Thursday, December 15, 2005

How Do Microwaves Work?

When you drop a stone into a pool of water, you see waves. Ripples in the water bounce up and down. The waves form circles around the spot where the stone hit the water. The ripples start small but then they move away from the center, in bigger and bigger circles. The frequency of the waves represents how quickly they are bouncing up and down.

Microwaves are a type of radio wave. Appliances such as your radio, cordless telephones, cell phones, and television all function by radio waves. Radio waves are like water waves, but you can't see them.

In addition, radio waves work on a much smaller scale. Everything in the universe is made up of atoms (the fundamental building blocks of all matter). The most mobile parts of an atom are called electrons. When radio waves hit an object, they make the electrons in that object bounce around.

High frequency radio waves have more energy than low frequency waves do.

Microwaves are very high-frequency radio waves. They are used in cell phones, wireless Internet, and in microwave ovens.

The waves in cell phones and wireless Internet do not get very much electricity, so these waves are very weak. In contrast, lots of electricity runs through a microwave oven, so microwaves are strong.

Just as water waves make things move, microwaves make atoms move. The atoms bump into each other, and the resulting friction makes the food get hot.

In a microwave oven, a radio makes microwaves and sends them in one direction. They are aimed at a spinning fan that sits above or beside the food inside. Sometimes you can see the fan, but most of the time it is hidden behind plastic.

When the microwaves hit the spinning fan, the waves bounce off and hit the food. The microwaves then get absorbed by the fats, sugars, and especially water in the food. Once absorbed, the microwaves cause the electrons in the food to vibrate. This generates heat, which can then evenly heat up your food.

Microwaves can bounce around inside the oven. The metal walls of the oven keep the microwaves from escaping into the surroundings. Even though you can see the food while it's cooking, the microwaves won't bounce out of the glass door because the metal screen stops them. Still, it is not good to be too close to the oven when it is cooking.

For more fun information about the science of microwave ovens, you should explore these interactive websites!

Tuesday, November 15, 2005

Why Do Plants Wilt?

If you've ever forgotten to water your house plants, then you've probably noticed that they begin to wilt. Most of us naturally know that wilting plants need water, but exactly why is it that dehydrated (thirsty) plants wilt?

The answer is that plant cells contain many organelles (compartments), one of which is a very large vacuole (storage compartment) for water. When filled with water, this vacuole pushes out against the cell wall (a rigid layer which wraps around the plant cell to support it). This resulting outward pressure is called turgor pressure.

When it rains, or when you water a house plant, some of the water absorbed by the plant's roots is used to carry out cellular processes, some is used to transport nutrients (the plant's equivalent of an animal's blood circulation), and the leftover water is stored in vacuoles in the cells.

So, when a plant is well-hydrated, its vacuoles swell with water. Thus, the turgor pressure inside each cell is high. This supports the wall of each cell and makes the plant cells stiff. This stiffness is what allows plant stems to stand up straight (plants rely on turgor pressure since they do not have bones to support their "limbs" against gravity).

In contrast, when a plant gets dehydrated, it must use its vacuoles as a source of water since water is so important for every cell to function. So, some of the stored water must exit the vacuoles so that it can be used. This is similar to a town's water tower: when the town is well-supplied with water, the tower stays full, but when there is a water shortage, the stored water in the tower is drained out and used to support the townspeople.

As you can imagine, when the vacuoles are drained, they shrink and thus do not push outward on the cell wall anymore. This lack of turgor pressure causes the plant to wilt.

Little Lion Experiment:

Cut a grape in half and peel the skin off of it. If you don't have grapes, then cut a thin (1/4") slice of an apple. Notice how the fruit is rather stiff.

Next, to cause dehydration, cover the piece of fruit with salt for 10 minutes. The salt will draw some of the water out of the fruit. For the best results, scrape the wet salt off of the fruit and replace it with a new sprinkling of salt every 2 minutes.

Now, you have dehydrated the fruit cells so that their water vacuoles are depleted (i.e. they contain less water than they used to). This is similar to what happens when you forget to water your house plants. Feel the fruit to see how dehydration affected the stiffness of the plant. Can you explain your results with regard to turgor pressure?

Food for thought: if you left the grape in salt for a very long time, you'd end up with something similar to a raisin. A raisin, after all, is just a dehydrated grape! It still has the same amount of skin around it, but that skin is wrinkled because the volume of the raisin is much less than the volume of the original grape. This difference in volume shows how much water was lost. So, since grapes are so much larger than raisins, you can see that the main component of grape cells (and in fact all living cells) is water!

Saturday, October 15, 2005

Why Do Onions Make Us Cry?

Many people enjoy the taste of onions in their meals. Indeed, the average American eats about 18.3 pounds of onions each year. Onions are healthy components of the human diet because they contain vitamins B and C, protein, calcium, iron, and quercetin (an antioxidant, which helps to neutralize harmful substances in our bodies that cause tissue damage and aging). In addition to being full of nutrients, onions are low in fat and sodium.

However, if you have ever cut into an onion, it is likely that your eyes filled with tears. Why does this happen? How can we enjoy the taste and benefits of onions without the tears? Read on to find out.

When you cut into an onion, an enzyme (i.e. a molecule that speeds up chemical reactions) called lachrymatory-factor synthase is released into the air from the ruptured onion cells. This enzyme converts some of the proteins in the onion into sulfenic acids, eye irritants which are responsible for the flushing action of our tears. Sulfenic acids are also responsible for the strong odor of raw onions.

So, how can we enjoy the benefits and the great taste of onions without the tears? Here are several methods that can reduce the amount of sulfenic acids that reaches the eyes:

  • After peeling, put the onion in the refrigerator or freezer for a few minutes to slow the speed of the chemical reaction.
  • Run the onion under cold water while slicing, or cut it underwater.
  • Cook the onion before slicing.
  • Do not rub your eyes, because they will be coated in irritating compounds from the juice of the onion.
  • Cut the onion in a plastic bag with the bottom cut out.
  • Turn the vent fan on high and place your cutting board next to the stove top.
  • Try pouring a small amount of white distilled vinegar on your cutting board before slicing.

Over time, it is even possible to develop a tolerance for the chemical, reducing the amount of reaction.

Go on, put your new eye defense skills to the test with the help of a parent or other handy adult with the Little Lion experiment of the month!

Little Lion Experiment:

This onion soup recipe from the National Onion Association is full of flavor, and makes a tasty treat. To make it, you will need:

  • 4 large yellow onions
  • 6 tablespoons butter or margarine
  • 1 tablespoon sugar
  • 2 quarts reduced sodium chicken broth
  • Salt and pepper to taste
  • baguette French bread, sliced and toasted
  • Grated Romano cheese
  • An adult to help you

To begin, slice the onions, using any of the above methods to reduce eye irritation. Be careful with the knife, and always point the sharp part of the blade away from you when cutting. Melt the butter or margarine in a large saucepan that holds at least 4 quarts. Next, add the onions and cook over medium heat, stirring often, for 12 minutes or until tender and golden. Add sugar and stir for one minute. Next add broth, cover, and bring to a boil. Reduce heat, and simmer for 12 minutes. Season the soup with salt and pepper to taste.

Finally, ladle soup into bowls and top with toast and cheese. Enjoy!

Thursday, September 15, 2005

What Are MagLev Trains?

Engineers and scientists not only invent new modes of transportation, but they also look for ways to make existing vehicles faster, safer, quieter, and more energy-efficient (i.e. make them use less energy).

One area of current research is the MagLev train. MagLev stands for Magnetic Levitation. Demonstration MagLev trains have already been built in Germany and Japan, where they have reached maximum speeds of 250 to 350 mph!

This is still not as fast as commuter airplanes fly (~550 mph), but it is still a huge improvement over conventional trains, which travel at about 80 mph. So, you can see that a trip on a MagLev train would be about 3 to 4 times as fast as the same trip on a regular train! This is because MagLev trains don't touch the tracks, so only air resistance slows them down (vs. the large amount of friction between the tracks and wheels of a regular train). This also makes MagLev trains much quieter than regular trains.

Now, let's look at how MagLev trains work. Every magnet has two opposite sides: north and south. If you've ever played with magnets, then you know that opposites attract and likes repel. In other words, north and south attract, while two norths or two souths will push away from each other.

Imagine that you have one large flat magnet laying on a table so that its north side is facing the ceiling and its south side is flat against the table top. If you put a smaller magnet on top of the larger magnet so that their north sides touch, what will happen? The two magnets will repel each other. If this force is strong enough and if the small magnet is light enough, then the small magnet will levitate (float) above the larger one.

MagLev trains use the principle that we just discussed, but on a much larger scale. Most MagLev train designs rely on repulsion between magnets on the tracks and magnets on the bottom of the train.

In our tabletop example above, we got the small magnet to levitate but not to move forward. Thus, a power supply is needed to change the magnetic forces behind and in front of the train in such a way that the train is pushed and pulled forward.

How are the power supply and the magnets related? Unlike permanent magnets (e.g. kitchen magnets), the magnets used for MagLev trains are electromagnets (their magnetic forces are created by electricity). Since these electromagnetic forces rely on a power supply, their strength and direction can be changed by altering the power supply.

Current research is focused on making this power supply more energy-efficient, and thus cheaper to maintain. Once the price of operating the train is reduced, MagLev train tickets could be sold at reasonable prices to the general public.

Little Lion Experiment:

As objects move further apart, the magnetic attraction or repulsion between them gets weaker. To observe this relationship, obtain a few different strong refrigerator magnets. Tie a piece of string (about 8" long) onto a small metal paper clip. Then, tape the free end of the string onto the table.

Hold one refrigerator magnet next to the paper clip then raise the magnet until the string is pointing straight up. Slowly pull the magnet upwards one millimeter off of the paperclip. If the paperclip drops, then the magnet is fairly weak. If the paperclip stays suspended, then the magnetic attraction is still strong enough to fight the forces (mostly gravity, but also the tension in the string) pulling the clip downwards.

Continue moving the magnet upwards. Eventually, the paperclip will drop. This is when the magnetic force pulling it upwards becomes less than the forces of gravity and tension pulling it downwards.

These downward forces depend on the string and the paperclip, so they are the same no matter which magnet is used. So, if you use the same paperclip and string each time, then the distance at which the paperclip drops depends only on the strength of the magnet.

Monday, August 15, 2005

Why Do the Stars Change?

When you gaze up at the night sky on a clear night, you have probably been able to identify the North Star as well as certain constellations (recognizable groupings of stars) such as the Big Dipper and Orion.

Other famous constellations include the twelve zodiac signs, which are based on ancient mythology. The two zodiac constellations that are assigned to the month of August are Leo and Virgo. Oddly enough, these two constellations are not among the easiest to see this month.

The constellations most easily visible in August are: Sagittarius (The Archer), Telescopium (The Telescope), Lyra (The Lyre), Scutum (The Shield), and Corona Australis (The Southern Crown). For diagrams of these constellations, as well as information on their important features, visit

Stars don't actually travel across the sky, so then why does the night sky change according to the season? In other words, why can you only see certain constellations during certain months?

The answer is that the planets in our solar system revolve (travel in a circular path) around the Sun and rotate (spin). The Earth rotates towards its eastward direction, and each rotation represents one day.

The part of the Earth that faces the Sun experiences daytime, while the side facing away from the Sun experiences nighttime. Thus, the stars that we see on a given night are only those that face the nighttime side of the Earth on that particular night.

So, since we are moving but the stars are not, our position changes in relation to the constellations. To better visualize how the movements of the Earth affect our night sky, do the Little Lion Experiment as directed at the end of this article.

While this concept may seem strange at first, think about how the position of the Sun in our sky changes during the course of a day. It is not the Sun moving, but the Earth moving that causes the Sun to appear as if it were moving across the sky. Our view of other stars is like this except the movements are less obvious since they are so much further away from us than the Sun is.

The Earth rotates more or less in a sideways (versus upwards or downwards) direction. It is as if the Earth were spinning about a line running from the North Pole to the South Pole. This imaginary line is called the axis of rotation.

However, the actual axis is tilted a bit. This is similar to a top spinning when it is just starting to tip over. The tilted axis of Earth is believed to be a result of the Earth having been hit by a large object (like an asteroid) a long time ago.

Little Lion Experiment:

To make a model of our solar system, put a ball on the table to represent the Sun. Use an orange or plum to represent the Earth (which revolves in a counter-clockwise direction). Pick an object in the room (like a clock on the wall) to represent a specific constellation, while a spot on the ceiling directly above you can represent the North Star.

Put a small piece of tape on the fruit to represent where you are. Stick a straw into the fruit where the tape is, pointing diagonally upward. Imagine standing where the tape is on your model Earth. What you could see through the straw represents the part of the sky you see when you look outside.

By acting out how the Earth rotates and revolves around the Sun, you can see when you experience day and night, as well as how your view of the universe (represented by the room in which you are sitting) changes.

To compare your model to the actual changes in the night sky, find the North Star, as well as one or two constellations that are easy for you to spot. Then, track their positions in the night sky over the next few weeks (once per week is sufficient).

Using your model, can you see why the position of the North Star stays relatively constant, while the constellations seem to move across the sky?

Friday, July 15, 2005

What Are Sloths?

When many people see a sloth for the first time, they think that it is either tired or lazy. In fact, the word "slothful" means "lazy." Sloths are not actually weary or lazy, but many people make these false assumptions because sloths sleep so much (up to 15 hours per day!) and because they move at an incredibly slow pace.

Sloths are so sluggish because they are designed to live off of very little food (food is how animals get their energy). Since sloths do not eat many calories (energy stored in food), they have very little energy to carry out their bodily processes like digesting food and regulating body temperature. In other words, sloths have a very slow metabolism (the rate at which their bodies use energy).

There are two types of sloth: the two-toed sloth and the three-toed sloth. These names refer to the number of toes on the animals' forelimbs (arms). However, there are other differences as well. Two-toed sloths have longer legs, do not have tails, and are omnivores (they eat plants and small animals). In contrast, three-toed sloths have shorter legs, are equipped with tails, and are herbivores (they only eat plants). Both types grow to be 1 1/2 to 2 1/2 feet long.

Two-toed and three-toed sloths both evolved from the Giant Ground Sloth, an herbivore that was about the size of an elephant! For reasons that are still unknown, the Giant Ground Sloth became extinct in North America about 10,000 years ago. As a result, the sloths that we see today are native only to Central and South America.

In contrast to the Giant Ground Sloth, modern day sloths rarely go down to the ground. Instead, they spend virtually their entire lives hanging upside down in trees!

This upside down position is the reason that many of their internal organs (e.g. stomach and liver) are located in different places than they are in other mammals. In addition, a sloth's hair curves from its stomach to its back, which is the opposite direction of hair growth on most animals.

Speaking of hair, sloths have excellent camouflage (physical traits which help them to blend into their surroundings in order to hide from predators). Sloth hair is grey and brown so that it matches tree bark.

However, sloths often have a bluish-green appearance during rainy months because the extra moisture in the air allows algae to grow on their fur. Since the rainy season allows more leaves and moss to grow on the trees, having a bluish-green coat helps sloths to blend into their environment.

Little Lion Experiment:

Unlike most mammals, sloths allow their body temperature to fluctuate somewhat along with their environment. So, their bodies get colder at night and during the rainy season.

As a result, their digestion slows during these times. This is because their digestion processes are temperature-dependent. In other words, the warmer a sloth's body is, the faster it will digest food.

So, if sloths get cold enough, then they can not digest food quickly enough to survive. This means that sloths can actually starve in cold weather even if their stomachs are full of food!

To examine temperature-dependence, fill a Styrofoam cup with 2 inches of very cold water. Place a wooden toothpick into the water and leave it there for the rest of this experiment (it will reduce 'bubbling over' in the microwave).

See how much salt you can dissolve into the cold water. Remember, dissolved salt is invisible, so as soon as you see salt at the bottom of the cup, then stop adding salt! Intact salt means that you have dissolved all the salt you can at this temperature.

Microwave the cup for 10 seconds, then wait 15 seconds before opening the microwave door. Next, take the cup out of the microwave, carefully swirl it, then see if you can dissolve more salt into the water. Microwave for 10 seconds more, wait 15 seconds, and see if you can dissolve more salt. Note: do not repeat these steps again or else the water will become dangerously hot!

Do you notice a relationship between the temperature of the water and the amount of salt that can be dissolved in it?

Wednesday, June 15, 2005

What Are Honeycombs?

When you think of honeybees, you probably think of honey. However, most of us don't give much thought to the honeycomb, also known as a wax comb. This comb is an array of hexagonal compartments in which larvae (baby bees) develop. A queen bee can lay up to 3,000 eggs per day, so there are always thousands and thousands of larvae that need compartments in which to grow!

If you've ever seen a honeycomb before, then you may have noticed that it is composed of tightly-packed hexagons. Bees use this shape because it has a small surface area (how big the walls are) compared to its large volume (3-dimensional space that it contains). In other words, hexagons "wall off" a lot of space using only a little bit of wax.

Another way to look at constructing a bee hive is that wax is what is "costs" the bees to build a hive. Bees have to spend time and energy making wax, so it's not a good idea to waste it. Compartments are what they get out of their work. Since there are so many larvae that need room to grow, space is precious, so wasting it is not an option for bees!

Therefore, bees want to build the largest number of compartments possible by using the least amount of wax. Getting a lot by using the least amount of material is called efficiency.

The most efficient shape for boxing in a single compartment is a circle. However, circles are not that efficient if you have to make more than one compartment. This is because having circles next to each other (like a bunch of cookies on a dish) means that there will always be wasted space between the circles.

So, bees use hexagonal compartments, which contain almost as much volume as circular ones, but which do not waste any space. In other words, if you arrange hexagons in the right way, then there will be no space between the compartments, which means no wasted space!

Honeybees have been around for over 150 million years, but still, how did they manage to figure all this out? Well, they weren't sitting around measuring the surface areas of different shapes. Rather, different groups of bees tried different ways of building honeycombs. The bees that built the most efficient honeycombs were able to give more of their larvae a place to grow. So, that's how bees evolved to make hexagonal honeycomb.

Little Lion Experiment:

Get some play-dough or clay and roll out three smooth sheets which are about 5' across. Then, roll out a long coil and flatten it so that it is about 1/8' thick, 1' wide, and exactly 2 feet long. Using a butter knife, slice off the rough edges to make a 2-foot-long rectangle. Use a ruler to make sure that all parts of the rectangle are equally wide!

Cut the rectangle into three 8' strips. Stand a strip on its edge and bend it around to make a square. Use the second strip to make a triangle. Use the third strip to make a hexagon. Remember, you used the same amount of clay to make each shape, so all three have the same surface area.

Connect each of your three shapes to a 5' sheet so that you have three boxes without lids. Use a tiny bit of extra play-dough or clay to seal the cracks. Put your boxes over some newspaper in case they leak. Make sure that the boxes are still level with the table!

Now, we're ready to measure the volume. Fill the hexagonal box with sugar. This volume of sugar is equal to the volume of the box.

Then, carefully pour the sugar from the first box into the second box. You'll have leftover sugar since the second box has a smaller volume than the first box does.

Next, use the sugar from the second box to fill the third box. Judging by the amount of sugar needed to fill the second box versus the third box, which one has the larger volume?

Sunday, May 15, 2005

What Is Special About Dandelions?

You've probably seen dandelions before: yellow flowers which turn into white fluffy spheres. But, despite these interesting flowers, the part of the plant that the dandelion is named after is actually the leaf! The sides of dandelion leaves have a zig-zag shape because they have very deep dents in them. This zig-zag shape reminded early Europeans of lion's teeth, so they called the plant "dent-de-lion," which means "lion's tooth" in Old French! The name "dent-de-lion" then became modernized into "dandelion."

Although dandelions originated in Europe, they were brought to many other regions of the world and now can be found virtually anywhere! This is because dandelions can survive and thrive in many different environments, including some that are harsh enough to kill most plants. In other words, the dandelion is one tough plant!

In fact, the toughness of dandelions makes them very hard to get rid of. If you simply pull off the leaves and flowers, the plant will regenerate (re-grow), much like a starfish can regenerate if it loses its limbs.

As for the flowers, they are actually composed of many tiny flowers arranged in a circular bunch, which is typically 1 to 2 inches wide. This is called a composite flower. In fact, each composite flower of a dandelion is made up of hundreds of tiny individual flowers! This explains why each composite flower can produce hundred of seeds (one per flower).

Another example of a composite flower is the sunflower. The difference (other than size) between sunflowers and dandelions is that the small flowers in the middle of a sunflower look like little buds. They are greenish-brown instead of yellow and do not look like they have petals. These central flowers are called disk flowers.

The outer flowers (the ones that are bright yellow) are called ray flowers. Dandelions are unique in that they are completely made up of ray flowers. In other words, they don't have any disk flowers. This is why all of the flowers in a dandelion look the same.

Another unique characteristic of dandelions is that they don't rely on insects to carry pollen from one flower to another. This process is called fertilization, or cross-pollination. In contrast to most plants, dandelions can fertilize themselves. This makes it even easier for them to reproduce, making them even better weeds!

Furthermore, the seeds have a unique way of spreading themselves around. You have probably noticed that dandelions become white and fluffy after they have bloomed. In fact, this transformation from the yellow composite flower to the white "snowball" form can occur overnight!

Later on, some of the "fluff" blows away in the wind. These fluffy pieces are actually dandelion seeds being carried by tiny white "parachutes" which float well in the wind. This helps the plant to spread its seeds over a large area, which makes it more likely that some will land in a nice patch of soil and be able to grow into new dandelion plants.

Little Lion Experiment:

To see just how effective these "parachutes" are, find a dandelion in its white fluffy form, and pull off the fluff. Pull slowly so that the seeds stay attached to the fluff! Then collect some similar-sized seeds (basil seeds work well for this). Now that you have two sets of seeds that are similar in size, shape, and weight, you can be relatively certain that any differences in how far the seeds travel will be due to the dandelion's parachute (rather than its size, shape, or weight).

Go outside on a windy day and toss the basil seeds up into the air. Watch them fall and notice how far (horizontally) they travel form where you are standing. Do the same with the dandelion seeds. Notice how much further they travel.

Now, can you see why dandelions sprout up in odd places such as cracks in the sidewalk? You don't see basil plants growing there! Seeds that travel far and wide are able to end up in environments much different than those in which they started. So, if you had a basil plant and a dandelion in a garden, where would you expect to find the next generation of basil plants? Where would you expect to find the next generation of dandelions?

Friday, April 15, 2005

What is Fool's Gold?

You've probably heard of "fool's gold" before, but what exactly is it and how does it differ from real gold? The technical name for fool's gold is pyrite. Like real gold, it is brass-colored, hard, and shiny. However, it is not made out of gold, which is why it's not nearly as valuable.

Pieces of pyrite have jagged edges and can sometimes form cubes. Sometimes pyrite also has a grain (sets of lines, just like in wood). Pyrite can be found right here in Pennsylvania, but it is also located in other states, as well as in Mexico and Europe.

True gold is an element. Elements are the smallest building blocks of everything in the universe. They are made of positively-charged particles (protons), negatively-charged particles (electrons), and neutral (non-charged) particles called neutrons. The only difference between different elements is how many of each type of particle they contain.

Besides gold, some other elements that you may have heard of are: silver, iron, mercury, and oxygen. As you can see from that list, elements can be solids, liquids, or gases.

The smallest piece or unit of an element is called an atom. Atoms can combine with each other to form molecules. Some molecules (like oxygen) are just made up of one element. The oxygen that we breathe is written as O2, since there are 2 atoms of oxygen in each molecule, and the symbol for oxygen is O. In other words, oxygen atoms are floating around in the air in pairs.

In contrast to O2, most molecules are made up of two or more different elements. For example, you may have heard water referred to as "H2O." This means that each molecule of water contains 2 hydrogen (H) atoms and 1 oxygen (O) atom.

You might be wondering why we don't write water as H2O1. It is just a scientific custom to not write 1 when there is only 1 atom of a given element in the molecule. By the same token, you can think of your hand as Finger5Palm since each hand is made up of 5 fingers and one palm.

Make sense? Now let's apply what we just learned and figure out the symbol for fool's gold! In contrast to real gold, pyrite is made of the two elements iron and sulfur. The symbol for iron is "Fe" and the symbol for sulfur is "S." Each molecule of pyrite is made up of 1 atom of iron (Fe) and 2 atoms of sulfur (S). So, pyrite is written as FeS2. In case you were wondering, the symbol for real gold is Au.

Little Lion Experiment:

When pyrite mixes with acid rain, it dissociates (comes apart) so now the iron and sulfur are separated from each other and are no longer grouped into molecules of pyrite. When molecules dissociate, you can't see them anymore since they are broken up into such tiny pieces. So, the solutions (mixture) is clear.

When this solution mixes with groundwater (which isn't acidic), the iron can't remain in the solution and so it sinks to the bottom. But since it is exposed to water and air, it rusts. So, you are left with a rust-colored gel from the wet rusted iron. You may have seen this on rocks at the bottom of streams.

Most people don't have pyrite at home, so we're going to use antacids, which will behave the same way as pyrite does in this experiment. Ask your parents for an antacid tablet (like TUMS or Maalox). This experiment will be easier to see if the tablet is colored instead of white. If you don't have antacids, then ask for a calcium vitamin.

Break off a pea-sized piece, place it between two paper towels, then use a spoon to grind the tablet into a very fine powder. Put the powder into a cup. Add a teaspoon of water (this is like groundwater). Mix, and notice how the dust doesn't dissolve (you can still see it). To mimic acid rain, add a teaspoon of lemon juice (this is an acid). Mix, and see if some of the dust dissolves. The solution should become more transparent (see-through) since there is less powder floating on top.

Tuesday, March 15, 2005

How Are Rabbits And Hares Different?

This month, you'll probably see a lot of Easter decorations around. So, let's have a look at what makes a rabbit a rabbit, and a hare a hare. Baby rabbits are born with their eyes closed and without a fur coat. Rabbits build nests in which to care for these very fragile newborns. In contrast, newborn hares are fully-developed (with open eyes and coats of fur). Hares do not build nests.

Sometimes common names can make the distinction between rabbits and hares a little fuzzy (or furry as the case may be!). For example, black-tailed hares and white-tailed hares are commonly called jack rabbits, even though they are actually hares (not rabbits). The snowshoe hare is commonly known as the snowshoe rabbit. Cottontailed rabbits, however, are actually rabbits.

So, how did the snowshoe hare get its name? The answer is that, in the winter, it grows very long fur over its feet, which makes them look like snowshoes. Just like snowshoes give people a wider base to walk on, the extra fur on the hare's feet gives them a wider base. This helps the hare run more easily through the snow by not getting bogged down as deeply in it. Rather, it glides over the surface of the snow as it runs.

As its name suggests, the snowshoe hare is completely white (except for the tips of its ears) in the winter, but the white-tailed hare can turn completely white too if it lives in a very cold environment. So, sometimes what seems like a snowshoe hare might actually be a white-tailed hare.

In the warmer months, the hares shed their white coats and replace them with grayish brown coats. This makes sense when you think about the forest when it is not covered in snow. If a hare is running through the forest, it is likely to be seen against tree trunks, dead leaves, and rocks. Since these items are brown and gray, the hare can blend in if it too is brown or gray.

Why does environment make a difference in fur color? The answer is that animals survive better if they can hide from their predators (animals that eat them). One common way to not be noticed is to blend into the background by matching it. In nature, this is called camouflage.

Let's think through why different fur colors correspond to different seasons. In very cold regions, the ground is often covered in snow. So, to blend in with its snowy environment, the snowshoe hare and the white-tailed hare grow white coats of fur. In contrast, warmer environments for the hares have darker backgrounds (like mountains and deserts). So, a brown or gray coat of fur is the best camouflage in these warmer areas.

Little Lion Experiment:

Animals don't decide what color to be; rather they have evolved (adapted over time) to have this camouflage. Basically, the animals that blended into their environments were able to hide from predators, so they survived much more often than those that didn't blend in well. As a result, the hares that survived were those who happened to make coats that matched their environments, while the animals that got caught by predators were usually the ones that "stuck out" and were therefore easier for predators to find. Over time, the only families of hares left were those who blended in with their environments.

You don't generally see many wild animals in the winter, but as the seasons change, you will see many more animals (like birds that had flown south for the winter) returning to this area for the warmer months. You will also see animals that stayed here, but did not leave their shelters very often during the winter. As you look around, try to spot other examples of camouflage in the animals that you see. Think about where those animals usually live (as opposed to where they are when you happen to see them) in order to see how their bodies blend into their environments.

Tuesday, February 15, 2005

How Do Animals Cope With The Winter?

When you come inside after a walk in the snow, aren't you glad that you have a heater in your house? What would life be like without a heater? This challenge is faced by wild animals every winter.

It is very difficult to survive in the winter for two main reasons: the cold temperatures make it harder to stay warm, and there isn't as much food available (since most plants don't grow in the winter, and many animals migrate to warmer areas). So, animals either need to avoid the cold weather, or find ways to survive in it.

The most common strategy to survive the winter months is called hibernation, in which the animal goes into a deep sleep-like state until the weather becomes warmer. This allows the animal to avoid the cold weather without having to move to a warmer climate (like birds do when they migrate south for the winter).

Hibernation is more than just sleep. It is a way to conserve energy by slowing down all of the body's processes. The animal's body produces less heat so its body temperature gets colder, and the animal also breathes much more slowly. These two bodily changes, along with the fact that the animal isn't moving, allow it to use up much less energy than it does when it is awake.

This is important since animals get their energy from food, and obviously the animal is not eating any food while it is asleep! But if the animal doesn't eat while it hibernates, then how does it get energy? Hibernating animals eat enormous amounts of food right before they hibernate. This extra food energy gets stored as fat (bears can gain 40 pounds per week when they are preparing to hibernate!). Then, once asleep, their bodies use the extra fat for energy. Since the animals' bodies are in "slow mode" during hibernation, they do not require very much energy, and so the fat contains enough energy to sustain the animal through the winter.

Humans cannot hibernate, and so we need to eat every day, but hibernating animals are able to survive weeks or even months just by getting energy from their stored fat. Humans aren't the only animals that don't hibernate though. Grey squirrels, red foxes, and wild turkeys are just a few examples of other non-hibernators.

After you categorize an animal as a hibernator or non-hibernator, it is important to ask what type of hibernation it uses. This is because there are two kinds of hibernation: deep hibernation, and a more mild version called torpor. Deep hibernation is also called true hibernation since it is what we normally think of (sleeping through the whole winter without waking up) when we hear the word "hibernation." Examples of deep hibernators are: box turtles, toads, woodchucks, and garter snakes.

In contrast, when an animal is in torpor, it can wake up occasionally to look for food, then go back to sleep. In fact, some animals perform their normal activities during the day and just use torpor at night. In addition to being able to wake up easily, an animal in torpor has a higher body temperature (about 60F) than it would if it were in deep hibernation (around 41F, which is very close to the temperature of your refrigerator!). Black bears, skunks, and raccoons are examples of animals that use torpor during the winter.

Little Lion Experiment:

Get out a small pot and a thermometer that goes down to 40F (5C) or lower. If you don't have a thermometer like that, then put some cold water in the fridge, which is almost exactly the same temperature (41F) as a deep hibernating animal. Put a cup of warm water on the kitchen table. Let both cups sit for 20 minutes. Make some ice cubes (ask an adult if you need help).

Next, put an ice cube into the pot. Put the pot on the stove over low heat (get an adult to help you with this step). The ice cube will begin to melt into water. Keep checking the temperature of the water with your thermometer (or compare it to the refrigerated water) to see how long it takes for the water to reach 41F. We'll call this the "deep hibernator time." Also note how much longer it takes to heat up to 60F (the body temperature of an animal in torpor). We'll call this the "torpor time." If you don't have a thermometer, then you can just wait until the water is almost as warm as the room temperature water. Also record how much more time it takes to warm up to 98.6F, our body temperature (any household thermometer should be able to detect that temperature). We'll call this the "human time."

The amount of time it takes to reach a given temperature is directly related to the amount of energy (heat) that is needed to warm up the water to that temperature. So, the "deep hibernator time" shows how much energy is needed to go from freezing (which is about how cold it is where the animal is hibernating) to the animal's body temperature. Similarly, the "torpor time" shows how much energy is needed to go from freezing to that animal's body temperature, and the "human time" shows how much energy is needed to go from freezing to our body temperature. More importantly, the difference between the "human time" and one of the other times shows how much energy those animals are saving by only warming their bodies up to 41F or 60F instead of normal body temperature.

Saturday, January 15, 2005

How Do Snowflakes Form?

Snowflakes are a beautiful part of winter. You probably know that snow is a frozen version of rain, but why does snow fall in flakes rather than in drops? In other words, how do snowflakes form?

Like rain, snowflakes are formed in clouds (which are made of water vapor and tiny drops of liquid water). Since water freezes at 32 F, the water in clouds can freeze if the temperature is 32 F or below.

You may have noticed that snowflakes can have various shapes. Some look like typical intricate snowflakes (called dendrites), others look like long needles or tubes, while others look like hexagonal (six-sided) plates. If these plates have indentations (notches) in them, then they are called sector plates.

What determines the shape of snowflakes? The major factor is temperature, but snowflake shape is also affected by wind, humidity (how much water vapor is in the air), the amount of dust in the clouds, and the altitude (height) of the clouds.

These conditions are important because they determine how the water molecules (H2O) in a snowflake will be arranged. Whichever arrangement forms the most easily under a given set of conditions is the one that will happen in most of the snowflakes that day. This explains why, on a given day, most snowflakes look similar, but you can always find a few odd ones.

Since some conditions (such as wind currents) change so quickly, each snowflake is usually a tiny bit different than its neighbors. It is possible for two snowflakes to be identical, but this doesn't happen very often. Even if two snowflakes look identical, they are probably a tiny bit different. For example, one snowflake might have a few more water molecules in it than the other snowflake does, but your eyes can't see such a small difference.

As a general rule, there are five different snowflake shapes. Each one is found most commonly within a certain temperature range, as shown below:

Thin hexagonal plates 32-25 F
Needles 25-21 F
Hollow columns 21-14 F
Sector plates 14-10 F
Dendrites 10-3 F

Table adapted from

Think about the first snowfall of the winter. It usually looks like hexagonal plates or needles. This makes sense since the first snow usually falls when the temperature outside has barely dropped below freezing. The prettiest snowflakes (dendrites) tend to fall in January and February since these months are the coldest.

Little Lion Experiment:

On a day when it is snowing, put a piece of black construction paper in the freezer for 15 minutes or more in order to chill it. Then, go outside and hold the piece of paper so that snowflakes land on it.

The black color of the paper should allow you to easily see the shapes of the white snowflakes. However, the paper may begin to warm up after a while. If the snowflakes are melting on the paper, then you can cool the paper down by simply setting it on the ground against some snow, or standing over it so that it lies in your shadow.

Examine the snowflake shapes and try to figure out which of the five major types you have in front of you (there may be more than one shape on the paper). Repeat this experiment on other days when it is snowing. Try to do it on days with different temperatures (like 10 F, 20 F, and 30 F) so that you can see the different snowflake shapes that form at various temperatures.