Why Is It Often Warmer On Cloudy Days?

Why would clouds make it warmer outside? First we have to know what a cloud is made of. We see them all the time, we know rain comes from them, and we've probably pointed out some that look like animals or other shapes, but we may not know exactly how they are made.

It starts out when water from lakes, rivers, ponds, streams, and other water on the ground evaporates into the air. To say that the water evaporates means that some of the water leaves the ground after being heated by sunlight, and is carried by the air in very tiny droplets or as water vapor (gas) that cannot be seen with the naked eye.

You may have heard that warm air rises. The warm air close to the earth that carries the water vapor is an example of this. As the air rises, it cools, losing the heat that kept the water droplets suspended in the air. This cooling causes the water vapor to condense (turn back into liquid droplets). These droplets land on tiny specks of dust in the air. In other words, the water is no longer carried invisibly by the air, but instead, it clings to the dust particles. Groups of these wet particles make clouds.

How do clouds make it warmer outside if a cloud is only water droplets clinging to dust in the air? Actually, the clouds don't make it warmer outside; clouds keep it warmer outside.

A blanket of clouds covering the sky is a little like a blanket that you use to stay warm in the winter: the blanket holds in heat. Sunlight is the source of energy for the earth, and some of that energy is in the form of heat. On days when there are no clouds, heat from the sun can enter and leave the atmosphere without anything getting in the way. When it is cloudy, the clouds absorb (hold) some of the heat so it can't escape. Clouds also reflect some of the heat back towards the earth.

So, on a cloudy day, some energy from the sun gets into the atmosphere through the clouds, but can't get out again. When this happens, the heat builds up during the day, so it gets warmer outside. On days when there are only a few hours of daylight, the sun doesn't have much time to send some of its heat energy through the clouds, and not very much heat builds up. That's why, even on cloudy days, it's still cold out in the winter.

Sometimes it gets even warmer on cloudy days because of advection. Advection is the movement of heat, cold, and moisture when air moves (when there is wind). When warm air from a tropical climate moves into a cooler area on a cloudy day, the clouds keep in the heat just like they keep in the heat from the sun.

Since warm air can hold water vapor better than cooler air can, clouds that are very high up in the cooler part of the atmosphere do not have as much water, and so they are not as thick. Since thinner clouds let in more light and heat energy from the sun, it is not as warm on a day with high, thin clouds as it is on a day with a low, heavy cloud cover.

To summarize, clouds are made of droplets of water that cling to specks of dust in the air. Some heat energy from the sun can make it into the atmosphere through the clouds, but the clouds trap the heat in by reflecting and absorbing it, causing the air inside the cloud blanket to warm up throughout a cloudy day. Warm air moved by advection can bring heat into an area that will be held in if there are clouds. High, thin clouds do not hold in heat energy well as lower, thick clouds do.

Little Lion Experiment:

In order to see how clouds form on particles in the air, you will need:

• black sheet of paper
• glass jar or mug
• flashlight
• clear bag with ice
• confectioner's sugar

Steps:

1. Tape a black sheet of paper to one side of a glass jar or mug.
2. Have an adult boil about a cup of water then fill the jar or mug part of the way with boiling water.
3. Immediately sprinkle a small amount of confectioner's sugar into the top of the jar.
4. Quickly cover the jar with the bag of ice. Turn out the lights and shine the flashlight into the jar.

You should be able to see a cloud forming inside of the jar as the warm water evaporates, rises, and condenses onto the particles of confectioner's sugar when it reaches the higher air cooled by the ice. You may also see the water condense directly onto the sides of the jar or mug instead of onto the particles, but keep in mind that there is no container for real clouds; only dust particles.

This experiment was adapted from Teacher.net Lesson Exchange; http://www.teachers.net/lessons/posts/14.html

How Do We Hear?

There are so many diverse and interesting sounds in our daily lives that we tend to focus on the sounds themselves, but never really stop and think how we are able to hear them. What exactly is a sound anyway? In a nutshell, sounds are how our brain perceives waves that enter our ears.

Believe it or not, there is nothing inherently noisy about sound waves! The waves are the result of vibrations. For example, when you pluck a guitar string, it vibrates at a certain frequency (frequency is basically how quickly something vibrates). This causes the air around the guitar to get compressed (pushed together) in some areas, while the other areas expand.

Why does this happen? First, keep in mind is that, even though we can't see them, there are billions of molecules (tiny particles) floating around in air. Now, if you carefully watch a guitar string, you can see it go up and down very quickly when you pluck it. So when the string is moving towards you, it bangs into the air molecules and pushes them forward (thus compressing them). When the string moves away from you, it allows the air to expand. This pattern continues as the string vibrates, so you get alternating areas of compressed, expanded, compressed, expanded, etc.

This is like waving your hand in a pool of water. You hand moves at a much slower frequency than a guitar string, but it is a vibration nonetheless. If you've ever done that, then you know how difficult it is to move because your body spends so much energy pushing the water molecules out of the way.

You may have also noticed that waves ripple outwards. This is because the water near your hand gets pushed forward when your hand moves toward it, and it is allowed to expand when your hand moves away from it. The water waves that occur when your hand vibrates in water are similar to sound waves rippling outwards when something vibrates in air.

So, now that we understand what sound waves are, we can see that sound itself is not a result of plucking a string, banging a drum, etc. Only the waves are what result from those vibrations. Sound is just how our brain interprets those waves. It categorizes them according to their frequency, with high frequency (fast waves) sounding high-pitched like a violin, and low frequency (slow waves) sounding low-pitched like a bass.

When sound waves enter our ears, they cause bones in the ear to vibrate. Then those bones cause the fluid that lies in our inner ear to vibrate (like when you wave your hand in water).

Our inner ear also contains many tiny hairs along its surface. Each hair is programmed to respond to a certain frequency of waves in the ear fluid. When specific hairs come in contact with their "favorite" frequency, they send messages to the brain so it will know that that particular frequency has just entered the ear. These signals are interpreted as pitch. How is this amazing sensitivity achieved?

Our hair cells are basically arranged in a line. Each frequency "peaks" (is most intense) at a certain hair cell location, so each hair cell can respond to the one and only one frequency: the one which peaks where that hair cell is!

High frequencies tend to fizzle out quickly, so they only reach the hair cells that are close to the outside world. So, it should be no surprise that these hair cells respond to high frequencies. Low frequencies travel much further and "peak" further inside of your head. So your innermost hair cells are programmed to respond to low frequencies.

So, the lower a sound, the further inwards it peaked in your inner ear. The higher a sound, the further outwards it peaked.

Little Lion Experiment:

Stretch a rubber band around your thumb and index finger. Pluck the rubber band and notice the pitch. Stretch the rubber band by moving your thumb away from your index finger. What happens to the pitch now? Can you guess if the frequency is higher or lower?

After your pluck it, the band will keep vibrating but it won't move as far up or down (the height of the movement is called amplitude, and it corresponds to loudness). The frequency, however, shouldn't change (be careful not to move your fingers though!). If the frequency does change, then the pitch will change since frequency is interpreted by your brain as pitch. So, you can observe the frequency just by listening to see if the pitch changes over time! That allows you to see that the frequency stays the same even though the amplitude decreases.

Why Doesn't Candy Spoil?

It's that time again.. Happy Halloween everyone! With all those sweets, it's a good thing we don't have to fit them all in the refrigerator! Since we have to keep most of our food cold in order to prevent it from spoiling (you wouldn't want to leave milk out on the table all day!), then why don't we have to refrigerate candy?

First, let's look at why food spoils. For the most part, it is due to the growth of bacteria (microscopic life forms, each made of one cell). Bacteria naturally exist on everyone and everything, including food. Most of these bacteria are harmless, which is why we don't get sick from eating food in general. But, if bacteria are allowed to grow out of control then our food can become rotten.

Now, the question is: why can't bacteria grow effectively on candy? The answer is that there is too much sugar for them. Most bacteria need a small amount of sugar in order to survive, but if they are surrounded by too much of it, then they begin to dry out like raisins. This is because water flows toward a state of equilibrium (balance). The technical term for this is osmosis (pronounced "oz-MOSE-iss"). Water reaches equilibrium between the cell and its surroundings when the same number of molecules is dissolved in each place (dissolved substances are called solutes). The reason for this is that solutes take up space, so there is less room for water in the mixture. Water then flows by osmosis to make up for this difference.

Cells contain a lot of water, but there are also plenty of solutes in the cell. If there is an equal amount of solute inside of the cell as outside of it, then water is already in equilibrium. This is called being in an isotonic environment.

If there are more solutes outside of the cell, then that means less water, so water will leave the cell, and so the bacteria will become shriveled and die. The term for this is a hypertonic environment.

If, on the other hand, there are less solutes outside the cell, then there is more water outside, so water will flow into the cell, which can cause it to swell or even burst. This is called a hypotonic environment.

Bacteria have ways of dealing with slightly hypertonic or hypotonic environments, but most cannot deal with extreme situations, and so they shrivel up when they are surrounded by too much sugar or salt. This is why people used to salt their fish before refrigerators were invented. [Safety note: wet sugary foods (like an open jar of jelly) do need to be refrigerated, so don't stop storing food in the refrigerator or else some fungi, which are not bacteria, could grow in it at room temperature!]

Little Lion Experiment:

Bacteria are not unique in their responses to osmosis, but there are some differences among other types of cells. For example, all cells can become dried out, but plant cells like hypotonic environments more because the inward flow of water helps their cells to remain rigid, which is why healthy flowers don't wilt.

To see the effects of osmosis on plant cells, take a grape and cut it in half. If possible, peel the skin off of each half. Obviously, the halves would line up if you were to put them back together right now. Next, totally cover one half of the grape with sugar, and put the other half in some water. Leave them sit for five minutes, mixing the sugar once in a while so the grape is always touching dry sugar. Thought question: why did the sugar touching the grape get wet?

Which situation is hypertonic, and which is hypotonic? Knowing what you know about how plant cells respond to osmosis, which half do you think will shrink? After five minutes, take the grape half out of the water and put it on a napkin. Brush the sugar off of the other half (DON'T rinse it, or else you will be soaking it in water!!!). Line up the two halves to see if your predictions were correct.

How Does Memory Work?

As we start the school year, we are going to learn many new things. We may forget some of that information after a short period of time, but we will remember some of it for years after we learn it. Have you ever wondered why certain memories stay with you for years, while some memories fade away after only a few minutes or hours?

Think of a few events in your life that happened years ago. Your mind probably conjured up something that was relatively significant to you either because it was an important day in your life (like a birthday or holiday), or something to which have an emotional attachment (like a big surprise or an embarrassing moment). You are able to remember these events so long after they occurred because they are stored in your long-term memory.

However, some information is stored only in short-term memory. These are things which we need to know for only a short time after we first learn them. For example, when you look up a new phone number in the telephone book, you can usually remember it long enough to walk over to your phone and dial the number. However, you probably wouldn't remember the number a day later. Saying something over and over in your head, or reading it many times reinforces the items in your short-term memory, and this is how studying for school works.

There is another type of memory called sensory memory, which involves remembering how something looks, sounds, tastes, smells, or feels. This is how most memories start out, but this type of memory can only be stored for less than a second unless it is quickly stored in short-term memory. Sounds and images are transferred most effectively, so if you hear the word "pizza," then the image which comes to mind is much sharper and clearly-defined than the vague (general) memory of how it tastes or smells.

Short and long-term memory involve different processes in the brain, but they are connected and they do interact. For example, the long-term memories that you recalled a moment ago are still fresh in your mind. This is another way of saying that they have temporarily been retrieved to your short-term memory.

Similarly, short-term memories can be stored as long-term memories if they are repeated or rehearsed enough over a long period of time. Taking our phone number example one step further, you know your own telephone number and maybe your best friend's number very well. This is because you have said, written, or dialed them so many times that they were eventually converted into long-term memory.

It is important to note that neither type of memory is perfect. This is why we forget things. In the case of long-term memory, when something is no longer significant, it may begin to fade. So if you move to a different house and get a new phone number, then you might forget your old phone number in a few months since you haven't used it recently. Long-term memory loss can also occur in old age.

Short-term memory loss usually occurs after a piece of information is no longer being reinforced by repetition or use. Also, most people can only store about 7 items at a time in their short-term memory, so "out with the old; in with the new" would be an appropriate way to look at it.

Little Lion Experiment:

Different people learn in different ways. Some are better at recalling images (visual learning), while others are more skilled at remembering sounds (auditory learning). Still others "remember by doing" (haptic learning). Almost everyone uses a combination of the above three methods, but most people lean more heavily towards one of them. To determine which of these memory categories best suits you, go here, scroll down a few paragraphs to the test section, and take the memory test. After you add up the totals for each of the three sections, you can figure out which type of memory you use the most (the higher the number, the more inclined you are to learn in that particular way).

What Is Special About The Octopus?

Eight arms, no ears, blue blood, rows of suction cups...this is beginning to sound like a science fiction movie, but in fact, we're talking about the octopus! Octopi (the word for more than one octopus) live in oceans all around the world but are generally found in warmer climates. They can range from 3/8 of an inch (the Californian octopus) to 23 feet (the Giant octopus)!

Octopi from different species (types) vary in appearance, but they share the same basic body layout: they have eight arms (each has two rows of suction cups), a head (with two large eyes, a mouth and a very advanced brain), and a mantle, which is the large soft sac attached to their head. Although the mantle hangs off of the head, it can be thought of as the torso of the octopus because it contains so many vital organs like the heart, a digestive system, and gills.

As you may know, an octopus uses the suctions cups (called "suckers") on its arms to grab onto prey, but they also allow the octopus to smell and taste its environment. Imagine if you could taste and smell whatever you held in your hands as soon as you picked it up...an octopus can!

An octopus can also be thought of as an aquatic chameleon because it can change the color of its skin. This is done to express emotion, or for camouflage (pronounced "CAM-o-flaj"), which means blending into its environment so it will be harder for a predator to see it. Octopi can also change the texture of their skin for camouflage purposes.

Scientists continue to discover new and exciting facts about octopi, but this is a difficult task since they tend to be rather shy creatures. In fact, an octopus spends most of its life in crevices, holes, and other hiding places. It does this in part to protect itself from predators.

If the octopus is attacked, it has a few defenses to save itself from being eaten. The mantle of an octopus produces ink (like a squid, which is a relative of the octopus). When threatened, the octopus squirts ink at the predator. This blocks the predator's view of the octopus as it escapes. In some cases, the ink also damages the predator's senses so it can't find the octopus as easily.

Like a squid, an octopus doesn't technically swim away; instead it moves by jet propulsion. It does this by squirting water behind it from an opening in its mantle. The force of the water leaving the mantle pushes the octopus forward. The octopus then takes in more water and repeats this process so that it sprints forward in starts and stops.

Octopi hunt by attaching some of their suckers to their prey (a crab, for example). They then use their beak to make a small hole in the shell of the prey. Afterwards, they inject a poison to kill and partially digest the animal before sucking it out to eat it. There are over 100 species of octopi but only a few are poisonous to humans.

Little Lion Experiment:

When a 3-pound octopus uses its suckers to grab onto its prey, it would take 40 pounds of force to pull the two animals apart! This amazing strength is due to the large number (about 2000) of suckers on an octopus, as well as the properties of suction cups.

When you push down on a suction cup, air is squeezed out, which creates a vacuum. The tiny amount of air left inside can't generate much outward force, but there is plenty of air outside to push inwards (this is called "atmospheric pressure"). This imbalance of the two forces is what makes it hard to pull a suction cup off of an object.

To explore this topic, obtain a small suction cup with a hook on the end (like the ones used to hang up pictures). Attach it to the bottom of a glass table or another very smooth surface [rough surfaces won't work since the texture will allow air to leak in]. Hang weights from the hook until the suction cup finally falls off. The total weight of all the things you hung from the hook equals the amount of force needed to separate that one suction cup. Now imagine having 2000 of those!

Why Do Your Ears Pop On An Airplane?

The human ear consists of the outer ear, your middle ear, and your inner ear which is fairly deep inside of your head. The middle ear is separated from the outer ear by the eardrum (or "tympanic membrane" in medical terms). So, the air trapped inside the middle ear doesn't come in contact with the air outside of your head. When you experience a change in air pressure by getting closer to or further from the ground, your ears will occasionally "pop" to adjust the pressure of the air that is caught in your middle ear so that it matches the air pressure outside of your head. This is done by quickly opening the Eustachian tubes (which connect the middle ear to the back of the nose) in order to let air rush in or out of the middle ear as needed.

The most common place for someone's ears to "pop" is on an airplane, but it can also happen with smaller changes in altitude (the height above the Earth's surface), like when you are driving up or down a mountain. The air closer to sea level is at a higher pressure since it is being compressed by the weight of all of the air above it. As you climb to higher and higher altitudes, the air pressure decreases.

Some people may find the popping of their ears to be annoying, but if your body didn't do this, then the pressure on one side of the eardrum would be higher than on the other side which could bend your eardrum slightly and compromise your hearing.

If your plane is taking off, then you are going to an area with lower pressure so the high-pressure air in your middle ear will push outwards on the eardrum. When your ears pop, air rushes out. If you are coming in for a landing, then you have low-pressure air in your head (from when you were at a high altitude) and high-pressure air outside pushing inwards on your eardrum. When your ears pop, air rushes in.

One way to make this pressure equalization more comfortable is to do it yourself by swallowing or yawning frequently rather than waiting for your ears to pop by themselves. These methods work because swallowing and yawning cause the Eustachian tubes to open briefly. This is why many people choose to chew gum when their plane is taking off or landing (chewing gum or sucking on a hard candy makes you swallow more than if your mouth were empty).

If someone has a blocked or oddly-shaped Eustachian tube, then their ear will fail to pop as their plane is landing. This creates a small vacuum in the middle ear. Fluid then rushes into the middle ear to increase the outward pressure until it equals the inward pressure from the surrounding high-pressure air.

Little Lion Experiment:

To see the effects of having a blocked Eustachian tube, obtain a small plastic cup and a bowl with a flat bottom. If possible, use a clear cup so the water will be easier to see. If you don't have a clear cup, then try adding food dye to the water in this experiment to it will be easier to see once it is inside of the cup. Fill the bowl with about an inch of water. Turn the empty plastic cup upside-down and squeeze it until it bends inwards. Place the bent cup in the water.

Being careful not to let the lip of the cup rise above the water level, slowly squeeze the creases in the cup outwards so that the cup returns to its original shape. By doing this, you are creating a small vacuum. So, the pressure inside the cup (which pushes outwards) is lower than the pressure outside of the cup (which pushes inwards), and this pressure difference is what pushes the water from the bowl into the cup until the two pressures are equalized.

As a side note, the same principles of air pressure explain how straws, turkey basters and a variety of other objects are able to move liquids against gravity.

How Can I Avoid Getting A Sunburn?

Have you ever forgotten to put on sunscreen, then regretted it the next day? Many of us know what sunburns look like, but do you know why we get them? Let's start with some background information on how our skin responds to light. Cells called melanocytes in the inner part of your skin produce the pigment melanin, which is what gives color to our skin. Believe it or not, we have about 1000 to over 2000 of these cells per square millimeter of skin! If you have dark skin, that means that your melanocytes are programmed to make a lot of melanin all the time. If you have lighter skin, then you have the same number of melanocytes, but they don't produce as much melanin. If you are albino, then your melanocytes cannot do their job because they are lacking an enzyme (a piece of cellular machinery) which is needed to make melanin.

On most days, we do not get exposed to enough sunlight to cause us to develop a suntan. However, a nice day spent at the beach is much different. The darker your skin is, the more light you can withstand without having to boost your melanin production. When your body senses that you need more melanin to protect you against harmful UV rays, your melanocytes kick into high gear and you get a suntan. However, if you stay outside for too long, especially without sunscreen, then your body can't make melanin fast enough to keep up with the amount of UV exposure. This is what causes a sunburn. A sunburn can be thought of as a "clean-up crew" of various blood cells being sent to repair the damaged area. This increased blood flow is what causes sunburns to appear red and feel warm to the touch. Starting to sound a bit like a sunburn? There's one thing missing: why does sunburned skin tend to peel? Your body does its best to repair the UV damage, but if the damage is too great, then the unrepaired cells will simply flake off to make room for new healthy cells to replace them, which allows the sunburn to heal.

You may have heard about the relationship between sunburns and skin cancer. Even though the "clean-up crew" and the skin cells themselves usually undo the harmful effects of UV, they may not always do a perfect job. This would allow damaged cells to stay in the skin. Most sunburns will not lead to cancer, but a tiny fraction of them can if they damage a cell's ability to stop dividing. This is why it is so important to wear sunscreen in order to avoid over-exposure to UV light.

There are two types of sunscreens: those that reflect UV light (like tiny mirrors) and those that absorb it like melanin does. Everyone gains extra protection from wearing sunscreen, but if you are fair-skinned or albino, it is especially important that you wear it. Remember to put it on around 30 minutes before you go outside so that it has time to stick to your skin. Otherwise, it will rub off on the grass or wash off in the water. [Safety note: some people (especially those with sensitive skin) have allergies to PABA, a chemical in some sunscreens. So if you have sensitive skin, you may want to consider buying a PABA-free sunscreen].

For more information, visit http://travel.howstuffworks.com/sunscreen.htm

Little Lion Experiment:

While UV light is harmful in some respects; we need it to stay healthy! This is because our bodies need about 10 to 15 minutes of daily UV exposure to make vitamin D. In fact, many reactions are activated by light (various kinds of light, not just UV). To see how important light is for living things to survive, obtain two small planter pots. Plant about 5 evenly-spaced seeds in each pot. If you cannot purchase seeds at your local hardware or gardening store, you could use seeds from a fresh tomato. Place one pot in front of a sunny window and place the other pot in a dark area (a cabinet would do, with your parents' permission). Remember to water the plants every few days (specific instructions can be found on the seed packet). Check on the plants over the next couple of weeks to compare the seedlings in the light versus those in the dark.