High Above the Chimney Tops

For this journal I pulled a Mr. K and attempted to take a picture of this rainbow with my iPhone while driving along the Ala Wai this weekend, which is a little harder driving manual. This rainbow is created by the total internal reflection of light inside individual raindrops, in which the angle of incidence of light inside the raindrop creates an angle of refraction that is 90 degrees or greater (the critical angle), and thus light does not exit the raindrop, but bends back in the other direction and exits a different way. For us to percieve rainbows, we require that the sun is behind us (it isnt visible in this picture, so that is fulfilled) and the raindrops are in front of us (also not visible in this picture), so that the light will reflect into our eyes. An important part of seeing all the colors of the rainbow is dispersion, which is refraction that causes light to seperate into its various wavelengths. Since white light is made up of red green and blue, which subsequently make up all the colors, all with varying wavelengths, each experiences a slightly different change in speed and wavelength when entering and exiting the raindrop, and thus we see them stacked upon each other. Since different wavelengths are variously refracted, we only percieve a single color refracted from a single raindrop, and thus our image of the rainbow is made up of the refracted light from many different raindrops.

Doppler Effect

So, while this isn't the best physics journal photo i've ever taken I think it clearly shows the true spark of realization of physics concepts in the real world (especially the bluriness and off-center-ness). So when walking around this weekend I experienced the Doppler Effect via this fire engine's movement and siren/horn. The Doppler Effect is the percieved change in frequency of a sound wave due to movement of the source of the sound or the one listening to it in relation to the source. As the fire engine sped toward me there was a build up of sound waves as it continued to get closer, resulting in a percieved higher pitch, yet the siren and horn are only single pitchs. Once the fire engine passed me and proceeded away from me, the listener, the sound waves reached me in longer intervals, which made me percieve a lower frequency, and thus lower pitch. If my iPhone somehow could have recorded the speed of the fire engine and the frequency of its siren while I took the picture and I could assume my speed, it would be possible to determine the frequency I percieved through the equation: fn=f((v+/-vL)/(v-/+vS)), where v is the speed of sound. This equation states that while the listener moves closer to the source or the source moves toward the listener the percieved frequency is higher, whereas when the listener is moving away from the source and vice versa the percieved frequency is lower.

Wave Motion Gun

Even though the title and the picture (the effect in the picture is based off the same concept as this journal though! [i think]) kind of suggest something, i'm not referring to illicit items, but the physics involved in my electric guitar. After learning about waves in our latest lesson, i began to notice the transverse waves created when i plucked my strings in stage band, which consequently produces longitudinal waves of sound that travel through the air and the floor and to our ears for interpretation. Sound and light are types of mechanical waves, and thus involve this force and said mediums to travel though. These waves cause particles to move back and forth, which allows the transfer of energy. Waves are measured in several different ways, all of which i found are important to my playing. The amplitude of a wave measures the height of the crest to the equilibrium and is percieved as the volume, as it increases so does the volume. The wavelength of a wave is the length of one cycle in meters, and as it decreases the frequency, or number of cycles per second, increases since they are inversely proportional. Thus, when i fret higher frets on the guitar, i am shortening the wavelength and thus increasing the frequency, which raises the pitch as we percieve it. Electric guitars have an added depth of physics, and their sound is made possible through electromagnetic induction, which uses the magnets in the pickups and the change in flux caused by plucking the strings, which disturbs the magnetic field to induce a current, which is sent to the amplifier, thru which the signal is magnified to produce "one big blast from your wave motion gun," although in a different context.

Extra Credit

Rock and Roll Ain't Noise Pollution

This week's physics zen came courtesy of my car audio. When i was taking my friend home he thought it'd be fun to crank up the volume on my alpine deck to 18 (i listen to it at 7 usually) at 11:30 PM. After worrying that it would blow out my speakers because my amp is rated at 3000 watts, i remembered physics and, thanks to class, remembered how all that power was generated: capacitors.
Capacitors are like batteries in the sense that they are able to store energy. Unlike batteries however, capacitors are formed by two conducting plates that can hold equal but opposite amounts of charge, separated by a good insulator, which can be released instantly when the plates are put into contact. While they are not able to hold as much the fact that they can release all of their energy instantly and be recharged makes them very useful for car audio, which requires lots of power at volume 18 in my car. To charge a capacitor, a power source such as a battery moves the charge off one plate and adds it to the other until both have the same voltage difference. The ratio of charge on one of the plates to the overall voltage difference is called Capacitance, measured in Farads. Capacitance can be increased with the presence of a good dielectric, which reduces the field strength between the plates to allow more charge to be separated and thus discharged. After being discharged the voltage difference returns to 0 and can be charged again infinately.

Punahou Carnival Physics

Last weekend, while walking around the Punahou Carnival I had the strongest physics realization all year: All these rides are possible because of what we've learned in physics!!! Whipping out my iPhone, I began to take pictures of all the rides with the Snapture app (not on the app store) while fighting my way through the crowd. After getting home from a great carnival and reviewing my majorly blurry pics i stumbled upon this one which turned out surprisingly well. One of my favorite rides when I was little, the swings serve as a great example of rotation, angular velociy and acceleration, and centripetal force. As opposed to picking up speed tangentially, which is hard to measure since the direction of each rider is constantly changing, one could theoretically measure the angular velocity of the riders during the ride and the angular acceleration/deceleration as it starts and stops by measuring the change in the angle per second, and the rate at which that increases or decreases. Additionally, since this does experience angular acceleration it is safe to assume that something within the ride provides torque, or a force that causes an object to rotate. Lastly, since the swings are travelling in a circular motion, the riders are experiencing centripetal force, a force that varies in form (in this case the horizontal component of the tension in the chains that lead from each swing to the top) and causes the riders to travel in a circular motion until the centripetal force is overcome, in such case the riders would exit the circular motion tangent to the point where the force overcame the centripetal force, which fortunately didnt happen.

Tuning Physics

This weekend I got a call from my friend with a Toyota Celica who wanted to install a new pair of Eibach ProKit springs (very, very jealous). Since i did not think about the physics opportunities and was not aware a journal was due tonight (we did one last week mr k!) i never took a camera, and upon realizing it i took a snapshot of two pages of my January/February issue of Project Car, the very issue we used for directions for the 3 hour project. Naturally, the physics in the project came in the form of torque. However, this torque was not applied by the car as one might expect (sorry mr k, i kept bugging my friend to open the engine up so i could see the cams and where the real torque is generated but he wouldnt budge), but instead by our hands and tools as we removed the old crusty springs and struts and put in some brand new ones. First off, we used a spring compressor, which applies tangential force to the spring in order to compress it so it can be fit into the upper mount. To replace the old, crusted nuts we used WD-40 and a wrench, a perfect example of torque. Sometimes, when it was just too rusted over, I improve my torque through three different methods: pulled perpendicularly, extended my lever arm (the pipe trick works well on the larger ones) and by adding more force (ie calling my friend over to do it). We also used specialized tools that displayed properties of torque, such as an impact gun, which can spin the upper nut fast enough so the strut won't spin, and a torque wrench which let us apply the factory recommended specs by controlling specific measurements of rotational force. In addition, we swapped his rims from the factory steelies to forged ones, which help to provide a more ideal moment of inertia. As opposed to the heavy, concentrated factory rims, forged rims are lighter, stronger, and have a more ideal weight distribution which results in a faster and more appealing ride.