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!

• Dr. Electric's Microwave Oven Laboratory at http://www.discovery.panasonic.co.jp/en/lab/lab02mw/
• Professor Lee's Microwave Oven Laboratory at http://www.colorado.edu/physics/2000/microwaves/

  Little Lion Experiment

  The microwaves used in microwave ovens are specially designed to heat up water molecules since food is mostly water.

  Get two crackers that are the same size and type. Moisten one cracker with room-temperature water. Put both crackers onto a napkin and microwave them for 7 seconds. Safety note: wait 20 more seconds before opening the microwave door so that the heat will have a chance to spread out evenly over each cracker! Feel both crackers with your finger. Which one is warmer? Why?

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!

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!

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.

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 http://www.seasky.org/pictures/sky7b08.html.

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?

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?

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?