Sound is everywhere.  Music, birds singing, cars and people on the street, nearly everything around us makes some sound.   But what is sound really and how is it created?

Sound is created by moving or vibrating objects.  This vibration pushes and pulls on the air molecules close to the object, which then push and pull on the molecules next to them, which push and pull on the air molecules next to them, getting further and further from the object.  This phenomenon is called a longitudinal wave (a.k.a. compression wave).  A good way to visualize this is using a slinky: if you hold a slinky in mid air or lay it out on a table, and tap one end, the first coil of the slinky will push and pull on the second coil, which will push and pull on the third coil, and so on.  This causes a wave that moves all the way through the slinky, even though the slinky itself does not move. 

Here is a YouTube video showing the slinky demonstration, taken and uploaded by Trevor Murphy.  Thanks to Mr. Murphy for sharing this excellent demonstration!

When objects vibrate, they tend to do so at a certain frequency; that is, they move back and forth—or oscillate—at a certain speed.  This pushes and pulls on the air at a particular speed, causing the wave generated to have a certain sound.  This is how a tuning fork works.  A tuning fork is a two pronged, U-shaped fork that vibrates with a certain frequency (and therefore a certain sound) when struck.  They produce a very consistent sound corresponding to a certain note, and thus are used by piano tuners to make sure the instrument is producing the right notes. 

Just like a tuning fork, U-shaped glasses made of thin glass also tend to vibrate at a certain frequency, depending on whether they contain any liquid.  A wine glass is an excellent example; tap a wine glass gently with your finger, and it will usually produce a ringing sound.  This is caused by the vibration of the glass, and corresponds to a certain note just like the tuning fork.  In fact, if you play this note at the wine glass loudly enough, the glass will vibrate so hard it will shatter!  Here is another YouTube video demonstrating this phenomenon, which we don’t recommend you try at home! 

Thanks to Harvard Natural Sciences Lecture Demonstrations for producing and uploading this video!

While you shouldn’t try to shatter glass at home, there is another way you can experience the vibration of a wine glass using your finger and a little water.  This will cause the glass to oscillate at a particular frequency, creating a certain note. 

TRY IT!!

Here’s what you’ll need:

1.       A stemmed wine glass, the thinner the glass is the better.

2.       A small amount of water (just enough to get your fingers wet)

Here’s what you need to do:

1.       Set the wine glass on a flat surface.  Hold the very bottom of the stem to keep the glass still.

2.       Wet your fingers well.  This allows your fingers to glide along the rim of the glass easily.

3.       Slowly start running your fingers around the rim of the glass, using the part of your finger between the tip and the second knuckle.

You may have to practice a little before the wine glass begins to make sound.  Keep trying!

CHALLENGE YOURSELF!

How many notes can you make with your wine glasses?  If you add water to the glasses, they will create a different note when you run your finger over the rim, depending on how much water you add.  See if you can create a whole scale or play a song!  With a lot of practice, you will eventually be able to play like Robert Tiso, who in the video below plays Dance of the Sugar Plum Fairy by Tchaikovsky using only glasses and water!  Thanks to Robert Tiso for sharing this amazing video—ENJOY!

In nearly every household around the world, it is not unusual to go to the cupboard now and then and see a sight like this one:

Most people are a little disgusted when they see this, some are fascinated, and virtually nobody finds it appetizing!  But what exactly is it?

The fuzzy green carpet that appears to be covering your bread, fruit, or vegetables when they’ve been around just a bit too long is called mold.  Molds are a type of fungus, a microorganism—that is, a tiny living thing—made up of multiple cells growing in long strands called hyphae.  The fuzzy mass that the hyphae create is called the mycelium.

Molds may not be very appetizing—you should throw away food that you see is growing mold—but they are very important!  They perform very important functions as decomposers of litter, in production of some of our food, and even in medicine! 

Molds as Decomposers

As living things are born, grow, and eventually die, something must happen to the waste produced by these living things, as well as to their bodies when they die.  Molds are partially responsible for the breakdown and digestion of this litter, and so they facilitate the return of the nutrients contained within these living things back to the soil.  If molds and other microorganisms could not do this, the nutrients contained in the bodies of dead plants and animals would remain there forever, and the soil would never get them back, making it impossible for new plants to grow, and new animals to be fed.

Molds in food production

Molds are traditionally used in the production of a variety of different foods, such as soy sauce, cheese, and salami.  The molds break down the sugars and starches of the soy and milk, allowing them to ferment (a process which turns sugars into acids, alcohols, and gasses), which improves the nutrition, flavor, and/or shelf life.

Molds making medicines

One of the most important discoveries of the 20th century was the discovery of penicillin, one of the first antibiotic drugs to be used widely, and which was of great importance during World War II (see Reference 3 for more information).  Penicillin is produced by a group of molds called Penicillium, and is still used today. 

Another medicine that is produced by molds includes the immune suppressing drug called cyclosporine, which is used to prevent patients’ bodies from rejecting newly transplanted organs (like lungs or hearts).  Cyclosporine is produced by the mold Tolypocladium inflatum, originally found in Norwegian soil.  Several cholesterol lowering drugs are also made by molds. 

While most molds are not dangerous to the average person, if enough mold is present in the surroundings it can make you sick.  There are also some types of mold that are extremely dangerous, producing toxic compounds that can cause nerve damage and even death.  These are not present everywhere, but it is always best to be safe, and avoid exposure to homes or other buildings with lots of mold growth. 

GROW A PET MOLD!

Here’s what you’ll need:

1.       A piece of bread, preferably homemade or from a local bakery

2.       A zip top bag

3.       A pair of scissors

4.       A warm, dark cupboard that is NOT used to store food

Here’s what you need to do:

1.       Place your piece of bread inside the zip top bag, and close it carefully

2.       Cut a few very small slits in the bag to allow air circulation

3.       Place the bag in the cupboard, and make sure no one eats the bread!

4.       Allow the bread to rest undisturbed for at least a few days, then up to a few weeks, checking it daily. 

What did the bread look like after two or three days?  After one week?  After two weeks?  Write down everything you observe in your journal, and take pictures of the bread every few days if you can; pictures are a great way to record changes!

References for further reading:

1.       “Mold.”  Wikipedia.  September 12, 2014.  Viewed on 9/16/14.  http://en.wikipedia.org/wiki/Mold#Pharmaceuticals_from_molds

2.       Campbell, N.A.; Reece, J. B.; Mitchell, L. G.  Biology, 5th ed (1999). Addison Wesley Longman, Inc.  Menlo Park, CA. 

3.       “Penicillin.”  Wikipedia.  September 16, 2014.  Viewed on 9/16/14.   http://en.wikipedia.org/wiki/Penicillin#History

4.       “Tolypocladium inflatum.”  Wikipedia.  July 29, 2014.  Viewed on 9/16/14.  http://en.wikipedia.org/wiki/Tolypocladium_inflatum



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We see air planes nearly every day, flying in and out of airports, leaving vapor trails across the sky.  How can such a large, heavy object fly?  After all, even the smallest of air planes is over 1500 pounds!  We can find the answer in something called Bernoulli’s principle.

To fully understand Bernoulli’s principle, we first have to understand air pressure.  There is air all around us all the time, and this air is always pressing on us.  Because the air is pressing on us evenly from all directions, we usually don’t notice it. 

When objects move through the air they must push it out of the way,  just as they would if they were traveling though a liquid or a solid.  As it is pushed out of the way by the object, the air moving around the object must move faster than the rest of the surrounding air.  Think of it this way:  imagine a shallow swimming pool full of ping pong balls.  If you run from one end of this pool to the other end through the ping pong balls, the balls you push out of the way as you run will need to move faster than the balls farther away from you.  This is exactly what happens to the air as an object moves through it—the air molecules are like the ping pong balls, being pushed out of the way! 

As the air molecules move faster, they are not able to exert as much air pressure—and this is where Bernoulli’s principle comes in.  Bernoulli’s principle states that an increase in the speed of a fluid (either a liquid or a gas) is accompanied by a decrease in pressure.  Therefore, as this fluid moves from an area of high pressure to an area of low pressure, it will speed up—this is why when the atmospheric pressure drops, the wind begins to blow! 

This also means that as fluid moves faster, its pressure—that is, the amount of force with which it pushes against other things—drops.  This effect is the reason why airplanes can fly.  To understand this, we need to look closer at an airplane’s wings.

The wings of an airplane have a very particular shape:  the top of the wing is more curved than the bottom of the wing.  Because of this extra curve on top, the air flowing around the wing has farther to travel around the top of the wing than the bottom of the wing.  This extra distance means the air travels faster, reducing the pressure over the top of the wing.  The reduced pressure on top of the wing allows the pressure on the bottom of the wing to push the airplane upward, causing it to fly!

TRY IT!

You can demonstrate Bernoulli’s principle for  yourself with a very simple experiment.  All you need is a sheet of paper (at least 5 inches wide and 8 inches long), and some clear tape!

Here’s what to do:

1.       Take your sheet of paper, and fold it along its width.  The fold should be about one inch off the middle of the sheet.

2.       Bring the edges of the paper together, and hold them in place.  Use your tape to tape the edges together.

3.       Blow across the edges of the paper, and observe what happens!

What happened when you blew across the paper?  Did it move?  If so, which way?  Be sure to write down all your observations!


References for further reading:

1)      Lord, M.  “Lesson: Get a Lift!”.   eGFI.  March 25, 2011.  teachers.egfi-k12.org/get-a-lift/

We know living things are made of cells, and that nearly all living things are about 70% water.  But how does a living thing absorb water?  Each cell of a living organism is completely enclosed by the cell membrane...how can water get in and out?

The answer is osmosis!  Osmosis is the passing of a solvent (usually water) through a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration, generally until the solute concentrations on both sides of the membrane are approximately equal.  To understand this fully, we must understand both what solvents and solutes are, and what semi-permeability means.

A solvent is a substance, usually a liquid, in which solutes may be dissolved.  In the case of cells, this is water.  Other common solvents you may be familiar with include alcohol, acetone (commonly found in nail polish remover), and even air—remember gasses can be solutes also!

A solute is any substance dissolved in a solvent.  In a cell there are many solutes, such as salts, sugars, and other small molecules.  Simply put, a solute is the substance that is dissolved, and the solvent is the substance that does the dissolving.

A semi-permeable membrane is a thin, selective barrier that only allows certain things to pass through it, while keeping other things on one side or the other.  We see semi-permeable membranes very frequently in biology—nearly every living thing has them not only as the outer membrane of their cells, but also as part of the organelles within their cells.  These biological membranes allow water to pass through, without allowing most solutes to pass. 

A very good example of osmosis in action is what happens when we put red blood cells into solutions with different amounts of solute.  These different solutions may have more solute (hypertonic), less solute (hypotonic), or equal amounts of solute (isotonic) as compared to the red blood cells. 

Put the red blood cells in a hypertonic solution, and water will flow through the membrane out of the cells, since there is a higher solute concentration on the outside of the cells.  As a result, the cells will become wrinkled and shriveled up!

Put the cells in a hypotonic solution, and water will flow through the membrane into the cells, since there is now a higher solute concentration on the inside of the cells.  As a result, the cells will become very full and bulge, and may even burst!

If we put the cells in an isotonic solution, the solute concentration is now balanced between the inside and the outside of the cells, allowing them to maintain their normal shape. 

TRY THIS!

A good model of a cell is a typical chicken egg—it has a shell on the outside, but remove that hard shell and it also has a semi-permeable membrane on the outside! 

After you remove the shell using vinegar, you can do some pretty interesting things with your egg!

Here’s what you’ll need:

1.       Two eggs (extras are appropriate, just in case!)

2.       Two cups of vinegar

3.       One 3-4 cup clear plastic cup or bowl

4.       One large slotted spoon

5.       Two small, wide mouthed drinking glasses

6.       One cup of pure distilled water

7.       One cup of corn syrup


NOTE:  This experiment requires some planning ahead; preparing the eggs will take 24 to 48 hours.

Here’s what to do:

1.       Place your eggs in the clear plastic cup.

2.       Pour the vinegar over the top of the eggs.

3.       Wait 24-48 hours for the vinegar to dissolve the egg shells!  Look closely at the shells as they are dissolving in the vinegar—you should see small bubbles forming on the shell.

4.       When the egg shells are fully dissolved, carefully remove them from the vinegar with the slotted spoon.  Place one egg in each of the two drinking glasses.

5.       Pour one cup of corn syrup over one of the eggs.

6.       Pour one cup of distilled water over the other egg.

7.       Allow the eggs to sit at room temperature for 3 hours to overnight.

8.       Remove the eggs from their glasses with the slotted spoon, and place them carefully on the table.

What do the eggs look like?  Has their appearance changed?  If so, how?  Based on this observation, which of these solutions is hypertonic?  Hypotonic?  Sketch the way the eggs look, and be sure to write down all your observations!



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