what you'll need
Also be sure to ask your mom, dad or another adult to help- they'll want to watch anyway when you tell them how cool this experiment is!
experimental procedure
observations
Does the candy glow in the dark before you crush it? Did you observe a flash of light as you crunched the candy with your pliers? It's not very bright, and it happens very quickly, but you should see a cool flash of light, like a spark. If it doesn't work at first, try again, and make sure the room is dark and your eyes are adjusted. What color is the light? Does it last very long? Does the candy get hot? Cold? If you have different types of candy or some sugar cubes, do you observe any differences in the light from each? If you have a sugar-free mint, does it make a flash of light too? If you have any other candies, try those and make observations.
what's happening
This is not a magic trick or an optical illusion- you really did produce light from an ordinary piece of candy!. This is a demonstration of tribo-luminescence, which means to make light by rubbing, scratching or crushing something, which is very different from most of the ways you are familiar with to make light. Nothing is burning, glowing or getting hot like the filament in a light bulb (although there may be a little heat from the friction as the candy is crushed). It's also not a chemical reaction like the light-sticks you may have played with before. And though it does look sort of like the sparks you see when some metals (like iron) are scratched or scraped by very hard materials (like flint), those are actually produced by spontaneous combustion (burning) of the metal as freshly cut surfaces of very small pieces react with oxygen from the air.
Triboluminescence is not very well understood by scientists, but most think it is similar to the lightning you see during storms or during one of our cool electricity demonstrations, which is actually a type of plasma discharge. Many materials, like the sugar in this experiment, have a very special crystalline structure that causes electrons to be ripped away from the nucleus of their atoms. Since electrons have a negative electrical charge and the protons in the nucleus have a positive charge, separating these charges can create an electrical field strong enough to rip electrons off gas molecules in the air, a process called ionization, and creates a localized plasma. These plasma ions can then slam into other molecules and transfer energy which causes them to emit photons of light. Those are the flashes you observed. Most of the light energy is emitted in the ultraviolet (UV) part of the electromagnetic spectrum, which is just outside the range of light that is visible to humans, but fortunately there is a bit of violet and blue light that we can see. You should have noticed that the flash of light from the Wint-O-Green Life Saver was significantly brighter, and may have also seemed to last a little longer. This is because wintergreen, the flavoring used in these mints, is a natural fluorescent dye called methyl salicylate. Fluorescent molecules can absorb energy of short wavelengths and emit their own light at a longer wavelength. In our experiment the wintergreen in the mint absorbs a lot of UV energy that we can't see, and emits greenish-blue light which we can see, so it appears much brighter to us.
variations and related activities
Try this experiment with ordinary table sugar (which you will have plenty of after you crush all your sugar cubes). Put a few teaspoons into a clear glass cup or dish (a Pyrex measuring cup works great) and slowly grind the sugar with a metal spoon to observe flashes of blue light. Try powdered sugar. You can also do the experiment in your mouth (bite very carefully so you don't break a tooth!) Be sure to look in a mirror so you can see the cool flashes of light in your mouth.
Here's another way to demonstrate triboluminescence: place a piece of Scotch tape onto a glass mirror or plate, then quickly rip it off in the dark. If you're lucky you should see a flash of light, but in our experience this experiment can be very finicky! Others have done this with Duct tape too. As was mentioned earlier, triboluminescence is not fully understood. Maybe you will be the scientist to finally explain this phenomenon! Most scientists believe air molecules play a role and that light should not be produced if the sugar is wet or under water, but we have observed flashes of light in both cases. What about other liquids? Humidity in the air can also affect the results (this is especially true for the scotch tape experiment). Let us know what you observe in your experiments in the Comments blog below.
references and links to more information
Some photos and videos of triboluminescence light flashes:
Others instructions for this experiment: Youtube video showing flashes of light from Duct tape: X-rays from Scotch tape:
Wikipedia article on triboluminescence: Journal paper from Towson State University researchers (yes, real scientists study this!):
Luz de Dulce - Triboluminiscencia (en español)
Admítelo, te encanta comer dulces. Pero, ¿sería aún mejor si sus dulces pudieran producir sus propios destellos de relámpagos? En este experimento, le mostraremos cómo hacerlo.
Lo que necesitarás
Procedimiento experimental
Observacione
¿El caramelo brilla en la oscuridad antes de aplastarlo? ¿Observó un destello de luz mientras machacaba el caramelo con sus pinzas? No es muy brillante y sucede muy rápido, pero debería ver un destello de luz fría, como una chispa. Si no funciona al principio, inténtelo de nuevo y asegúrese de que la habitación esté oscura y sus ojos estén bien adaptados. ¿De qué color es la luz? ¿Dura mucho? ¿Se calientan los dulces? ¿Frío? Si tienes diferentes tipos de dulces o algunos terrones de azúcar, ¿observas alguna diferencia en la luz de cada uno? Si tienes una menta sin azúcar, ¿también produce un destello de luz? Si tiene otros dulces, pruébelos y haga observaciones.
Qué está pasando
Esto no es un truco de magia o una ilusión óptica, ¡realmente produciste luz a partir de un dulce ordinario! Esta es una demostración de triboluminiscencia, que significa hacer luz frotando, raspando o aplastando algo, que es muy diferente de la mayoría de las formas con las que está familiarizado para hacer luz. Nada se quema, brilla o se calienta como el filamento de una bombilla (aunque puede haber un poco de calor debido a la fricción cuando se tritura el caramelo). Tampoco es una reacción química como las barras de luz con las que quizás hayas jugado antes. Y aunque se parece a las chispas que se ven cuando algunos metales (como el hierro) son rayados o raspados por materiales muy duros (como el pedernal), en realidad se producen por combustión espontánea (quema) del metal como superficies recién cortadas de las piezas muy pequeñas reaccionan con el oxígeno del aire.
Los científicos no comprenden muy bien la triboluminiscencia, pero la mayoría piensa que es similar al rayo que se ve durante las tormentas o durante una de nuestras demostraciones de electricidad fría, que en realidad es un tipo de descarga de plasma. Muchos materiales, como el azúcar de este experimento, tienen una estructura cristalina muy especial que hace que los electrones se desprendan del núcleo de sus átomos. Dado que los electrones tienen una carga eléctrica negativa y los protones en el núcleo tienen una carga positiva, la separación de estas cargas puede crear un campo eléctrico lo suficientemente fuerte como para arrancar electrones de las moléculas de gas en el aire, un proceso llamado ionización, y crea un plasma localizado. Estos iones de plasma pueden chocar contra otras moléculas y transferir energía, lo que hace que emitan fotones de luz. Esos son los destellos que observaste. La mayor parte de la energía luminosa se emite en la parte ultravioleta (UV) del espectro electromagnético, que está justo fuera del rango de luz que es visible para los humanos, pero afortunadamente hay un poco de luz violeta y azul que podemos ver. Debería haber notado que el destello de luz del Wint-O-Green Life Saver fue significativamente más brillante, y también pudo haber parecido durar un poco más. Esto se debe a que la gaulteria, el aromatizante utilizado en estas mentas, es un tinte fluorescente natural llamado salicilato de metilo. Las moléculas fluorescentes pueden absorber energía de longitudes de onda cortas y emitir su propia luz en una longitud de onda más larga. En nuestro experimento, la gaulteria de la menta absorbe mucha energía ultravioleta que no podemos ver y emite una luz azul verdosa que podemos ver, por lo que nos parece mucho más brillante.
Variaciones y actividades relacionadas
Pruebe este experimento con azúcar de mesa común (que tendrá en abundancia después de triturar todos los terrones de azúcar). Pon unas cuantas cucharaditas en una taza o plato de vidrio transparente (una taza medidora Pyrex funciona muy bien) y muele lentamente el azúcar con una cuchara de metal para observar los destellos de luz azul. Prueba el azúcar en polvo. También puedes hacer el experimento en tu boca (¡muerde con mucho cuidado para no romperte un diente!) Asegúrate de mirarte en un espejo para que puedas ver los fríos destellos de luz en tu boca.
Aquí hay otra forma de demostrar la triboluminiscencia: coloque un trozo de cinta adhesiva en un espejo de vidrio o un plato, luego rómpelo rápidamente en la oscuridad. Si tiene suerte, debería ver un destello de luz, pero en nuestra experiencia, ¡este experimento puede ser muy delicado! Otros también han hecho esto con cinta adhesiva. Como se mencionó anteriormente, la triboluminiscencia no se comprende completamente. ¡Quizás seas el científico que finalmente explique este fenómeno! La mayoría de los científicos creen que las moléculas de aire juegan un papel importante y que la luz no debería producirse si el azúcar está húmedo o bajo el agua, pero hemos observado destellos de luz en ambos casos. ¿Qué pasa con otros líquidos? La humedad en el aire también puede afectar los resultados (esto es especialmente cierto para el experimento de la cinta adhesiva). Háganos saber lo que observa en sus experimentos en el blog Comentarios a continuación.
referencias y Enlaces a más información
Algunas fotos y videos de destellos de luz triboluminiscente:
Otras instrucciones: Video de YouTube que ensaña la luz usando Duck tape: Radiografías de cinta adhesiva:
Artículo de Wikipedia sobre triboluminiscencia: Artículo de revista de investigadores de Towson State University (sí, ¡científicos reales estudian esto!):
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Click and expand the tabs below to get started. what you'll need
experimental procedure
Check out this video from Science Off Center and the St. Louis Science Center what's happening
When you run a plastic comb through your hair it pulls lots of very tiny particles called electrons away from your hair. We say these electrons have an electric charge, and when electrons (or other charged particles) move we call this electricity. If lots of extra charged electrons are stuck on the comb and not moving, however, we sometimes call this static electricity. This static electricity creates a force around the comb which can push or pull other charged materials, kind of like a magnet, and it turns out that water molecules are easily pulled by this force. That's why the stream of water from your faucet bends when you hold the charged comb nearby. The closer water is to the comb the stronger the force and the more it moves, but if the comb gets wet it can discharge, allowing those extra electrons to escape, thus there is no force left to pull on the water stream.
more detailed explanation
Everything is made up of matter, matter is made of atoms (which can combine to form molecules), and atoms are made up of protons, neutrons and most importantly for this experiment, electrons. The protons and neutrons are stuck together in the nucleus of the atom, while the much tinier electrons fly around outside the nucleus. It's kind of like the way planets orbit around the sun (the electrons are like the planets and the nucleus is like the sun), but electrons don't follow orderly paths like planets do, it's more like a cloud of electrons (called orbitals) surrounding the nucleus. What keeps electrons from flying away from the nucleus is a force called the electric field force. We say that electrons and protons have an electric charge, or just charge. Electrons have a negative charge (-), protons have a positive charge (+), and charged objects create an electric field that can attract or repel other charged objects (neutrons don't have any charge- they're neutral). Oppositely charged particles attract each other and the closer they are to each other, the stronger the field and the force of attraction. Particles with the same charge (such as two electrons or two protons) repel each other (the closer they are the stronger the field and repulsive force). [BTW- If this reminds you of the way magnets can attract or repel each other depending on their north or south poles and how close they are to each other, you're right. Electric and magnetic forces (and fields) are actually related to each other, so this is really called the electromagnetic force (and electromagnetic field). This is one of the four fundamental forces in nature (see the link below to learn more about this and the other fundamental forces that hold atoms together).] Different types of atoms (called elements) and the molecules they combine to form may be stronger or weaker when it comes to attracting and holding onto their electrons. In our case, the molecules that make up the plastic comb hold onto their electrons much more strongly than the molecules which make up your hairs hold onto their electrons. When you comb your hair, some of the comb's molecules get very close to some of the hair's molecules- so close, in fact, that the atoms in the comb actually start attracting or pulling on the oppositely charged electrons belonging to the atoms in the hair. Likewise, the hair's atoms also start pulling on the comb's electrons. It's kind of a tug-of-war battle, but with electrons (using the electric field force) instead of rope. Normally most molecules have the same number of negative and positive charges, (so we say they are neutral), but when you take the comb away from your hair some of the hair's electrons are actually pulled away, sticking to the comb's atoms instead (remember that the comb's atoms are stronger at attracting electrons). Thus the comb now has extra electrons- and extra electric charges- and your hairs have too few electrons, so we say the comb is now negatively charged and your hair is now positively charged. That's why your hairs are attracted or stand up if you bring the comb close to your head- because the opposite charges attract each other. The more you comb your hair, the more charges build up, and the stronger the electric field (and attractive force) will be. Charging an object this way is called contact electrification, or the tribo-electric effect (see the reference link below for more detail). This is also commonly called static electricity, but many scientists don't like this name, because electricity is defined as moving electric charges, thus static (non moving) electricity doesn't really make sense. Water molecules are made up of two hydrogen atoms and one oxygen atom attached to form a triangle shape, kind of like Mickey Mouse's head- oxygen is the face and the two hydrogens are his ears. All of the electrons in these atoms move around in such a way that the oxygen corner of the triangle is more negatively charged and the hydrogen corners are more positively charged. This kind of molecule is called dipolar. Since water molecules in a liquid are free to move around and rotate, when you hold your negatively charged comb near a stream of water, the positive (hydrogen) sides of each water molecule are attracted to the comb's electric field and rotate so that they point towards the comb. This means that the side of the water stream closest to the comb is more positively charged and the opposite side of the stream is more negatively charged. Finally, the electric field of the negatively charged comb attracts (or pulls) on the positively charged side of the water stream, while it also repels (or pushes away) the opposite (negatively charged) side of the stream, but since the positive side is closer, the attractive force there is much stronger and the stream of water is pulled towards the comb. If you move the comb to the other side of the stream the water molecules simply rotate again to point the opposite direction, so that the side of the stream closest to the comb is once again more positive, and thus the stream still bends toward the comb. By the way- if you hold a magnet near the stream of water nothing happens. It is neither attracted or repelled by the magnet. But that doesn't mean that water (or anything made mostly of water, like frogs or even people) can't be influenced by a magnetic field- you just need a really powerful magnetic field. In fact, if your magnet is strong enough you can even levitate a frog. Did you notice that if you get the comb wet, it no longer bends the water? The extra electrons that were stuck on the comb are able to move into the water and escape, thus the comb is no longer charged (and no electric field present). Also, if you wet the comb first, then run it through your hair, the water prevents it from grabbing electrons from your hair and charging up, so this doesn't bend a stream of water either. Even a microscopically thin layer of water on the comb, which can happen on a humid day, will prevent it from charging up (if you're having trouble making the experiment work, this may be the problem). variations and related activities
You can also bend the water stream with a rubber (Latex) balloon or plastic rod (PVC plumbing pipe works very well). Just charge them up by rubbing with your hair, a cotton towel or T-shirt or a piece of fur. Try lots of different materials. This related activity (and video) shows you how to charge a balloon or PVC pipe and make some other objects move. Check out the references below for more information about the tribo-electric series and charging different materials.
Try making the faucet drip instead of a continuous stream of water. Are the droplets attracted to the comb? And while you're in the bathroom anyway, take a small piece of toilet paper and dangle it vertically near your comb. It should also be attracted to the comb, because the comb's electric field induces a small electric dipole moment (like a charge) in the paper's molecules that is attracted to the comb. In fact, if you tear the toilet paper into really tiny pieces you can even use the charged comb to lift them right off a table or countertop, and even make them seem to dance! Here is a different way to do this experiment: references and links for more information
Other science website do this experiment:
More on atoms and contact electrification (static electricity): The tribo-electric effect (contact electrification) and tribo-electric series: The fundamental forces within an atom: Induced dipole moments or charges: Have a question or comment? Let us know at the bottom of the page.
Return to Try Science at Home This curious toy was first invented by René Descartes, an important scientist and mathematician in the early 1600's, and while his design has evolved into many different variations they all continue to amaze us while teaching some important scientific principles in a fun way. Click and expand the tabs below to get started. what you'll need
experimental procedure
Pipette "Submarine" diver:
Balloon "Fish" diver:
Ketchup packet diver:
what's happening
The pipette diver floats in the water at first because there is air trapped inside which makes it buoyant- just like the air inside a balloon or ping pong ball makes it float in water. When you squeeze the sides of the bottle you increase the pressure inside and that pushes more water into the pipette through the open hole at the bottom (you should be able to see it happen). This extra water makes it too heavy to keep floating (or more dense than the water in the bottle) and it sinks. When you stop squeezing the pressure drops and the extra water (and weight) flows back out of the pipette and it floats again.
The balloon "fish" also floats at first because their is a little air trapped inside, but this time when you squeeze the bottle there is no way to push any extra water inside (it's tied shut). But the balloon is made of rubber which is very flexible, so the pressure from the water outside squeezes the balloon and makes it a little smaller. The balloon still has the same weight, but now that everything inside is squished closer together (mostly the air molecules trapped inside) the balloon is more dense than the water and sinks. Stop squeezing and the balloon expands, becomes less dense and floats again. More detailed explanation
If this window doesn't open fully try closing and reopening the "What's Happening" window above while this window is open. The Earth's mass pulls other objects with less mass towards it's center (i.e. down). This is just the force of gravity that makes a ball fall to the ground, but the ball doesn't fall as long as you are holding it because your hand pushes up with a force that exactly balances the force of gravity pulling down. Of course if your hand pushes up with even more force you can make the ball move up. This is actually what's happening to our diver, we just need to understand what is causing these forces that make it move up and down. Obviously gravity is the force that makes it move down, but what force makes it move up? The surprising answer is actually gravity! But how can gravity make it move up and down? Okay, gravity doesn't directly push the diver up, but it is responsible for the force that does, which is called the buoyant force or buoyancy. As we said, the Earth's gravity pulls everything with mass down, including the water molecules in your bottle, and the weight (which is the amount of force of gravity) of all these water molecules trying to squeeze to the bottom of the bottle creates water pressure inside that pushes back and stops them. The deeper you go in the water the greater the pressure at that depth. Think of it like the cheerleaders making a pyramid. The cheerleaders on the bottom are being squished by the weight of the others above them, and must push back to keep them up. The cheerleaders in the second row have fewer above them, don't get squished as much and don't need to push back as much to hold up those above them. And of course the lone cheerleader on top isn't squished or pushing back at all. This water pressure doesn't only push on other water molecules, it pushes on everything inside the bottle as well as the bottle itself (and in every direction, not just up). So now we have a force that pulls the the diver down (its weight, which is equal to its mass multiplied by the acceleration due to gravity, i.e. W= M x g) and another force that pushes it up at the same time (its buoyancy, caused by the water pressure, which is also ultimately due to gravity). Whichever force is stronger determines the direction the diver will move. The weight of the diver is easy to measure, but how do we calculate its buoyant force? For the diver to move it must push any water molecules in its way aside or displace its volume (the amount of space it occupies). It turns out that the force needed to do this, or the buoyant force of the diver, is just the weight of the volume of water it needs to displace. This is called Archimedes Principle. To make things easier we can calculate the density, which is mass divided by volume (d=M/V), for both the diver and the water. If the density of the diver is greater than the density of water, then the weight of the diver is greater than its buoyant force in water and it sinks; if the diver is less dense than water the buoyant force is greater than its weight and it floats. The density of water doesn't change in this experiment (because water is incompressible- more on this later), so to move the diver up and down we must change its density instead. [BTW- water pressure pushes in all directions, so why does the diver go up if it's less dense than the water around it? Couldn't the water pressure just as easily push it down or sideways? Remember that pressure increases with depth, so at any depth the pressure on one side of the diver is always balanced by an opposite pressure push on the other side of the diver, i.e. they cancel out. But the water pressure pushing down on the top of the diver is always just a little less than the pressure pushing up on the bottom (because it's deeper), thus there is always just a little more force pushing up on the bottom than down or sideways and this is enough to insure that the diver (or any buoyant object) always floats upwards.] For the pipette diver we change its density by adding or removing mass while keeping its volume the same. When you first placed the pipette in the bottle of water it floated, so its density was less than the density of water. The pipette had only air inside and thus very little mass because there were very few air molecules (molecules in a gas are very far apart). When you squeeze the bottle it tries to squeeze the water inside, but the water molecules are already as close together as they can possibly get, i.e. we can't compress them any more, they're incompressible (which is effectively the case for all liquids). Gasses, however, are compressible since their molecules are very far apart and can easily be squeezed closer together. Thus the force of your squeezing the bottle increases the water pressure inside which pushes more water inside the pipette through the open hole in the bottom. The added water molecules increase the total mass of the pipette while the total volume inside stays the same (the air just takes up less volume now to make room for the added water volume), so the pipette density increases. Once enough water goes in to makes the pipette more dense than the water, it sinks. If you stop squeezing everything reverses- water flows out of the pipette, the air expands to fill more of the volume inside decreasing the overall density and the pipette floats once again. If you squeeze the bottle just hard enough you can force the right amount of water into the pipette to makes its density exactly equal to the water density and thus stop and hold the pipette motionless at any depth you choose. Give it a try! Watch the pipette closely as you squeeze the bottle and you should be able to see the water go in and out. This is exactly how a real submarine dives, surfaces or controls its depth in the ocean. Submarines contain ballast tanks that they can fill with water to increase their mass (and thus density) when they want to dive. To surface they blow air into the tanks, forcing the water out, which decreases their density and they float upwards. With just the right balance between air and water in the tanks they can control the density to remain at any depth they choose. The balloon "fish" also dives and sinks due to changes to its density, but instead of adding or removing mass we change its volume instead. Initially the balloon has just enough mass (mostly from the BB's inside) and volume (mostly due to the air inside) to make its overall density a little less than that of water, so it floats. When you squeeze the bottle and increase the water pressure inside it squeezes the balloon which then squeezes the air inside and reduces the volume of the balloon, i.e. it actually gets a little smaller. Since the balloon is closed nothing can go in or out (unlike the pipette diver), so the mass must stay the same even though the volume is smaller, and thus the density increases. If you squeeze the bottle and make the balloon small enough, the density will be greater than that of the water around it and it sinks. Stop squeezing and the balloon expands once again, its density decreases, and it floats back to the top of the bottle. Just as with the pipette diver, if you squeeze just hard enough you should be able to make the balloon stop and hover at any depth you like. We call this a balloon "fish" not only because it kind of looks like a little fish, but because this is very similar to the way a real fish controls how deep it swims in the water. Fish have a bladder inside their body that is filled with air (kind of like our lungs). They don't use it to breathe, but rather to control their density. Fish have muscles that can squeeze this bladder to make it a little smaller (just like you squeezed the bottle to make the balloon smaller) which in turn makes their whole body a little smaller and therefore denser when they want to sink to go deeper. To float up they just relax the muscles around the air bladder to make their body a little bigger and less dense. To hold any depth they squeeze their muscles just enough to keep the bladder the right size to match the density of the water. Can you make your "fish" perform all these movements? A ketchup packet usually contains a little air bubble inside so that it works just like the balloon in this experiment. The ketchup provides the mass (instead of BB's) and the flexible plastic or foil of the package allows it to change size as you squeeze the bottle. Finally, gravity also creates buoyancy in air and other gasses, which explains how helium and hot air balloons can float due to differences in density. In fact, this is true for all fluids, which can be composed of liquids, gasses or even solids (like sand) as well as mixtures of each. variations and related activities
More air inside the balloon increases the buoyant force, while adding more BB's makes it heavier, so by varying the size and weight of the balloons we can make it easier or harder for our diver to work. Try 2 or 3 different combinations in the same bottle. Another way to make it harder to operate is to leave a small amount of air in the bottle before screwing the top on. Now when you squeeze the bottle the increased pressure just compresses this air pocket rather than affecting the diver. Temperature also affects the density of the water (cold water is more dense than hot water), so a balloon which floats in cold water may sink if the water bottle warms up too much, perhaps by sitting in hot sunlight [to a lesser extent the warm water also warms the air in the balloon, which causes it to expand and increase its volume, thus increasing its buoyancy, so there is a trade off to be considered before determining if the balloon will now sink or continue floating. Generally speaking, the decreased density of the water with warming usually dominates, and the balloon sinks]. On the other hand, if you leave some air in the bottle, then warming the water also warms this air pocket, increasing its pressure, and effectively adding more "squeeze" force to make the balloon sink. A type of water thermometer named after Galileo uses this principle (see link below). You can also make the balloon sink by removing the bottle cap and blowing very hard into the bottle with your lips tight around the neck (as though you're trying to inflate it). This works best if your diver is very easy to move (i.e. its density is already very close to that of water). "Fizz-Saver" pumps can be used the same way. Buoyancy can turn raisins into divers, and you don't even need to squeeze the bottle. Buoyancy also makes Lava Lamps work. See the reference links below for more information. There are many other diver designs, including some that spin as they go up and down and one that works in reverse (i.e. it floats when you squeeze the bottle and sinks when you stop squeezing). You can even create a game to retrieve sunken treasure (and maybe think of a way to use buoyancy to retrieve real sunken treasures). Try other objects, such as restaurant salad dressing or honey packets and even little pieces or orange or lemon peels. Can you create a design of your own? You can also decorate your divers to make them look more like fish or squids- get creative! Check out the many links below for ideas. Can you use what you've learned in this experiment to design an instrument that measures the density of liquids? references and links to more information
History of René Descartes and Cartesian Divers:
More about density, buoyancy and Archimedes' Principle:
Other Cartesian Diver designs:
Make a reverse Cartesian Diver:
Make a game to retrieve sunken treasures: How submarines and fish use buoyancy to control their depth:
Make our cool Lava Lamp and raisins dance with buoyancy:
Galileo's thermometer: Make a hydrometer to measure liquid density: Have a question or comment? Let us know at the bottom of the page.
Put more than air inside a balloon and the science can get very interesting- perhaps even a little spooky! Click and expand the tabs below to get started. What you'll need
experimental procedure
Until we make our own you can watch Steve Spangler's video to help you get started. what's happening
When you begin to shake the balloon the penny bounces around inside as you would probably expect to happen, but what might surprise you is how quickly it will begin to roll once it lands on its edge. That's because a round shape like a coin rolls or turns very easily, and once it is rolling (or spinning about an axis like a wheel) it wants to continue spinning in the same direction. In physics we say a shape like this has a high moment of inertia, and this tendency for an object to continue spinning in the same direction (that's just what inertia means for a spinning body) is sometimes called gyroscopic stability. This is what keeps a spinning toy top upright, a gyroscope pointing in the same direction or a spinning bicycle wheel- or in this case your penny) from falling over (check out the videos below). But it gets better. Because the penny is now rolling inside the round wall of the balloon forces the penny to move in a big circular path, kind of like a planet orbiting the sun. We call this centripetal force, and the circular or rotational motion caused by this force is just another form of spinning or rotational inertia, this time about an axis through the center of the balloon, which is why it will tend to continue moving in the roughly the same circular orbit over and over again. Once it's orbiting inside the balloon if you move your hand back and forth just right and at a rate (or frequency) that exactly matches the penny's orbital frequency you can add more and more energy to its motion, which makes it go faster and faster! When you stop moving your hand the penny keeps rolling (that's its inertia again) until friction eventually slows it down, but since this friction force is relatively small and the penny is moving pretty fast it should keep rolling for a fairly long time. When you put a hex nut inside the balloon and start shaking the same thing happens. You might think that because the hex nut is not smooth and round like the penny it would not roll, but it turns out that this shape still has a fairly high moment of inertia and therefore does roll easily after all. While the penny rolled around inside the balloon almost silently, the nut makes a screaming sound as it rolls. This is because the corners of the nut bounce as they hit the balloon and cause it to vibrate, or move back and forth very quickly. As the balloon vibrates, that in turn vibrates the air molecules nearby which creates sound waves. The faster the balloon vibrates, the higher the frequency of the sound waves and the higher the pitch will be. As the nut moves faster it also has more energy and makes the balloon move farther with each vibration, which pushes more air and makes the sound louder. variations and related activities
Try to make the penny orbit in different directions (i.e. vertically, horizontally, etc.). You can also try different shaking motions to start the penny spinning. Once it is spinning fast, turn your whole body and the penny should continue to roll more or less in its original direction, just like a gyroscope. Try putting 2 pennies, or even 3, inside the same balloon. They might crash into each other at first, but after a few seconds you should see see all the pennies line up perfectly side-by-side and orbit together as one. We're not entirely sure why this works so well, so if you have a theory please let us know in the comment section below. Once you have your penny rolling really fast, gently toss the balloon into the air and observe what happens as the center of mass of the system changes. Experiment with different sizes of nuts. Does this change the sound? Just for fun you can draw a spooky face on your balloon with a marker to make a screaming ghost balloon. If you want to learn more about the strange things that happen when objects are spinning or rotating check out some of the links below. references and links to more information
Steve Spangler demonstrates the Screaming Balloon and more: Spinning tops:
Spinning bicycle wheel demonstration: Gyroscopes:
How does a bicycle stay up (disappointing hint- it's not really you doing it!): Have a question or comment? Let us know at the bottom of the page.
Click and expand the tabs below to get started. what you'll need
You will also want plenty of space to move around as you levitate objects. experimental procedure
what's happening
All materials are made up of molecules that are composed of atoms (except for pure elements which are just atoms). Atoms are made of even smaller sub-atomic particles called protons, neutrons and electrons. Protons and neutrons form the nucleus of the atom, while the much, much smaller electrons move around the nucleus. You can sort of picture the nucleus like the sun and the electrons orbiting the nucleus like the planets orbiting the sun (this isn't exactly correct, but it's okay for our simple picture). We say that electrons have a negative electric charge while protons have an opposite or positive charge, and these oppositely charged particles are attracted to each other (like a magnet that sticks to your refrigerator), which is what keeps the electrons in orbit around the nucleus (the neutrons have no electric charge and we can just ignore them for now). These electrons are so tiny and move around so easily that they can sometimes jump from one atom to another atom in the material, or even from an atom on one object to an atom on a different object. When two objects made of different materials, such as the latex balloon and the cotton or wool cloth, are rubbed together, the protons in each object not only attract their own electrons, but may begin to attract or pull on the electrons in the other object, sort of like a game of tug-of-war. If we now separate these two objects the one made of a material which can attract electrons the strongest may actually steal many electrons from the weaker material. This gives the "winning" object a lot of extra electrons, and thus a lot of excess negative electric charge, while the other object is left with the opposite or excess positive charge. This process is called contact electrification or triboelectricity, although it's more commonly referred to as static electricity. There are triboelectric series charts (see the reference links below) showing which materials can steal electrons from other materials, i.e. which will become negatively or positively charged upon contact with another material in the chart, but triboelectricity can be finicky, so it's not always clear which way the electrons will go in all cases, and sometimes the behavior just doesn't agree with the chart at all. To explain how electrically charged objects (or individual protons and electrons) attract each other scientists say that they create an invisible electric field or force in the space around them. This electric field can not only attract an object or particle with an opposite electric charge (like a proton attracting an electron), but can also repel a particle if it has the same charge, i.e. two electrons will repel each other. Thus similarly charged objects (either positive and positive or negative and negative) repel each other, while oppositely charged objects attract each other, sort of like the attractive and repulsive forces of magnets (in fact, magnetism is just another form of exactly the same fundamental force observed here- but that's for another activity). This is what's happening when you press the polyethylene plastic hoop against the tabletop surface, or rub the balloon with the cotton cloth. You have probably also noticed this when you rubbed a balloon on your hair. Rubbing objects together just brings more of their surfaces close enough so that the atoms in one material can tug at the electrons of the other (it's not due to friction, so you don't need to rub hard). When you pull them apart you each will have opposite electric charge: the plastic hoop and the tabletop have opposite charge, i.e. one is positive and the other negative and they attract each other (that's why they cling or stick together); and the ballon or PVC and the cloth also have opposite charge, one positive the other negative. It can be very difficult to tell which one is positive and which is negative, but as long as the plastic hoop has the same charge as the balloon or PVC wand (whether it's actually positive or negative) they will repel each other (of course if they are oppositely charged they will instead attract and perhaps even stick to each other). When you toss the plastic hoop in the air it starts to fall due to the pulling force of gravity, but your charged balloon or PVC wand produces a repelling or pushing force on the hoop. The closer you bring it the stronger that force will be, so that the hoop stops falling and rises up instead. If you hold the balloon or wand at just the right distance below the hoop you should be able to make it levitate almost motionless- bring it closer and the hoop rises, farther away and the hoop falls. Move your wand or balloon around and you can make the hoop dance and perform tricks! Different materials are classified as conductors if their electrons can move around easily through the material, or insulators if their electrons cannot move easily. Latex rubber, plastic and Styrofoam are insulators, while metals such as copper or the aluminum in a soda can are conductors. When we charge insulating materials like the Latex balloon by rubbing it, the separated charges stay put for a long time since their electrons can't easily move around, and that's why it remains charged. Metals are very different however, which is why electric wires and cables are made with metal conductors so that electricity (moving electrons) can flow more easily. These electric wires are covered with rubber or plastic insulation so we don't get a shock when we touch them. troubleshooting - what can go wrong
Contact electrification or triboelectricity can be very finicky, often due to various types of contamination or environmental factors which can influence the process. Thus you might have trouble charging your objects, or even get the opposite of what you expect to see. Some days it just doesn't want to work at all, especially on a very humid day. Moisture in the air can deposit a thin layer of water molecules on some objects which allows the static electric charges to move away. Oil from your hands can also contaminate objects in this way, so if your plastic hoop doesn't seem to work , try cutting off a fresh one. In our experience rubbing a Latex balloon or PVC pipe with cotton cloth and rubbing a polyethylene bag on a wooden surface should produce the best results, but if these combinations don't seem to work for you, try something different. You can substitute wool, fur or polyester fabric for cotton, and you can try different wooden surfaces (painted, varnished, waxed, bare wood, etc.). Some kitchen countertops (like Formica) may also work very well, but plastic tables do not. In any case, the more you practice the better you will get at levitation, so keep experimenting. And who knows- a little Wingardium Leviosa probably couldn't hurt either! variations and related activities
You can also use the electric field force from a charged balloon or PVC wand to move other objects. Lay an empty aluminum soda can on its side, charge up your balloon or PVC wand then hold it very close to the can without touching it. The can should begin to roll towards your wand, so be sure to move it away as the can rolls to keep from touching. Place your wand on the other side of the can and you can make it stop, then begin rolling the other direction. Notice that you didn't need to charge the can for this to happen! That's because metals like aluminum are conductors, unlike the PVC plastic or Latex balloon. When we bring an aluminum can or a metal spoon near a charged object such as a balloon, the electrons in the metal can move around easily. If the balloon has a negative charge, electrons in the soda can (which also have negative charge) are repelled (remember similar charges repel each other) and move as far away from the balloon as possible (i.e. to the back side of the can), leaving fewer electrons and thus a positive charge on the side of the can nearest the balloon. Since opposite charges attract each other, the can will move towards the balloon. The same thing happens when a metal spoon is held close to a balloon; if a balloon is hanging from a string and free to move, it will be attracted to the spoon. Your fingers are also conductors (though not as good as the aluminum in the soda can), so the balloon should also move towards your fingers or body. That's also why the polyethylene hoop likes to stick to your body! Have you ever noticed little bits of Styrofoam (like packing "peanuts") clinging to your hand or other objects? Do clothes cling to you or other clothes when you take them our of the dryer (i.e. "static cling")? Styrofoam peanuts (and clothes) can pick up an electric charge very easily by bumping into other peanuts (or clothes) or just about anything else, and thus will be attracted strongly to other objects- which you've probably noticed if you ever tried to pick them up! Try moving them around with your charged balloon or wand. The tiny beads inside a beanbag chair are also made of Styrofoam, so you if you have some you can put them inside a dry, empty plastic soda bottle and screw on the cap (if you don't have an old beanbag chair you can tear some packing peanuts or other pieces of Styrofoam into tiny bits instead). Now rub the outside of the bottle on your cotton shirt or hair and shake the bottle to transfer electric charge to the bits inside, then move a charged balloon or PVC wand near the bottle to see what happens! Also try moving a metal spoon, fork (or your aluminum soda can) near the plastic bottle filled with Styrofoam bits. Just as when you rolled an aluminum soda can above, electrons in the metal can move around due to the influence of the electric field from a charged object. Electric fields around conductors are much stronger near sharp points and edges, thus as you turn the spoon (or point your fingertips), the Styrofoam bits will experience stronger forces and move more quickly. If you rub a balloon on your cotton shirt or hair in a very dark room you may see sparks and hear crackling! The sparks are actually tiny lightning bolts, and the crackling tiny thunder claps! The electric field around your charged balloon is strong enough to move or even rip electrons from nearby air molecules, and the energy released as they crash into other air molecules heats the air to make the sparks and crackles. This is also what happens when air moves rapidly in clouds during a storm to make the really big lightning and thunder, and when you rub your feet on carpet and touch a doorknob or "shock" a friend. You might also see sparks at night when you rub against your blankets in bed. We can even use the force of an electric field from a charged object to bend water! Adjust the faucet in your bathroom or kitchen sink so that a very thin continuous stream of water flows (rapid dripping also works). Charge up a PVC wand, balloon or even run a plastic comb through your hair then carefully hold it close to the stream of water. Make sure your charged object doesn't get wet, however, as this will discharge it (electrons can move through water- that's why you never drop a toaster or hair dryer in the bathtub!) If this happens dry the PVC or balloon completely, then charge it up and try again. The stream moves because water molecules are dipolar, i.e. they have negatively and positively charged ends. There are even more electric charge activities and experiments in the links below. references and links to more information
More about triboelectricity, contact electrification and the Triboelectric Series:
Measure electric charge with a DIY electroscope:
Fun with static electricity videos:
More static electricity activities:
Just for fun, levitating a frog in a very strong magnetic field: Have a question or comment? Let us know at the bottom of the page.
Click and expand the tabs below to get started. What you'll need
experimental procedure
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