# willorn

Members

55

2

## Blog Entries posted by willorn

I can already tell this post will have a lot less structure than usual.

I've been thinking about special relativity quite a bit more than usual these past few days, in particular, the twins paradox. We didn't discuss it, but it seems to me that the actual aging is not the paradox involved, but the question of which twin aged how much is the paradox, since the earth twin would believe the other twin to be 40 years older and the space twin would think himself only 4 years older. Secondly, we discussed that special relativity applied to objects either in constant motion or at rest. In other words, objects in an inertial frame of reference.

That being said, the brother traveling in the spaceship must have experienced some sort of acceleration throughout his journey, when he left earth for example, and most likely when he turned around and when returned to earth. Therefore, I do not even think that the laws of special relativity apply to this situation. The question then for me is in that situation what would happen?

I imagine that the twin on earth has aged physically by forty years and that the twin who traveled has aged physically by just four years, and that no paradox exists at all.

Something else I have been thinking about: E=MC^2
I never truly understood the principle, so I looked online for the experiment used to determine this formula, and then attempted to derive it myself. I found that a useful experiment to reference (although theoretical) is this: a box is stationary in a vaccuum. A photon moves through the box from left to right. Since a photon technically has momentum, the box must then move left in order to conserve momentum of the system. When the photon reaches the right side of the box, the impact causes the box to stop moving.

However, since no external forces acted on the box, its center of mass must be in the same position as before (new concept for me!) but the box has moved left. Therefore, Einstein determined the photon must have a mass equivalent in order to satisfy the laws of physics.

I dreged up an equatin devised by Einstien to get started. I wonder if he came up with this expression before or after he determined that E=mC^2, because that would make this post seem rather silly. Since, a photon is massless, I was able to draw a simpler conclusion from his equation.The momentum rho is the momentum of both the box and the photon, by conservation of momentum.

Running low on ideas, I nosed around some more, and found that I should start thinking about the time it takes the photon to move from side to side. That train of thought led me to the following. The key is that velocity is change in displacement over time and that the time the photon required to cross the box is the length of the box side over the photon's velocity.

Thanks to what I learned this year in class, I know the center of mass of a system can be expressed the sums of products of mass and displacement of all individual parts over the sum of all individual masses.
I determined that if the center of mass did not move, then the position of the center of mass must have been in the same position as the box after the system resolves itself.

We can substitute X2 (the displacement of the photon) to be L the length of the box because it traveled the full length of the box.

Reviving the previous equation created and substituting it for m(delta x):
(I can do this because although the expression reads differently, the displacement after represents the displacement of the photon after colliding with the box's side, and the Mass is of the same object in both cases)

I find that deriving an equation always helps me to conceptualize it, and I hope this derivation helps you too! In my probing I also discovered that all mass has a measurable frequency, although it has little or no effect on people. More on that later...
Since there's nothing better than rolling spheres and sliding blocks in physics, I figured my first blog post ought to be about one or both of the two. Unfortunately, I can't think of anything with sliding blocks that hasn't already been done, so this post will be about spheres.

The Question I'm trying to answer will be: "If we are supplied with given information about a billiards player's first shot in the game (the "Break") can we determine the resulting force on the two corner billiards balls using momentum and impulse? Assuming that the Triangle Rack is set up perfectly.

Let's just say that the average pool shark can imbue his 160 gram cue ball with 20 Newtons of Force in .05 seconds. Billiard Balls are made of Phenolic Resin Plastic, which has a notoriously low coefficient of friction. Take into account the soft cloth table, and the fact that the slipperiest solid we know of has a coefficient of .02, and we can reasonably assume that the coefficient of friction between the balls and the table could be .15

If the cue ball is to be placed 1 meters from the leading billiard ball as shown below.
[ATTACH=CONFIG]60[/ATTACH]

We can than calculate the velocity the cue ball will have the moment before it contacts the set of billiard balls using common Kinematics equations.

[ATTACH=CONFIG]58[/ATTACH]

The Circled Value is the velocity of the cue ball just before it hits the first billiard ball, taking deceleration of friction into account. In this case, the Cue Ball has an instantaneous velocity of 6.005 m/s which we can safely round to 6 m/s. Therefore, because p=mv (where p is rho/momentum), the cue ball strikes the others with .96 N*s.

Therefore, based on our laws of conservation of momentum, we can determine that (since our billiard balls are all perfectly and symmetrically arranged and touching) that the momentum from the cue ball is transfered to the corner balls completely. The fact that our billiard balls are all in contact is important, because any distance between them would be closed by the impulse from the cue ball and a loss of energy (momentum as well) would be lost.

[ATTACH=CONFIG]59[/ATTACH]

In the above snapshot, we can see that the momentum of the cue ball just before impact is equal to half of the momentum given to the corner balls. Realistically, the corner balls would receive momentum roughly equivalent to M/2 because for each billiard ball that receives the momentum of the cue ball (imagine the total energy passing through each ball along the outer edges) some of that ball's momentum is transfered to the two balls in front of it, but not equivalently. Another graphic can explain this phenomena.

In the graphic, the ROYGBIV scale denotes--roughly--the vector magnitude, with Red being the greatest. Notice that the black circle indicates a close-up vector addition analysis that betrays how initially, a billiard ball may look as though it doesn't have a trajectory that lines up with the pocket, but that a normal force does indeed cause the ball to be propelled towards the corner pocket (but only of course if you are a billiards master and can hit the cue ball dead-on)!

Regardless, the setup of the game is such that the corner balls receive the most of the original momentum and are propelled towards the corner pockets. For this reason the corner balls are the billiard balls most commonly sunk by the break. In fact, a billiards player would be foolish not to take advantage of this setup on his break, physics says so

Back to math. The law of conservation of momentum (Mi=Mf) dictates that the momentum of the cue ball must equal the sum of all resulting momentum. Remember, in reality there are other momentum for each ball, but the majority of momentum goes to the corner billiard balls.

Mi=Mf => mvi=(mv)+(mv) => (mvi)=2mv => (mvi)/2m=vi/2=v

Therefore, if you apply a reasonable 20N force to a regulation 160 gram cue ball and you are GOD when it comes to aiming your cue ball for the break, you can expect each corner ball to shoot off with approximate velocity 6/2= 3m/s toward the corner pocket. :einstein)
http://www.brimbankweekly.com.au/news/national/national/general/student-helps-solve-cosmic-mystery/2176857.aspx?storypage=2a
http://news.yahoo.com/s/afp/20110527/sc_afp/australiaastrophysicsscience

This audacious undergrad made a major discovery while on break! Just goes to show the success teams of scientists can have with a fresh perspective.

For a background of the "Missing Matter" Problem, try wikipedia: http://en.wikipedia.org/wiki/Dark_matter#Observational_evidence
Superconductivity was first discovered by Dutchman and physicist Heike Kamerlingh Onnes, when Liquid Mercury was cooled to just 4.2 Kelvins!! (Using some very
expensive Liquid Helium) While measuring the resistance of the substance, Onnes found that at this specific temperature, the resistivity of the substance quite literally dropped down to nothing. Zero Ohms.

But whats the significance?

Firstly, Onnes had discovered a material that would produce no heat when an electrical current flowed through it, which has huge technical implications.

It is being discussed, for instance, whether superconductors can be used to levitate trains (the Japanese are researching a system called MagLev) or transmit power more effectively. Lesser known applications include more effective Magnetic Resonance Imaging (MRI's), more detailed SQUIDS (magnetic field sensors with a variety of applications, namely detecting brain activity), or even to shrink computers down by using smaller wires!

What's more, a fascinating phenomenon coined the Meissner Effect goes into action whenever a magnet approaches the superconductor.

[ATTACH=CONFIG]127[/ATTACH]The superconductor literally "mirrors" the approaching magnet. For example, if a north pole approaches the material, an identical north pole will be created in the superconductor, allowing the magnet to levitate at a careful height.

A more detailed description of this effect derives from essential Electromagnetic concepts, namely the popular Lenz's Law.

In a conductor, free moving electrons are always present. When a changing electric field is introduced to a conductor, these electrons seek to flow such that they perfectly cancel any changing field strengths. Unfortunately for the electrons, a great deal of resistance is present in most conductors, which prevents the flow of the electrons from canceling the change in magnetic flux. Thus, we become familiarized with a Lenz's law that provides usually only minimal resistance to flux change.

Now the crazy physics begins. In a superconductor, a substance that has negligible resistance, these electrons are able to flow in such a manner that the changing magnetic field is completely canceled! Result: Floating magnets. Whats more, is that the magnetic field doesn't need to be changing for the Meissner effect to go into action! For this reason, the Meissner effect is different than normal diamagnetism (a term that refers to conductors that follow Lenz's Law).

[ATTACH=CONFIG]126[/ATTACH]
Holy Floating Magnets, Batman! This is an example of a sample cooled with liquid nitrogen, with a cubical magnet suspended above the superconductive material. You may have noticed the thin layer of mist above the conductor; this mist is actually condensed oxygen! This oxygen jumps up to the magnet when it gets too close and quickly evaporates. This is because oxygen becomes liquid at warmer temperatures than liquid nitrogen, and also because oxygen is naturally "paramagnetic" meaning its molecules are attracted to magnetic fields a just a little bit more powerfully than other elements.

Superconductors, however, have a long way to go before they become reasonable. Numerous limitations exist. The hottest a superconductor has ever been is 138 Kelvin. The greatest challenge scientists face is getting the near perfect conditions of the laboratory into a household setting. But the future is coming! Its coming fast.
The following is a piece of an episode of MacGyver, complete with a FizziksGuy voiceover explaining a fascinating effect of physical stress of ferro materials, called the "Inverse Magnetostrictive Effect" or "Villari Effect." Although understanding this process requires very abstract thought, I highly recommend it for those of you planning to pursue E + M further into the future. It is a fascinating subject!

Its important to understand that the process you saw MacGyver use does not necessarily form magnets for all conveniently placed metal rods. MacGyver must have found himself a nearly pure rod of Iron; it is important to also understand that Iron has some RIDICULOUS reactions to magnetic fields and has very particular properties.
What this means is that banging metal on your driveway does not a magnet make. In fact, Nickel's tendency to magnetize significantly decreases under physical stress! Isn't that Iron-ic? What this means is that the actual atomic structures of individual metals determine their reaction to stress (that one goes out to all you chemistry dudes). In all my digging, it seems that Magnetostrictive material science is becoming outdated, but I gained some very valuable insight into how my Piezo Electric Violin Pickup works, the processes are not so different.

On a side note, the JWST has finally moved into Phase C (Final Design and Fabrication) and although NASA has begun hammering out strict budget rearrangements, the JWST remains on schedule!
There seems to be some problem with a certain user's blog posts and being able to view them via aplusphysics so here is a direct link to DannyBoy132's first Blog!

http://www.aplusphysics.com/forums/blog.php?16-Santa-Claus-is-REAL!!!

It's really good stuff.
NASA is currently developing a telescope to further probe the final frontier, and this new telescope, called the Webb telescope (after NASA's second administrator James Webb) or JWST, is being launched in many ways to replace the Hubble. It is designed to capture and analyze infrared light and has a primary mirror at least two and a half times larger than the original Hubble, and it is hoped that the Webb will be able to see deep into dust clouds and observe the formation of stars, planets and relay pictures of some of the universes' earliest stars. The possibilities presented are enormous, and unfortunately, the costs have been too. Regardless, Webb is scheduled to be launched sometime in 2014 and promises to be Hubble's finest successor to date. On the telescope's website are some nifty graphic tools that help contrast the Hubble and the Webb.

http://www.jwst.nasa.gov/comparison.html

The telescope will be orbiting one of only five "Lagrange" points, nearby our planet, which effectively allow 3 masses (the sun, the earth and the Webb are the gravitational forces in question) to orbit each other while staying in the same places, relative to each other. The advantages this gives the telescope are many, including more efficient communication.

On top of it all, the Webb looks just like a Star Destroyer. How cool is that?

The Webb is still in testing phase, and much of it has yet to be built, such as the large lower structure, which serves to shield the apparatus from eventually harmful rays from the sun. Because the JWST's mirrors are made of beryllium--which serves its purpose beautifully in the low, low temperatures of space--this "heat shield" is needed. To give you an idea of the massive efforts being poured into this project, a huge cryogenic test chamber (a container as cold as space) was created just to test the effectiveness of the mirror, and outfitted with giant magnets that exactly and constantly counteract gravity.

No doubt, the Webb will make a splash when it is fully functional, so stay tuned!
After doing very well on the multiple choice portion of the physics exam, I walked into the Part II questions a lot less prepared than I thought I would be. What was encouraging, though, was that even with these difficult free responses (difficult for me, personally) I feel that I could answer all of those problems perfectly if they appeared on the AP exam. Although I forgot much of what I would have needed to know on the part II (the problems were familiar but I couldn't quite get them), I'm feeling very confident that if I do what I can, I can get at least a four on the AP C exam
Just about halfway down the page that moe.ron shared on his blog is a cartoon that got me thinking. If a person had a stick one light year long (or more), and this person pushed the stick, would the kinetic energy reach the end of the stick faster than light if photons were released at the exact same moment? I'm thinking that the kinetic energy in the push would be just another energy wave moving through the particles of the stick, so I believe that the light would reach the end of the stick first, even if it would be years later.

Of course I'm hoping that someone else has a thought about the matter.

[ATTACH=CONFIG]80[/ATTACH]
I've been having serious difficulty completing all sorts of physics problems lately, and I felt that maybe I wasn't understanding the basic principles of SHM and gravitational forces etc. So naturally I turned to good 'ol Walter. But I found that instead of listening to his lectures, I was often just waiting to watch him draw a dotted line on the blackboard. So I had to re-watch a number of lectures and I was wasting a bit of time. So I turned to the other great lecture-er who some of you may not be aware of "Richard Feynman." His lectures on our current material are a bit harder to find hosted anywhere for free, so I currently own a set of Feynman lectures on CD. Its been a tremendous help to me, and although it was a bit expensive I think everyone ought to know about Feynman.

P.S. Does anyone know how many blog-posts we should have up by this time? I know I'm behind at least one.
Haven't you ever wondered why when a dog drinks water from a low bowl, its much messier than when a cat drinks from that same bowl?

Of course you haven't. But you're wondering now! So here's the physics explanation and a few accompanying videos.

The Answer: There's really not too much difference. Both the cat and the dog utilize the principal of water/liquid displacement in order to get the water to their mouths. The displaced water is then trapped in the "backwards spoon" that both animals create with their tongues. The difference between sloppy dog and cleaner cat is that the cat aims straight down (perpendicular) and uses less force to displace less water per drink while the dog uses more force to drink more water in less time. The dog also angles its head when drinking, and some water spills from the "backward spoon" as a result of earth's gravitational field imparting a force on the system. The most important difference is the force the dog uses to displace the water. The kinetic energy of the dog's tongue creates a wave in the water that sloshes all the way to the edge of a small bowl. When the crest of the wave reaches the bowl's edge: wet floor. The cat? There's just not enough force in the cat's drinking to create a wave to crest over the lip of the bowl. Remember, water molecules tend to hold their overall shape, so if at all possible, the water will fight to stay in the bowl.

I wondered if a cat the size of a greyhound would be just as sloppy as any dog, so I looked up the following video.

As you can see, this cat too drinks very neatly. But again, its simply because the cat uses less force to displace water with its tongue. Is drinking style an evolutionary trait? who knows, I'm just a physics student.
This may be the simplest device ever created with the weirdest laws of kinematics surrounding it.
What is it? Well, its a funny looking loop that flies up to 655 feet. This thing has broken world records. Thats over 6 football fields by the way. But what are the laws of physics surrounding this thing??

http://www.x-zylo.com/index.php?option=com_content&view=section&layout=blog&id=5&Itemid=38

I wish I had definitive answers. Just be observing the way that it flies, I can see that it moves like a frisbee that is thrown forward, and since a frisbee operates by creating a low pressure zone on top of itself so that it gets lift, I can only assume that this toy is magically creating a low pressure zone in front of itself…any input on this topic would really help me get a weight off my shoulders. This means you physics C!
Pre-Disclaimer: Please do not watch the attached video if you can't stand to watch blood being drawn. But by all means if you can stomach it, take this disclaimer as encouragement to continue reading.

Don't hold your breath on this one. It's very literally a video of someone giving himself a papercut in slow motion.

so how does the paper "molecular knife" muster the force to cut the skin? Like the video mentioned, it has to do with pressure exerted. Its a principle of physics that pressure is the force per unit of area that is acting perpendicular to the surface in question. We know that even though skin is weak, its difficult to apply force with your hand such that your skin breaks under the pressure. So, the incredibly small surface area of sideways paper being applied perpendicular to the skin is enough to "part the molecular sea."

Post-Disclaimer: In no way does this blog endorse self-mutilation of any kind. even if it does make you feel like micro-physics molecular moses.
These past few days of physics have been some of the most interesting of my fledgling career. Between greek letters that make my math look difficult and a crash course in Integrals, things are looking collegiate. Of course, its also been some of the most challenging physics I have done. What really excites me about the class recently is that rote memorization alone won't give me the ability to solve rotational problems. Finding a good substitute for dm often takes a certain kind of thinking that really makes me feel as if I'm cut out for the field. Personally, I feel that I'm really doing physics problems now.

On another note, I figured I'd share a certain youtube video featuring a tiny experiment in superconductivity.

This video (and concept) is one of my favorite concepts in physics. The video also serves as a great way to illustrate the abstract concept of Magnetism and Magnetic Fields. You can see as the student moves the upper magnet about the lower one, the magnet slants to the side. This is because a magnetic field has a real and physical shape, and exerts a force according to that shape. When the student coated both magnets in liquid nitrogen, he change the shape of the field. The result is that the upper magnet rests on the field at an angle, because the field is at an angle. Its something you don't always think about.

For those of you who are critical of my interest in superconductivity, check this link out. Or just read it because you like to read about advances in physics.
http://www.sciencedaily.com/releases/2006/03/060307084618.htm