Congratulations to this months winning student submissions.

 

Section 1

Latisha “Snap” Lancaster

Faster Than A Speeding…Soundwave?

The Physics of Sound

 

By Tish Lancaster

 Have you ever wondered how sounds made their way to you? How do you hear a person speaking, a car beeping or a bird chirping? How does sound travel? Well lets find out!

Sound is made by the creation of vibrations that travel through the air. The vibrating body causes the medium (water, air, etc.) around it to vibrate. Traveling longitudinal waves are vibrations in air, which we can hear. Areas of respective high and low pressure called compressions and rarefactions make up sound waves.

 

Here is a traveling wave. The shaded bar signifies the varying pressure of the wave. Lighter areas are low pressure (rarefactions) and darker areas are high pressure (compressions). The indefinite repeating pattern called the wavelength is highlighted in red.

 

v = f • λ

The wavelength of voice is about one meter long. The wavelength and the speed of the wave determine the pitch, which is the frequency of the sound. The equation above shows the relationship between speed, frequency and wavelength (speed=frequency x wavelength). Sound travels at 343 meters per second (which is insanely fast!). Thus, frequency is determined by speed / wavelength. The longer the wavelength, the lower the pitch. The height of the wave is its amplitude. Amplitude determines how loud a sound will be. Greater amplitude means the sound will be louder.

Different sizes of wave compressions make for louder or softer sounds. A small compression makes a soft sound while a big compression makes a loud sound (like sonic booms). Again, Sound waves are longitudinal waves meaning they compress and vibrate in the same direction as they travel. Also, only the vibrations move, not the medium the waves hit or pass through. Vibrations occur via vibration of air particles, but the air itself does not travel. If sound waves are generated in the air they make a tone. To change the tone we would generate the sound waves at a different frequency. Higher frequencies make for higher pitched sounds.

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Fun Fact

Man has been able to beat the speed of sound with super sonic travel. Breaking this sound barrier produces both an audible and visible effect.

Check out this video of an F35 Sonic Boom.

 

 

In this photo you can see the effects on the air as the plane blasts through the sound barrier. This occurs because as the plane travels it pushes the air out of the way, creating pressure waves that travel at the speed of sound. As the plane approaches the sound barrier, the air can’t get out of he way quick enough and it is squashed together into one big shockwave that travels at the speed of sound. This pressure is not much greater than normal air pressure, but since it is released at such a speed, it’s audible as a sonic boom!

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So how do humans create sound?

Humans create vibrations in our pharynx. This is the area of the throat just above our windpipe, where our vocal cords are located.  More simply put, vocal cords are folds of tissue that vibrate when wind passes by them.

 

If you were to turn the throat on its side you would see how sound is produced.

When air from the lungs is forced across the vocal chords, vibrations occur. These vibrations squeeze the air creating areas of compression. These areas of air compression carry energy. The energy carrying compressions travel from place to place transmitting the energy. When they smash into an eardrum, they are heard as sound!

Here is a video demonstrating how the vocal cords produce sound. Notice how the difference in pitch affects the vibration of her vocal cords and how the vocal cord vibrations are faster than the human eye can pick up, so they look like paced, rhythmic waves.

So now you know how the physics of sound effect our lives everyday. Sound waves and vibrations are instrumental to our understanding of each other and the environment around us.

Using what you have just read, what do you thing would happen if one or both of our vocal cords were to enter a state of paralysis and cease to vibrate? (No Googling!)

(For Diigo sources click here.)

 

 

 

Section 2

Alexander “Alex” Henriquez

Hello class,

I honestly had no idea what to write about so I chose the first thing that normally comes to my mind when I think physics, rockets. While it may not be directly related to any formulas or numbers, I think they are neat and still relate to physics as a whole.

When you have an object moving through the air there are four basic forces that operate it; Lift, drag, gravity, and thrust.

Lift happens when the air above the object moves faster than the air below, causing less force against the top compared to below the object. You see this happen often in kites.

Drag is the force that rubs against the sides of an object as it moves upwards (friction). Smooth surfaces and streamlined designs reduce drag causing the object to fly higher.

Gravity is the force that pulls down while near Earth. It acts through the center of gravity of any object. This force’s strength is proportional to its mass and inversely proportional to the square of the distance between the object and our planet’s center.

The engine of the rocket produces thrust and is the forward force exerted on its body. Thrust must be more powerful than gravity in order for anything to rise vertically.

Newton’s three laws of motion also apply to the launch and flight of rockets, those being:

  1. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
  2. The relationship between an object’s mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector.
  3. For every action there is an equal and opposite reaction.

Keeping all these things in mind we can now move on to the fun part of this article, building a rocket! This isn’t going to be a model rocket or anything too complex, it is a water bottle rocket many of you can build right at home.

A few things to keep in mind:

  1. You will most likely get wet. Wear a poncho to protect yourself from water if you are afraid to get wet.
  2. While this rocket doesn’t have a real engine or anything too complicated the same principles stated above will work here.

With that said lets get to work. Some things you will need:

Water

Duct tape

Empty soda bottle

Bike pump

Paper (almost any kind will do)

Cardboard

Cork

You won’t need every item here; these are items I have used in the past to make a cool looking water bottle rocket. The absolutely essential items are the soda bottle, bike pump, and cork.

First you’re going to take the paper and roll it up into a cone shape. This is going to be the tip of the rocket and make it slightly more aerodynamic and reduce drag. Wrap the cone with the duct tape to make it more stable and water resistant. Attach the cone to the bottom of the empty bottle using more duct tape (the bottom of the bottle is the top of the rocket). Now you’ll want to cut the cardboard pieces into right triangles. These will be the fins for your rocket. You can attach them using some of the duct tape you have left over. Make sure you don’t cover the hole on the bottle (where the cap is normally screwed on). Fill the bottle up about 1/3 of the way with water. Now cut a very small hole through the center of the cork (not the sides) and very firmly push the cork into the bottom of the bottle. At this point if you’d like to build a stand or launch pad for the rocket (if you don’t chances are you’ll either make a mess or the rocket will fly towards a neighbor’s house) and set it up for launch. Attach the tiny needle-like valve of the bike pump into the hole you made in the cork and step back. Start pumping and get ready for launch!

The duct tape fins and rocket tip make the rocket smoother and will allow it to rise vertically easier. The less friction while rising the higher it will go, and although there is no complex engine, the force of the water shooting out from the bottom of the rocket should be more than enough to make the rocket rise continuously (until there is no more pressure inside the rocket).

Hope you had fun with this one (even if you only read though)!

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References:

Model rocket resource:

http://www.ohio4h.org/sites/d6-ohio4h.web/files/Designing%20Your%20Own%20Model%20Rocket.pd

Newton’s three laws:

http://csep10.phys.utk.edu/astr161/lect/history/newton3laws.html

 

 

 

Section 3

 

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