A Homemade Barometer

Using common, household materials, we can construct a simple barometer to measure changes in air pressure.

The $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

A classic investigation into the chemistry of bones.

The $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

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.

The $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

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.

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.

Yesterday's walk on the beaches of New Zealand gave me a great experiment. I was playing with the ironsand, a very heavy, black sand made of titanomagnetite. There is a large deposit of ironsand on the beach at the farm. In trying to sort the different minerals, I was reminded of my gold panning trip to the Carolinas back when I worked at the Memphis Pink Palace Museum, in Memphis, Tennessee. To try your hand at "gold panning," you will need:

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.

This project has science fair potential.

Link to Sunglass Science: Polarized Light

This time we will explore things that are usually invisible, revealing new things about the world around us.

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

Link to Whistle Stick, part 1

I hope that you made your own Whistle Stick, and have been playing...., I mean experimenting with it. I also hope that you spent some time thinking about the science behind the sound that it makes, because that is what we are going to explore this time. For your exploration, you will need:

- a wooden spoon
- a large container of water
- the Whistle Stick from last week

It's always good to start with the basics, so begin by thinking about sounds in general. We hear a sound because of waves traveling through the air. Just as dropping a stone into a pond causes waves to spread out across the water, popping a balloon, vibrating a guitar string, or singing a song causes waves to spread through the air. When those waves hit our ear drums, we hear the sound. That means that the Whistle Stick must be producing waves in the air. But how? That is where the wooden spoon comes in. We will use it in place of the popsicle stick, and look at waves in water instead of air. Hold the wooden spoon between your palms, with the end of the spoon in a container of water.
Slide your palms to twirl the spoon slowly in the water. As the spoon spins, it makes waves in the water. Try spinning it at different speeds, noticing how that changes the distance between the waves. What you should notice is that as the spoon twirls, it pushes on the water to send out a wave. As you spin the spoon faster and faster, it makes more waves, and those waves get closer and closer together.
Now lets think about sound waves. The picture at the right shows a graph of the sound produced by the whistle stick. Notice that at the start of the sound, it reaches far up graph. The higher up the graph it goes, the closer together the sound waves are, and the higher the pitch of the sound. If you click the picture, you can watch a short video, letting you hear the sound, seeing how the changing sound matches the graph.
It is much easier to see (and hear) if we slow things down. This graph shows the same sound, stretched out four times longer than the original. That lets us see the curve as the pitch falls. Again, you can click the picture to watch a short video. Because it plays the sound slower, it is easier to see (and hear) that the sound begins with a high pitch (waves very close together), and then the pitch falls as the waves get farther apart.

Now lets put that all together. Like the wooden spoon, the faster the popsicle stick spins, the closer together the waves will be, and the higher the pitch of its sound. When you first snap your fingers, the Whistle Stick spins very fast, making a high pitched sound. As it pushes against the air to produce those waves, it gives up some of its energy of motion. That causes it to spin slower, producing a lower pitched sound. Looking at the graph, we can see that the rate of spin slows very quickly at first, and then more gradually.

If you remember from last week, I also made a Whistle Stick from a tongue depressor that was much wider. it made a much lower pitched sound, that did not last nearly as long. Why? The wider blade had to push against more air, transferring the energy of motion much faster, causing the speed of its spinning to drop much faster.

If you want to do some experimenting, you might try cutting notches into the sides of the stick or doing other things to change its shape. Do you think that would change the sound? Sounds like a good reason to eat more popsicles to me.

Link to Sunglass Science: Birefringence Light

Grab your shades for a different way of seeing the world around you.

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

This week's experiment is a trick that my Grandfather taught me when I was very young. He called it a "whistle stick", and making one brought back delightful memories from my childhood. This experiment requires the use of a sharp knife, so if you are young, you may need adult assistance. It is not difficult, but even adults should keep safety in mind. To try this you will need:

- a popsicle stick (with the popsicle removed) - a sharp knife with a short blade - a pencil or pen Making a Whistle Stick requires some whittling, the art of using a knife to shave thin slivers from a piece of wood. During my Grandfather's time, whittling was a common pass time, sometimes for carving interesting things, and sometimes just to give your hands something to do while you were thinking. While there are specialized knives for wood carving, most sharp pocket knives can be used for whittling. A dull knife will not work well, making it much harder to shape the wood, and much more likely that you will cut your finger instead.
The first thing to do is to eat the popsicle so you can get at the stick. Of course you can buy popsicle sticks from a craft or hobby store, but what is the fun in that? Once all of the icy treat has been removed from the stick, we will use the pencil to mark the parts that we want to remove. Starting about an inch from one end, draw lines from each side that come inwards towards the end, as seen in the photograph.
Now comes the part where you have to be careful and patient. We are going to whittle away the wood that is outside those lines. Hold the piece of wood in your left hand (if you are right handed), and with the marked end pointing away from you. Holding the knife in your right hand, with the sharp edge pointing away from you as in the photo above. Always cut away from you, never towards your hand. You want to cut away very thin slivers of wood. Trying to cut too thick a slice will split the stick. Once you get the stick close to the right shape, start cutting even smaller slivers, shaping and rounding the end. Don't worry if you make a mistake along the way. You can always eat another popsicle to get another stick.
Your Whistle Stick is now complete. To use it, press your finger and thumb together, as if you were going to snap your fingers. You can use either your first finger or your middle finger. Place the whittled end of the Whistle Stick in between finger and thumb. Then snap your finger. The Whistle Stick should fly away, making a strange, whistling sound. You may have to practice a few times, and the video should help with how to hold it and what to expect. At the end of the video, I try the same thing with a tongue depressor which is quite a bit wider than the popsicle stick. Notice the difference in the sound.

Once you have played with the Whistle Stick a bit, then it is time to do some scientific thinking. Why does it make that sound? Why does the tongue depressor make a different sound? Listening to the two, you should be able to figure out what is happening. Give it some thought, and some experimentation (which may mean that you need more popsicle sticks), and we will look into that deeper next time.

Have a wonder-filled week!

Link to Whistle Stick, part 2

Link to Part 1

Link to Part 2

The answer to Part 2, and a fun "science trick."

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

This week's experiment comes from Sheldon Schafer, Director of Science Programs and Facilities at the Lakeview Museum of Arts & Sciences in Peoria, Illinois. (http://www.lakeview-museum.org) He told me that much of the USA would have a partial solar eclipse on Christmas Day and suggested this experiment as a safe and easy way to follow the eclipse. If you miss the eclipse or do not live in an area where it will be seen, there are other ways you can see how this works. I will need those, as the eclipse will not be visible from where I am. You will need:

- a solar eclipse
- a piece of aluminum foil
- a pen or pencil
- a colander or a piece of pegboard
- a smooth, flat piece of paper

When viewing an eclipse, DO NOT LOOK AT THE SUN! There is a reason for this. First, you should never look directly at the sun, as it can damage your retina. During an eclipse, the visible light is much less, but there are still plenty of harmful rays. Since the visible light is less, the pupil in your eye stays open wider, letting in more of the harmful rays, making eye damage much more likely. The same goes for filters. They may filter out the visible sunlight, giving the illusion that they are protecting your eyes, when in fact they may be letting most of the harmful, invisible rays enter the eye.

To do this safely, you want to look at an image of the sun, instead of the sun itself. We will use a pinhole, similar to the pinhole we have used in past experiments (camera obscura, paper glasses). Cut a piece of foil about 6 inches square. Use the point of the pen to make a small hole in the center of the foil. Hold this about a foot above your piece of paper, with the sun (or a lamp) shining through the hole onto the paper. This will form a circle of light on the paper. Now, you may be thinking that the round circle is due to the round hole we made. To investigate that, watch the circle of light. Hold your finger about a foot above the foil and move it around. Looking at the circle of light, you will see the image of your finger moving over it. That is similar to what will happen during the eclipse, with the moon taking the place of your finger.

To see this with many images, hold the colander about a foot above the paper, letting the sunlight shine through the holes. On the paper, you will see lots of tiny circles of light. Now you might think that the dots were round due to the round shape of the holes. Many colanders have square holes, but you still get round circles of light unless you hold the colander very close to paper. What you are seeing is an image of the sun (or the light bulb in the lamp). As we have seen in past experiments, a small hole can act as a lens, either letting you see more clearly, or focusing an image as with a camera obscura. We are doing the same thing with multiple holes to give multiple images. As the eclipse begins, you will notice something happening to the circles of light. You will see the shadow of the moon slowly eat away into the side of each circle.

I first saw this in a much more amazing way. I was walking in the woods during an eclipse. If you have walked in the woods, you will notice that the light shining through the leaves forms lots of small circles of light on the forest floor. The spaces between the leaves form the "pinholes". That day, the forest floor was covered with crescents of light, letting me safely follow the eclipse while continuing my hike.

Today I was playing with sound experiments, and had so much fun with this one that I thought I would share it.  It is based on the original phonographs, which used a very similar setup to play recordings of music or voices.  To try this, you will need:

• 2 needles or pins
• paper
• a piece of cardboard
• tape
• (optional)  an old phonograph record.  Use one you don't mind damaging.

IMPORTANT!  Using this with a phonograph recording could damage it.  Do not try this with a recording that is important, valuable, or that will get you in trouble if it is scratched or damaged.  Flea markets are a good place to pick up an old record to try this with.

The first thing we need to do is to make a paper cone.  Roll the paper into a funnel shape.  Shape it so that the small end is almost closed, and the large end is as large as possible.  Use a piece of tape to hold it in place.

Stick one needle through the small end of the cone, about 1/4 inch from the end.  This will be your phonograph.

Let's start with the needle that is not through the cone.  Hold it in your fingers, and scratch it lightly across a piece of cardboard.  Listen carefully to the sound that it makes.  

Try the same thing with your phonograph, holding it by the paper cone, and trying to use the same amount of force that you did with the first needle.  You should hear a much louder sound.

Why is it louder?  Remember that things produce a sound by causing the air to vibrate.  The more air you can vibrate, the more sound you will produce.  As you moved the first needle across the cardboard, the point would catch on a rough place, and then spring free as you moved your hand forward, catching again and again.  This caused the needle to vibrate.  The vibrating needle caused the air around it to vibrate, producing a small sound.

When you tried the same thing with your phonograph, the needle also caused the paper cone to vibrate.  The paper cone has a much larger surface, which lets it vibrate more air, producing a louder sound.

If you have an old phonograph recording that you are willing to sacrifice, try moving the needle along the grooves in the record.  DO NOT USE YOUR PARENT'S RECORDS WITHOUT ASKING! You should hear the recording play.  Can you move the needle at the right speed to hear it correctly?

The early phonographs did not use electricity.  Instead, they worked just as your cone does, with a needle vibrating as it moves across a surface that has bumps and grooves, and a large cone to amplify the sound.

If you want to experiment some, try using a piece of paper that is not rolled into a cone.  Stick the pin through one corner of the paper, and try scratching it across the cardboard.  Does it work?  Compare the sound that it makes to the cone.  Is one louder?  Is one more directional than the other?  You could also try using a sheet of aluminum foil, a paper towel, a sheet of cardboard, and other materials instead of the paper.  What properties (density, stiffness, flexibility, etc.) give you the best sound?  With the proper approach, this could be turned into a very nice science fair project.  Hmmm.  I wonder how well it would work with one of those yummy sugar cones used for ice cream?  Sounds like a good excuse for a trip to the grocery!

Have a wonder-filled week.