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Today we're going to talk about the world's biggest cheetah (and for once I'm not talking about Brady). As we all know, cheetahs are the fastest land mammal and can reach speeds of up to 110 km/hr (that's 30.56 m/s for you physics purists out there) and are the only member of the genus Acinonyx. But what you probably don't know is how a cheetah is able to run so fast and change direction quickly enough to catch its prey. The secret lies in the cheetah's tail. If you watch a video of a cheetah running (instead of doing your webassign) you can see that when the cheetah changes direction, it flicks its tail like a rudder to steer itself. Like a car, if a cheetah were to attempt a tight turn at a high speed, it would tip over. This is due to the rotational inertia of the cheetah/car and the torque provided to accelerate it. The flicking of the tail provides a reactive torque that counteracts the tipping motion and helps the cheetah stay upright. In fact, the cheetah's tail is so effective that engineers in South Africa have developed a car that is able to turn sharply at high speeds with the help of a tail like structure in the rear. This design could help emergency vehicles move much faster ad potentially save lives.

One of the practice AP questions in this unit's packet gave me a little trouble when it asked what the force of gravity would be at the center of a planet. Mathematically, it would make sense that gravity is strongest at the center of the planet because gravitational force is inversely proportional to the square of the distance between the centers of mass of the two objects. But if gravity is a product of mass, then once the object reaches the center, it would be equally pulled in all directions by the two halves of the planet. Would this mean that one would be weightless at the center of the Earth? According to something called the Shell Theorem, no gravitational force is exerted on an object inside a symmetrical spherical shell regardless of the size of the shell or the objects location within it. If this is true, then that would allow a person to scoop out a large perfectly spherical section in the center of the earth and enjoy weightlessness. Of course the pressure at the center of the Earth would likely crush such a structure, but if a material that could withstand such heat and pressure could be synthesized, then one could theoretically float around deep beneath the surface. Of course any of this is incredibly impractical, but it does give scientific credence to the Dwayne "The Rock" Johnson movie, Journey to the Center of the Earth (not that such a masterpiece needed it).

The other day I was walking a dog when I saw a rather strange sight. Two men were sitting in a driveway in a beat-up old pickup waiting to turn onto the main road. On the back of this pickup truck was a massive pile of furniture. I quickly counted an armoire, four chairs, a table, and a dresser all balances precariously on top of each other. While a normal human being would have secured this unstable load in one way or another, these two men decided to take a laissez faire approach. They left the back of the pickup truck open and used a total of zero straps to fasten the pile. they were relying entirely on the static friction between the bed of the truck and the legs of the furniture. Unfortunately, as they peeles away, it became clear that they had never had the benefit of hearing Bill Nye say that "inertia is a property of matter." Perhaps the furniture wanted to stay at its old home, or perhaps it merely adhered to the laws of the physical universe, but it fell off the truck. It didn't even get out of the driveway. From what I could see, most of the furniture was still salvageable (save a missing leg or two from some of the chairs), but the lesson to be learned here is that you should have at least a basic understanding of physical properties if you want to be a mover in such a highly competitive field.

An aspect of drag force I had not considered before was momentum. When an object runs into air molecules, momentum is conserved. This would imply that resisting force is caused by the bombardment of the object by air molecules. Since momentum is directly proportional to velocity, it would stand to reason that drag force is also proportional to velocity. Additionally, it makes sense that by changing the momentum of the air molecules, a force is exerted. This force acts to slow the object down (or keep it aloft in the case of an airplane). Of course, air resistance is much more complicated than that and must look at infinitely more factors, but the idea of air resistance as conservation of momentum was interesting

Does this really have to do with physics? Trick question: everything has to do with physics. #betterthanearthscience

Sometimes I work as a part-time gardener to make enough money to support my lavish lifestyle. The other day I was attempting to break off a dead branch that was an eyesore and also conveniently placed at a height where a passerby might bump his or her noggin on it and sue for millions. So I needed to take it down. At first I tried breaking it with sheer force. Despite my manliness and ripped biceps, I could not seem to break the sturdy limb. The branch would bend but it would not break, as I was not applying enough torque. So naturally I busted out my physics reference table to see what equations might be of help. Of course then I realized that torque would be helpful in this situation. As Mr. Tytler once told me, if you build a long enough lever, you can take the lug bolt off a tire with your little finger. So I gathered a shovel and some duct tape and made the branch almost twice as long. This time when I applied a downward force, the branch snapped and made a loud noise that scared many squirrels. Torque is directly proportional to length, so by making exerting the same force from farther away, I was able to break the branch. The important thing is that I got paid and was able to go spend lavishly that weekend.

How can you be sure that your friends were not being sponsored by either company and that you were not a victim of a vicious guerrilla marketing campaign?

As you know, space is a vacuum. This means there is no friction. Using this reasoning I ridiculed the characters of the low-budget 1970s Star Wars knock-off Battlestar Galactica when they claimed they could only turn off the engines to their spaceship and drift for a small amount of time. Couldn't they just accelerate to a fast speed, turn off their engines, and just coast to their destination. After all, there is no friction to slow them down. This would greatly expand their range and cut down on fuel costs. Unfortunately, it turns out I may have been wrong. Space is not as empty as we have been led to believe. In fact, there are many things in space such as hydrogen gas and space dust. These should have an extremely low drag coefficient and provide negligible friction. However, the drag equation shows that drag force is proportional to velocity, so if the ship were going at a very high speed (as intergalactic spacecraft must), it would undoubtedly encounter some friction. This explains why a ship cannot just coast indefinitely and why the actors on the television show were right and I was wrong.

In the strange discipline that is quantum physics there are many facets that are equal parts fascinating and confusing. One of these is Max Tegmark's thought experiment known as quantum suicide. In his thought experiment (which could only occur in his mind, as there is no way to test this theory in the real world), a man sits in a room with a gun. The trigger is linked to monitor the spin of a quantum particle. When the man pulls the trigger and the particle is detected to be spinning clockwise, the gun will go off and kill him. If the particle is spinning the other way, the gun will not fire and he will live. So what happens when he pulls the trigger? The gun clicks and he lives. What happens if he pulls the trigger again? He still lives. This process will continue in perpetuity, thus making the man immortal. In reality, the man is both alive and dead at the same time. This is because every time the man pulls the trigger, the universe splits in two. In one universe the man dies and in one he is still alive. The man is not aware of this split, so he does not know he is both dead and alive. This theory is known as the Many-Worlds Theory. This theory postulates that with every decision made the universe splits into two alternate realities. This allows the man to exist in a state of quantum immortality, as he is unaware that his counterparts in the parallel universes have died. This theory has gained more traction in recent years and holds very serious implications. For example, there could exist a parallel universe where the Nazis were victorious in World War II, or a universe in which I actually get my calculus homework done. The implications for both science-fiction nerds and scientists are quite far-reaching, but nature of quantum particles and their mechanics are still murky. This field has made great strides in recent years, but there is still so much that is unknown, which makes it difficult to say anything definitively. However, the Many-Worlds Theory and Tegmark's quantum suicide experiment are interesting things to think about.

While I was throwing bricks at the neighbor's cat the other day, a strange thought occurred to me: why is it that a rubber ball will bounce when it hits the ground bu these bricks do not. To answer that question I turned to my trusty frenemy physics. The reason a rubber ball bounces is because it is made out of an elastic material. This means that, like an elastic band, it can be bent and stretched but still return to its normal shape. When a ball hits the ground (or the neighbor's cat), the surface exerts a force on the ball that deforms it. The kinetic energy of the ball is transformed into elastic energy that is stored in the ball as it is deformed (this process occurs faster than the human eye can perceive). Like a spring, the ball must return to equilibrium, so the elastic energy is converted back into kinetic that translates into upward motion. Of course some energy is lost to air resistance, heat, and sound. Bricks do not have this elastic principle, and if too great a force is exerted on them, the brick will shatter. Their propensity to bounce back to you is why elastic objects are a much better choice for pelting that nefarious cat.

One of the greatest myths in popular culture is that if one were to go into outer space without a spacesuit then their blood would boil and they would explode. Neither of these things are true. While the lack of pressure would lower the boiling point of your blood and cause your bodily fluids to expand, the only ill effects would be very painful swelling. The stretchiness of your skin would prevent you from exploding (I wonder what the spring constant of human skin is). Rather than instantly exploding, you would drift about in immense pain for about 15 seconds or so until your body uses up its oxygen supply and you pass out. You could try to call for help in that small time window, but as we know space is a vacuum where there are no air molecules to vibrate and create sound waves, so no one can hear you scream. So while you won't explode from being hurled out of an airlock, it probably isn't something you want to be doing in your spare time.

One of mankind's greatest inventions is the automatic door. The idea that one once had to actually push or pull open the door to a department store now seems barbaric. But how do these marvels of modern engineering work? How does the omnipotent sliding door know that we, the humble customers, are there and require entrance to the establishment. Most automatic doors operate using a motion sensor. Motion sensors work by sending out microwaves and detecting motion using the same principle that astronomers use to determine if a galaxy is moving toward us or away from us. When door sends out microwaves, objects reflect them back to the sensor. Objects that are static send back the same wavelength as the original signal, but moving objects (like a person or stray cat) alter the wavelength through the Doppler effect. When the reflected microwaves are of a different wavelength, the door knows to open and let the customer in. This is a cool application of the Doppler effect and something to think about next time you go to Wegmans to return some stale chips.

While perusing the internet in order to further delay my impending calculus homework, I came across this picture. While I did not Google "studly old man in pool with head and forearm detached from body," I found it anyway. While the average medieval peasant might think this image the work of black magic or Photoshop, I as a student of physics recognized it as merely a demonstration of the wave properties of light. The reason his head and forearm are not attached to the rest of his body is because the light reflected off it is refracted by the water an the glass wall of the pool. The water and the glass have a higher index of refraction than standard air, so when the light comes off the man's muscular body and travels from the water to the glass to the air, it is refracted at each transition by an angle theta. Because of this angle of refraction and because the human eye cannot perceive reflected or refracted light waves, it appears as though the man's body is at a different location than his head and forearm. So the man is not some sort of mutant with a head coming out of his arm. Outside of his devilishly good looks, he is just an ordinary dude, and light played a trick on us.

After recently binge watching Star Wars, Star Trek, and Battlestar Galactica as part of another attempt to put off Calc homework, I realized an error common to almost all space related moving pictures. During their frequent shots of large ships flying through space, the sound of the ships' engines can often be heard. However, because space is a vacuum, there can be no sound in space. Without air molecules to vibrate, how can the sound of the ship's engines be heard? While it does make those ubiquitous shots less boring, it is an oversight on the account of George Lucas and all the other film makers who tried to piggy-back off of his success.

It being near October 25th and having nothing else to do (with the obvious exception of last week's calculus homework), I found myself re-watching the Back to the Future trilogy. While the verity of the physics in these movies regarding time travel are questionable at best, I was more concerned with another facet of the film. In the second movie, there is a scene in which Marty McFly steals a hoverboard from a defenseless child in 2015 to escape Griff Tannen and his gang of futuristic toughs. McFly seems to be getting away despite having never set foot on a hoverboard in his life when all of a sudden he travels over a pond in the town square and the hoverboard ceases to go forward. One of Griff's goons proceeds to explain that "hoverboards don't work on water." This left me asking why. It appears that the hoverboard can travel over land without any significant propulsion, but the instant it encounters water it stops. However, the hoverboard does not immediately sink and leave McFly underwater; instead it hovers above the water. It would seem that if hoverboards don't work over water, the first thing to stop working would be the hovering part. Finally, I realized that like their ancient counterparts, skateboards, hoverboards rely on their rider's momentum to move forward. When Marty goes out over the water, air resistance slows him down to a stop, and there is no way for him to propel himself. Assuming the hoverboard operates using superconductors and magnets like many of the prototypes in development today, this would still allow it to hover above the water but not travel forward unless hooked up to some external propulsion system. But the question still remains: when will we get the flying cars and $50 Pepsis that Hollywood promised us?

During the football unit in gym class last week, I was balling so hard that one might confuse me with a diamond when I noticed witnessed a spectacular catch. A fellow baller, let's call him Duron (as that is his name), leaped up to snag a wayward pass with one hand. Somehow he was able to bring it down with him to much admiration from his classmates. Hating to be shown up, I later attempted a similar catch, but the ball simply bounced off my hand and I was left looking like a fool. I later realized that Duron was able to make the catch by applying the concept of momentum. As we know from last year, change in momentum is equal to F∆t. When Duron went up to make the catch, he moved his arm backward with the ball, so as to allow the change in momentum to occur over a longer time, therefore decreasing the force of the ball on his hand. When I tried to make the catch, my arm was rigid and failed to move in the direction of the ball, so it exerted too great a force on my hand to be caught. If I had only applied my knowledge of physics at the time, I would have been able to show that I was the best baller on the field. Alas, it was instead proved that my constant iteration of the mantra "ball is life" was untrue in my circumstances. Therefore, I will stay in school and not pursue a career on any professional sports team.

Your perspective is truly eye-opening and insightful. You are definitely right to pursue a job right out of college so you can get that paper. Dollar dollar bills y'all. Keep up the first-rate work. I'm sure your blog will be incredibly fascinating and educational.

This is the first post on a blog. This blog is about physics. I am the author of this blog. I hope this blog will help me improve my spelling and grammar, which are terrible but do not prevent me from making fun of other people's. There is nothing remarkable about me other than the fact that I can make minute rice in 58 seconds. I am writing this blog for AP Physics C, a class which I took by accident but have grown to love. I have grown to appreciate the rigor of this class and recognize it as a college style class. While none of my professors at whatever university I attend will have the same cachet as Mr. Fullerton, I hope this class will better prepare me for the style of instruction in college. I also enjoy that there is no lab period, meaning I have an extra free period every other day during which I can do nothing and tell terrible jokes to anyone who will listen. I hope to get out of this class a better idea of what physics is all about. The introductory course I took with Mr. Powlin was excellent, but the content only scratched the surface of the deep field of physics. Hopefully, by the end of the year I will either love or hate physics enough to decide if it is worth pursuing in college. I am excited to learn many new things that will help me grow as a pretentious doofus who uses physics to prove people wrong or just make myself sound smarter than I really am. I am also excited to take a class in which the responsibility to get work done rests solely upon my shoulders. Consequently, I am anxious to take a class where the responsibility to get work done rests solely on my shoulders. Hopefully, I will be able to motivate myself with snacks. Either way, I will emerge from this class with all my limbs intact, and I will declare victory.