twist back to the right, the chair spins back to the left, winding up back where it started. Wiggling the chair back and forth is no problem, but you don't get very far towards turning the chair around.

To see how the cat manages its trick, lets try something different. Keep your elbows at your side, but extend your hands out to the side. Then try twisting again. This time you will notice that the same motions cause you to swivel back and forth farther. Extend your arms all the way out, and try it again. Now, you are really moving back and forth. As you move your arms further and farther from your body, you can use their inertia (resistance to changes in motion) to push against.

You still have the problem that you are twisting back and forth. Remember that you are a falling cat, and you need to turn yourself so you can land on your feet. That leads us to your next step.

Extend your arms all the way out, and then twist to your left. That swivels the chair and your body to the right. Now, before you twist the other direction, pull your arms back in close to your body. Since your arms are in close, you can turn back without swiveling the chair back in the other direction. You have turned part of the way around, and you are back into the position to do it again. Extend your arms again, and repeat the process. It took me three arm swings to turn my chair around so that I was facing in the opposite direction.

Cats do this maneuver even better because they are incredibly flexible. They extend their front legs while pulling in their back legs, and then twist in the direction they want to turn. Very quickly, they pull in their front legs, and extend their back legs, making another quick twist that lets them wind up facing as much as 180° from their original direction.

Although cats are incredibly fast at this, it still takes time. Cats that fall from a very short distance do not have enough time to twist around. Also remember that landing on their feet does not mean that they don't get hurt during a fall. Their reflexes and flexibility can help them land in the best position, but they can still suffer injuries and broken bones from a fall; so you should not use your cat as an experimental subject.

If you want to experiment further, try holding a weight in each hand as you do the experiment. Do you think that will make it work better or worse? Try experimenting with different arm motions. I had interesting results from making the same motions that you would use for paddling a canoe.

Link to Penny Chemistry, part 1

Last time, we used a mixture of salt and vinegar to remove the tarnish from pennies. This time, we will get back some of the dissolved copper by collecting it on some iron nails. To try this you will need:

• a small glass, cup, or bowl
• vinegar
• salt
• several pennies
• several iron nails

The start of this experiment is pretty much a repeat of part of last week's experiment. Put a couple of inches of vinegar into a cup. Add a teaspoon of salt, and give it a stir to help it dissolve. This time, instead of dipping a penny halfway into the solution, drop in several pennies.

Very quickly, you will see the same thing happen that we saw last time. The pennies will lose their coating of oxides, becoming bright and shiny. In the process, some of the copper is being dissolved in the vinegar/salt solution.

To get some of that copper back, drop a couple of iron nails into the solution. After a minute or so, you will see tiny bubbles forming on the nails. After an hour or so, look at the nails again. They should have a thin coating of copper.

Why does the copper coat the nails? The solution that dissolved the copper from the pennies is also dissolving some of the iron from the nails. As the atoms of iron dissolve, they leave behind electrons, giving the nail a negative electric charge. Both the iron and copper atoms dissolved in the solution have a positive charge, but the copper is more strongly attracted to the nail, so the copper atoms stick to it, forming a coating.

The bubbles are hydrogen gas, produced by a reaction between the hydrogen ions from the vinegar and the metals. Once enough copper atoms have been deposited to balance out the negative charge on the nail, the process stops.

Does it make a difference if the nail is touching the penny? Try suspending the nail by a string, so it does not touch the copper. Does it still work? To see a stronger contrast, try suspending the nail so that only half is in the vinegar. That part should get a copper coating, while the part above the liquid should remain as it is.

Way back in the 70's, when I was working at the Memphis Pink Palace Museum, part of our Kitchen Chemistry program involved using packets of ketchup to remove the tarnish from pennies. You take a dull, brown, tarnished penny and rub it with some ketchup. In seconds, the penny is bright and shiny. Usually, the experiment stops there, but I thought we might take a look to see why it works. To try this, you will need:

• ketchup
• water
• vinegar
• salt
• potassium chloride (salt substitute)
• 5 small cups or bowls
• 6 or more tarnished pennies
• labels and a marker

Safety Warning

Before you go wild with pouring different chemicals together, remember to keep safety in mind. For the stuff in your refrigerator and spice cabinet, you can pretty much mix whatever you want. Tuna fish and grape jelly may not be tasty, but it will not explode or burn off your fingers. Outside your refrigerator, you need to be much more careful. Cleaning supplies and other household chemicals can be harmful by themselves, and if the wrong ones are mixed they can be deadly. Only use them for experiments that specifically call for them.

Experiment

A good place to start is with the original experiment. Put a little ketchup onto one of the tarnished pennies. Let is sit there for about 30 seconds, and then rinse it. What you should find is that the tarnish has been removed from the part of the penny that was in the ketchup. OK, so that works just as well as it did back in the 70's.

Next, take a look at the ingredients for the ketchup. Besides tomatoes, you will notice that two prominent chemicals are vinegar and salt. A little internet research will show you many other science experiments that use vinegar and salt for doing the same thing as the ketchup. If you want to be sure that the tomatoes are not responsible for cleaning the pennies, try using some tomato sauce that does not contain vinegar or salt.

After some experimentation, you will probably find that the vinegar and salt are the important ingredients but are they both necessary? Lets find out. Start with four small cups. Put about an inch of water in one. That will be our control. The control does not contain any of the chemicals that we are testing. If it cleans the pennies too that would tell us that the reaction happens, even without the vinegar or salt. Label this cup "Control."

In the second cup, put about an inch of vinegar. Label this one "Vinegar."

In the third cup, put about an inch of water, and then add a teaspoon of salt. Give it a quick stir to dissolve the salt. Label this one "Salt Water."

In the fourth cup, put about an inch of vinegar, and add a teaspoon of salt. Give it a quick stir to dissolve the salt. Label this cup "Vinegar and Salt."

Now, you are ready to do some testing. Lets start with the Control. Dip one of the tarnished pennies halfway into the water, and hold it there for 30 seconds. Remove it from the water, rinse it, and put it beside the Control cup.

Do the same for each of the other cups. Be sure to give each 30 seconds, and be sure to rinse the penny to remove any vinegar or salt. Place each penny beside the solution you used to test it.

Results

OK, now what did you find? If your results were like mine, you found that neither the water, the vinegar, or the salt water did much, if anything to the pennies. The mixture of salt and vinegar was very effective at removing the tarnish.

So what is happening? The tarnish on the penny is copper oxide, and a chemical reaction with the vinegar will actually dissolve it. Then why did the pure vinegar not work? With the penny and the vinegar, you get a series of chemical reactions that form a circle. One reaction removes the copper, but just as quickly, another reaction puts it back. In chemistry, this is known as an equilibrium reaction.

The trick is to add something that will interrupt that equilibrium. You want a chemical that will grab the copper before it can be put back, and the table salt does a very good job of that.

What is it about the table salt that grabs the copper? Table salt is sodium chloride. When you put it in water, it separates into sodium ions (charged atoms) and chlorine ions, but is it the sodium or the chlorine that grabs the copper. An easy way to test that is with a different kind of salt. One of the common salt substitutes is potassium chloride. You can find it beside the regular (sodium chloride) salt at the grocery. In a fifth cup, put about an inch of vinegar and stir in a teaspoon of potassium chloride. Does it work the same as the table salt? If so, then it is the chlorine that grabs the copper. If not, then it is either the sodium, or the combination of sodium and chlorine.

You can look deeper into the vinegar as well. Will it work with other acids? Try using lemon juice (citric acid and ascorbic acid) or carbonated drinks (carbonic acid). Carbonated colas also contain phosphoric acid. Again, remember safety. Look for acids from your refrigerator and spice cabinet, not from other household chemicals.

Link to Penny Chemistry, part 2