Gravitational Potential Energy: An Episode from the Past!

Today, I made some new friends at Richard's house. And I just love introducing new friends to people! But I don't have names for them (yet).

For the last couple of weeks during our study of electrostatics, a key to many problems is calculating electric potential and electric potential energy (there IS a distinction between the two!). Conceptually, doc! used the model of gravitational potential energy to help explain electric potential, as the two are actually quite similar.

While finding homes for my new friends, I discovered that some habitats were at greater heights than others. Since gravitational potential energy equals mass times acceleration due to gravity times height, the habitats located higher on the storage bin should have a greater potential energy, right?

To take a page from the writers of the AP Physics B book, this blog will have a "Gotchas" section (which doc! never makes us read, but it's fun to, anyway). Because I forgot to mass each of my friends and measure the actual heights of each level of the storage bin, calculating gravitational potential energy is impossible. Ranking the gravitational potential energies is hence, also impossible.

While usually a higher elevation results in a greater potential energy, we cannot assume that the highest potential energy habitat is at the very top without making our own hypotheses about the masses and heights of Hamtaro, Dog, and Bear. For example, Hamtaro is the highest, but probably has the lowest mass. M will be a smaller value than for the other friends, but H will be a larger value. The same dilemma holds for dog and bear; we can only generalize about whether M and H are greater or lesser in correlation with the other friends.

The only thing we can say for sure, is that the potential energy of Mr. Killer Whale is zero, because he is at a height of zero: mass times acceleration of gravity times zero equals zero, regardless of what the other numbers are.

Insulators

Electricity, indeed, is an abstract topic; to read about, understand, and especially blog about. Physics has definitely gotten more challenging, "kicked up a notch," and the added time pressure on tests isn't too helpful, either. But I can't help but feel exicted, too. One more semester from junior year, and i'm done forever. wheeeeee!

Recall from last week that an insulator resists the flow of energy, most commonly either heat or electrical. However, the American Heritage Dictionary also defines an 'insulator' as more generally, something that segregates from and/or prevents from happening. Am I allowed to say that this blog is 'insulating' me from doing my APUSH research proposal? Someone tell me!

In general, insulators and conductors are dichotomous--any object is either one or the other. Just like conductors, an average household is filled with insulators! Here's some that I believe every household should have:

wood (paper is made from wood, sort of)


glass


rubber (so then, what happens when you flip an electric switch with wet, rubber gloves on? someone try and let me know the results)*


now, onto the six pages of my research proposal, which is going to be twice as long as the actual paper itself. see you next week, yo!

* (asterisk denotes that author reserves the right to clarify and will not be subject to any incidents of pain and suffering and/or will not be liable for any accidents that may occur)

Conductors

It's really kind of annoying when the physics test that everyone thought was easy, in (including yourself), in fact, so easy that doc decides to pull off the curve, turns out to be your worst test in second quarter, actually perhaps in the whole year. /sigh; oh well!

In class, we've moved from thermodynamics to electricity, which means a bunch of new stuff, and hopefully (for me) a better test. I did notice that just like how there are thermal conductors, there are electrical conductors. The same, of course, goes for insulators.

In both cases, an insulator resists the flow of energy, either heat or electrical energy. A conductor, then, allows the transfer of energy. This week's focus is on a couple things I could find in my house that are appropriate conductors of heat and electricity (there are a lot more than I thought!).


the wiring system which hooks up my router/road runner
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no idea why that bandaid was there..

so why are cooking things made out of metal? you tell me!

Some observations:

-any kind of metal is a good conductor.
-any kind of wiring is extremely good, too.
-water is a great electrical conductor but a terrible heat conductor. hmmmm....

With this, we know why parents always nag about drying your hands before turning off the light switch in the bathroom. See you next week for insulators.

Thoughts on Finals, Does anyone use CDs anymore? The Future of Google in China?

January 17, 2010

A few blogs into the New Year. Feeling pretty good. Finals are over. APUSH is over, which effectively doubles my free time.
Hell yeah!

We should all take some time to thank Doc, the heavens, and whoever else lent a hand in eliminating the semester AP Physics B exam. I literally got under two hours of sleep on some nights, which is just not fun. An additional exam, especially physics, might just have made me want to kill myself just the same, but a lot more.

I always try my best to give credit where it is due. This week, that means putting my trusty Sansa MP3 in the spotlight, for being my best friend in these times of crises, and getting me through it all. This being, of course, the same one I got for Christmas and generally carry EVERYWHERE:



Of course, I need to keep my 'best friend' updated with the latest music and sound clips. Most of the time, I get the music burned on a CD and download it to my computer, from which I can transfer directly to the Sansa. Takes less than 30 seconds to upload the entire CD!

But I guess the irony of it all, in this day and age, is that CDs have gone through Napoleon status: from towering heights of popularity to completely obsolete. The CDs I use were all ones that I had from before, but never listened to, because, well, they were CDs. Last Thursday, my friend sent me a playlist from a Rise Against album which I just couldn't resist picking up. I decided, then, to take a blast into the past (cliche much!) and burn it on a CD, and listen to it that way, for nostalgia's sake. I had to borrow my dad's coworker's CD player to use it, though, since really, who the hell uses CDs anymore? (did I say this already?) I forgot to grab an actual picture, but it looks something like this:



I noticed that after the initial time it took for the CD to get going, it spun around on the player in uniform circular motion, just like we studied in November. The radius of a standard CD is 6.05 cm, or 0.0605m, and the mass of a standard CD is 14.4g or 0.0144 kg. Knowing these two meaningless facts, we can find a lot more meaningless things!

A Review on Rotation formulae:
Radial/Centripetal acceleration is equal to velocity squared divided by radius. Since Newton discovered that Force equals mass times acceleration, Centripetal force equals mass times velocity squared, all divided by the radius.

Furthermore, if I calculated the period of one rotation, I could calculate tangential and angular acceleration, too. This can be done with the formula, Tangential Velocity equals (2pi)(radius)/(period). Angular acceleration equals simply (2pi)/(period).

We also did a chapter on rotational kinematics/dynamics and studied about angular velocity, angular acceleration, and angular displacement. Given angular velocity, we can figure out so many more meaningless things about my CD on a CD player.

Now, I'm not going to calculate all of those things, because it is 12:31 A.M., but feel free to do it if you want to! I'm off to do my problem set, which looks inherently difficult. . .

In other news, Google has gone down the tubes in China, I guess. Baidu stock at an all time high, as of 8 hours ago!

Who Really Cares about Sleep, The Internal Energy of Compressed Air

This Thursday and Friday are finals. Tonight's the last weekend night I'll have to study for them. Oh my god!

Sleep has been really tough on me, I guess. But more or less, I've gotten used to it. I no longer need to panic when I still have a million things to do, and it's ten or eleven P.M. And my parents, my loving parents, do tend to understand. They don't really bother me anymore, understanding that Iolani is really unforgiving as far as homework goes. And me, sinister ol' me, still spends substantial amounts of time while 'doing homework' talking to friends and not being productive. Food for next year's New Year's Resolutions, I guess.

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Today is Sunday, and I decided to crack open my desktop PC (literally) to clean the inside. I went to Walmart and bought a can of compressed air to remove damage-causing dusts and lints in inaccessible areas. The last time I did this was years ago, so the dust buildup was tremendous. I had to use the entire can! With 20% more! (thanks, Walmart)

Towards the end of the can's life, I noticed that it got extremely cold to the touch. I thought about it, and initially assumed that it was an application of the Ideal Gas Law. Since pressing the valve and releasing air reduced overall pressure in the can of compressed air, temperature should consequently decrease, because pressure and temperature are proportional:

PV = nRT (can)

R and n remain constant. Hence, PV = T; Pressure and Volume are directly proportional to Temperature.

Fair enough. But then, I read the fine print on my CleanSafe can, which indicated that less than 5% of the product was actually gas; the name "compressed air" is misleading in that most of the product (the other 95%) is actually stored as a liquid at an extremely low temperature. What we need is an equation that applies to both gases and liquids.

Upon doing some further research, the answer appears to be the Joule-Thomson effect, something we haven't learned yet. But here's the Wikipedia definition:

"In thermodynamics, the Joule–Thomson effect or Joule–Kelvin effect or Kelvin–Joule effect describes the temperature change of a gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment.[1][2][3] This procedure is called a throttling process or Joule–Thomson process.[4] At room temperature, all gases except hydrogen, helium and neon cool upon expansion by the Joule–Thomson process.[5][6]"

I'm not going to publish this as some sort of discovery, because I don't expect to be right on the money. In fact, I may be completely off the mark. But here's my interpretation of it (in English!)


Fluid exits the valves and is accelerated. Since energy is conserved, the additional KE must come from somewhere. "Somewhere" is the internal energy of the gas. Internal energy is directly related to temperature, as we've learned in class.

Hence, the accelerated gas will have a lower internal energy than the canister gas and will therefore have a lower temperature. That's why upon usage of the can, compressed air eventually feels extremely cold.

I feel like a SCIENTIST! (Someone tell me, please, if I'm completely wrong, so I can change this blog)



plus, I look kind of creepy. especially if you enlarge the photo :[

Violining, part two!

Four more days, guys. Just four more days. Hang in there, don't stress, and most importantly, keep up!




With that said, recall from last week how the tensions of both the bow and strings of a violin contribute to its sound. The tuning pegs or the bow's screw need to be adjusted precisely and carefully to produce the optimal sound. Now that the mechanics have been explained (somewhat...), we can move on to the finer aspects of violin: the sound itself!




We've learned in physics that a "repetitive vibration" causes a continuous, periodic, sinusoidal-shaped graph. But if violinists played with a "repetitive vibration," they would be limited to the same note, at the same pitch, with the same frequency. That would be boring! Much more often, we enjoy listening to varied notes, varying (or at least extremely quick) speeds, at different pitches. Here's David Garrett breaking the violin speed record!




There are other aesthetically pleasing things violinists can do to dazzle audiences, too. Vibrato is a vibration in the left hand that causes a pulsating change in pitch. It adds character to sound as opposed to just a flat note. A tremolo is the same concept, except with intentionally a much higher frequency to produce a "trembling" effect. Both take time and skill to develop, but are essential tools to violinists. Without these dramatic variations in frequency and pitch, violinists simply don't sound good, and consequently they wouldn't be successful in getting our money. Most importantly, though, we would lose doc! as one of the people who show up to Orchestra 5 concerts. People like Mozart and Bach and Beethoven would be nobodies. Many violin-makers would lose their jobs. The economy would thus undergo a huge recession. The stock market might explode and the world could end in 2012.


And so I end today with a fun fact: recall that a sound that is ten times as intense is only perceived by humans to be twice as loud. Essentially, a violinist needs to work ten times as hard for you to hear only a two-fold increase in volume. And the reverse must be true too: a violinist needs to work ten times as hard for you to sense a two-fold decrease in volume. Appreciate what we do for you, guys!

The Physics of Violin

The result of a very short weekend and some very substantial writer's block is this week's feature on my very good friend, the violin.

Before reading about harmonic motion and some introductory remarks on sound, it had never occurred to me that music was all about physics. And by next week, we'll know even more about sound. Well then! ....um, I'll cover that next time. Soooooo!

Since sixth grade, when I first picked up a violin, I had messed around with things like tension and friction to get a desirable sound. Granted, I probably used the wrong word there; calling it "desirable" would be extremely misleading. Oh well, as usual, it's Sunday night!

At any concert featuring any string player, the first and foremost requirement is properly tuned strings. A violin's four strings are affixed to four tuning pegs, which when turned clockwise, increases the tension on the string. Consequently, this increases the frequency of the sound produced by the string (the sound's pitch is "higher.") The opposite, of course, results when a violin is tuned counterclockwise. Since so many different tensions can be achieved with the tuning peg, strings can be tuned to whatever note is desired. On the same end, however, tuning is sometimes a difficult and frustrating task. Back when I really was clueless about tuning, I recall breaking a few strings when I increased the tension too much.




Aside from a properly tuned instrument, a violinist's bow must be appropriately groomed with sticky substance, and lots of it. Conventionally, the bow is made with horse hair and coated with rosin. Without rosin to increase the coefficient of friction on the bow, the sound produced is very weak or completely nonexistent. Using too much rosin, of course, results in a very harsh, sticky sound. Another amateur mistake I probably made in sixth grade.






Moreover, the force of tension applies for the bow, too. Turning the screw on the bow (clockwise) increases the tension on the hair. Just like the strings, the hair needs just the right tension to produce the optimal sound. Careful owners of bows always say to loosen the hair completely after playing, each and every time. I say forget it. I generally remember this only after putting my instrument away, zipping it up, and closing the buckle. At which point I refuse to unzip my case, unbuckle my buckle, and take my bow out again, because I just can't be bothered to do all that. How annoying.

And so with a properly tuned instrument, a properly tightened and rosin'd (yes, I make up cool words) bow, a good violinist can start playing and dazzling audiences. Well, not exactly. You can play with an untuned instrument, with an un-tightened bow, without any rosin. You'll survive. I did.