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aweld98

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  1. aweld98
    Since I am a ballet dancer, it would be fair to mention one of the most impressive ballet moves performed: the grand jete. For non-dancers, this move can be described as a "split like jump"; the dancer takes off by extending one leg into the air and taking off into a projectile type motion.  In the best case scenario, the ballerina hits a perfect split at the peak of her parabolic path, creating a split second mesmerizing image for the audience to enjoy.  In order to complete this leap, several physics ideas must be thought of and considered carefully. First off would be the gathering of energy. It is impossible, no matter how strong your legs are or how much experience you have, to perform a grand jete from a static position.  A dancer usually performs a series of quick moving steps across the floor in order to gain the momentum and more importantly, kinetic energy. Hence, when the dancer extends his or her leg at an angle to the horizontal stage (creating projectile motion) this gathered kinetic energy is transferred into potential energy, allowing the dancer to follow a parabolic path.  What allows the dancer to hit a peak of their motion in a split and to appear almost frozen in mid air would be the lack of gravitational acceleration downward. For a split second, at the top of the dancer's path, their upward vertical acceleration has been reduced to zero and they are yet to experience a gravitational force downward.  Finally, it is important to note the purpose of inertia and center of mass during the execution of this step. When taking off for the grand jete, a dancer must work to keep their torso (primary center of mass) moving in the direction of their anticipated projectile; in other words, the dancer must anticipate the jump. If not, their inertia will resist this upward change in motion, which will limit the success of the grand jete. Crazy that so much physics goes into this ballet step. 
  2. aweld98

    Pointe Shoe Physics

    By aweld98,

    When I was a little girl learning to dance, I dreamed of the day that I would put on a pair of pointe shoes and twirl like Clara from Tchaikovsky's "The Nutcracker".  Little did I know that pointe shoes make dancing about a million times more difficult and more painful.  Besides the basic discomfort that a ballerina experiences when squeezing her foot into an unconventionally shaped and small shoe, there are also a great amount of physics that go with explaining why pointe shoes are not the dreamy things that they appear to be.  For starters, the pain is unbearable, and the reason why has to do with the combination of surface area and gravity.  When a person walks normally, they are displacing the force of their body (their mass multiplied times their acceleration), over their two feet.  When you think about, that is actually a relatively small surface to hold up a human's weight, but because human feet grow with weight as children mature into adults, holding up one's weight on two feet is not a burden; rather, it is quite natural.  When a ballerina first begins to dance, she learns to "twirl" and pirouette on "demi-pointe," or quite simply, on the ball of her foot.  Doing so divides the surface area for weight distribution in half, which makes it more difficult to oppose the force of gravity that may pull her off balance.  After years of strength build up, dancing on demi pointe becomes almost as natural as walking because the ballerina has gained the strength to hold up her same weight over a smaller surface area.  However, when a ballerina puts on her pointe shoes, she nearly quarters the surface area which she had to work with when she danced on demi pointe.  In pointe shoes, all of the ballerina's weight is centered on a surface area that is about one by two inches.  Even if the dancer's weight has not changed, because the surface area is reduced, the force of her weight is all on her toes, which in real life would have very little experience in holding up the weight of a human.  This strong force often times does work (W=Fd)  on the dancer's toes; gravity pushes the toes further down into the pointe shoe, and the friction between the shoes and toes does work on the toes as well, causing them to burn and bleed.  Also, because pointe shoes lower surface area, the ballerina must adjust her center of mass to be over her her toe so she does not fall, when naturally the center of mass of a human is more so centered over the middle of the foot.  Crazy to think that so much physics goes into just putting on and standing in a pointe shoe, let alone dancing in one, but for all little ballerinas, they dream of that moment.
     
  3. aweld98

    Fouette Turns

    By aweld98,

    I used to be a ballet dancer, and I remember that one of the hardest skills to learn and master was the fouette turn.  This move requires the ballerina to extend her leg out and then bring it quickly in, all while completing a turn (see diagram below for clarity).  These turns can go on forever, and the secret behind their infinite completion is all based in the idea of conservation of angular momentum.  Angular momentum is equal to the moment of inertia (I) multiplied by omega (w).  Moment of inertia is determined by the integral  of the radius squared multiplied by dm; because the mass of the dancer is unchanging during the turn sequence, the only factor that will influence her moment of inertia is her radius.  So, when the dancer begins her turn sequence, she has her leg extended out in front of her, causing the radius of her body to be larger and therefore her moment of Inertia to increase; consequently, at this point in the turn, her angular velocity is rather low.  However, when she whips her leg in, her radius decreases, causing her moment of Inertia to decrease proportionally.  Because of the law of conservation of angular momentum, the angular momentum at the start of the turn must equal the angular momentum when the dancer whips her leg in.  Because angular momentum = Iw, a decrease in I will result in an increase in w and vice versa in order to fulfill the law of conservation of angular momentum.  So, when the dancer whips her leg in, causing her moment of Inertia to decrease, her angular velocity must increase in order to compensate and conserve momentum; the increased angular velocity allows the dancer to complete a revolution and extend her leg out again and so and so forth.  Hence, these turns can go on forever because angular momentum must be conserved; the only way to stop them is to provide a net torque to stop the rotation, or, more often then not, to lose your balance and fall over!

  4. aweld98

    Metronomes

    By aweld98,

    A very useful device for many instrumentalists and musicians, in particularly string players, is a metronome. A mechanical metronome is a box like object that produces a steady beat. A musician sets this beat based on the tempo marking of the piece which they are practicing, and then the beats produced by the metronome help the musician to play at a steady pace and to avoid rushing or slowing. So, how does a metronome work?  Well, from the outside, a metronome actually appears like an upside down pendulum; at the top there is a weight which is attached to the bottom of the box by a long rod. The musician can adjust the speed of the beats produced by lowering or raising this top weight.  The way the metronome works is that at the bottom of this rod (and usually hidden from view) is a weight that acts like the bottom bob of a pendulum. So, when the instrumentalist lowers or raises the upper weight, they are in essence shortening or lengthening the length of the pendulum, hence increasing or decreasing the frequency of the simple harmonic motion and the tempo of the produced beats. 
  5. aweld98

    Bumper Cars

    By aweld98,

    In the summer, one of the best things to do is to go to an amusement park.  For me, I cannot handle too many crazy, twisting roller coasters, but I love bumper cars.  And, as it turns out, bumper cars have many applications of both momentum and dynamics in the way they function and how they impact the riders.  For instance, when a bumper car and its passengers bump into another bumper car and its passengers, both cars and their passengers experience a change in direction; usually, if the car was originally traveling forwards, it ends up traveling in the backward direction after the collision.  Why?  Well, it all lies in the idea of conservation of momentum, that the momentum before equals the momentum after.  If one considers the two cars as a system, their momentum before is the sum of the mass of each car multiplied by its velocity.  This momentum is some number, and the momentum after the collision must equal this number.  So, the cars must "rebound" off of each other in the opposite direction of which they were traveling in order to fulfill the law of conservation of momentum.  But one must also consider the passengers who are driving the cars.  One of the funnest parts about the bumper cars is the kind of jolt the passengers feel when they crash into another car.  So, why do riders feel like they are going to head bang the steering wheel?  The answer is inertia.  Inertia is the idea that objects resist a change in motion.  So, when the collision between the bumper cars causes a change in direction of the bumper cars (conservation of momentum), the riders launch forward because that is the direction in which they were traveling.  Because humans have significant mass and therefore inertia (mass is directly proportional to inertia), the bodies resist the change in motion of the bumper car by continuing in the direction they were originally traveling in.  Luckily, a seat belt or lap bar stops riders from flying out of the car, and the bumper car madness continues.
  6. aweld98

    Tubing

    By aweld98,

    The start of November and its corresponding cold weather is making me miss summer more and more!  One of my all time favorite summer activities is tubing because it is so fun and thrilling.  Tubing has applications of both tangential  velocity as well as centripetal velocity and acceleration.  For example, when the boat makes a turn, causing the riders to go outside the wake of the boat, the tube and its riders are subject to a centripetal force caused by the tension in the rope.  Why?  Well, at the moment of the turn, the boat becomes like the center of a circle, with the radius being the length of the rope attached to the tube and the edge of the circle being the tube and its passengers.  This idea becomes more clear when riders are slingshot from the wake of the boat, because then they are actually experiencing centripetal movement and force; this part of the ride is also the most thrilling.  When the riders are experiencing this centripetal movement, they are traveling at a velocity that is tangential to the radius of the circle, which would be, in this case, the rope attached to the tube and the boat.  If a rider is unfortunate enough to fall off while they are experiencing centripetal motion, they will not fall off in the direction of the circle; rather, they will fall off in the direction which is perpendicular to the circle, because that is the direction in which their tangential velocity vector points.  The tube also as this tangential velocity, but the centripetal force caused by the tension of the rope keeps the tube traveling in the path of the circle.  Who knew there were so many physics applications in this fun summer activity!
  7. aweld98

    Johnny English Pendulum

    By aweld98,

    Like I said in my last blog post, I love spy movies, and I think I am starting to love them more and more because of all the physics applications in them.  While Bond movies are awesome, I would say my all time favorite film would be Johnny English starring Rowan Atkinson, most known for his role of playing Mr. Bean.  In the film, Atkinson plays a mock agent, and pretty much no one takes him seriously or believes that he can be successful at anything.  However, after several mess ups, Johnny manages to save the day by preventing the villain, Pascal, from being crowned the new King of England.  The way he accomplishes this task is rather unorthodox, and it applies the physics concepts of a pendulum.  As the Bishop of Canterbury is about to place the crown on Pascal's crown at the alter of Westminster Abbey, English, who is in the balcony, grabs hold of a free cable, and in an almost "Tarzan-like" manner, swings from the balcony and grabs the crown.  While his foil of the coronation is successful, English then has a slight problem: he cannot get off of the swinging rope.  See, when he swung, English did not understand the principle of conservation of energy as well as air resistance.  For starters, he reaches for a pole on the opposite side of the swing that is above where he swung from; by conservation of energy, he would not have enough energy to get to a height higher than where he started from because that would require more energy to be converted into potential.  As a result, English misses the grab and is hopelessly swinging back and forth.  Then, thanks to air resistance, the distance of the swings becomes shorter, and he is forced to come face to face with Pascal, who by that point has a gun aimed at him.  But, in English's clumsy fashion, he survives and saves the day!
  8. aweld98

    Tennis and Rain

    By aweld98,

    This past week, my tennis team had its final matches before sectionals begin tomorrow.  However, due to heavy rainfall, several of our matches were either rescheduled or postponed.  Naturally, I thought that there had to be some physics dealing with the impact of rain on the total force of friction when one plays on a court.  Turns out that a liquid substance like water decreases the coefficient of friction of the surface it is on (in this case the tennis courts).  Because tennis requires a lot of quick stopping and changing of direction, friction is essential for both speed and for staying on one's feet.  A decrease in the coefficient of friction would mean that it would take longer to stop and turn than it would on a dry court.  Not only that, but a decrease in friction makes stopping, in general, more difficult, which could prove dangerous for players on the court.  So, our postponed matches were not in vain; our coaches were trying to protect us from friction, or rather, the lack thereof!
  9. aweld98

    First Physics Blog

    By aweld98,

    This is my first blog for AP Physics C, which I will hopefully update weekly throughout the upcoming school year.  Some of my activities outside of school include playing tennis, practicing the violin, and participating in the theater program at school.  When I am not participating in any of these activities, I am listening to music or hanging out with friends.  I have one younger sister who is now a freshman in high school, and she's pretty cool.  I am taking AP-C Physics because I was successful in and really enjoyed Physics B with Mr. Powlin last year.  That class was the first science where I really applied math to solve actual problems and began to understand certain mysteries and concepts that govern everyday life, which I found really fascinating.  I hope that AP-C Physics can help me expand on what I learned last year and prepare me for the rigor I should expect in college.  I definitely want to pursue a career in the science and/or math field, so I hope this class can give me insight to what I might study and experience in the future.  I am excited to take this course because I want to be challenged along with my friends; on that same token, I am a bit scared about what is to come in AP-C Physics, but I am sure that, no matter what, it will be a very rewarding year in this course.
  10. aweld98

    Crime Shows

    By aweld98,

    I have a bit of lagging start on my blog posts for this quarter, but here's to hoping that I can get back on track and start blogging weekly.  One of my favorite types of TV shows to watch are cop and crime shows because I love their mystery and thrill.  Recently, I was watching an episode of Castle when one of the main detectives was shot by a suspect.  For a solid two minutes, I thought that one my favorite character had died because he just lay their, completely still.  In the end, it turned out that he was okay because he had been wearing his bullet vest.  So, why did the bullet knock the wind out of him?  Well, it is all an application of Newton's forces and momentum.  When the bullet was fired at the detective, the extremely strong and friction high material, be it metal or Kevlar, slowed the bullet down and stopped it from penetrating the detective's skin (F=ma).  However, because the detective was wearing the vest that absorbed the bullet, and because momentum is always conserved, the shot caused the detective to move with a certain velocity in the same vector direction that the bullet had originally traveled in.  This velocity knocked the detective off on his balance, causing him to fall to the ground and get knocked out.  So, the detective was not knocked out from the bullet, but rather from the transfer of the bullet's momentum, making him a lucky man to be alive and me a happy viewer knowing that I can watch him on future episodes.
  11. aweld98
    I spent this summer internship working in a remote sensing lab.  My job was to analyze Landsat satellite imagery in order to analyze the impact of wildfire on vegetation growth in Akagera National Park in Rwanda.  I was able to do this analysis because of the data provided by the satellite.  Satellite orbits are possible because of the strong gravitational field of the Earth and the relative masses of the satellite and the Earth.  For example, for the Landsat 8 imagery that I analyzed, the force of gravity felt by both the satellite and the Earth was equal to G(mass of the earth)(mass of Landsat 8)/(radius of Landsat's orbit)^2.  Thanks to Newton's third law, both the Earth and the satellite felt this same force due to the other's existence.  However, the mass of the Earth is exponentially greater than that of the satellite, so the satellite orbits in the Earth instead of the Earth orbiting the satellite.  This orbit takes the form of centripetal motion, where the centripetal force is equal to the force of gravity which is equal to (mass of Landsat)(velocity)^2/(radius of orbit).  This centripetal motion keeps the satellite constantly changing direction and therefore constantly accelerating.  Thanks to gravity and the laws of motion, scientists can view the Earth from above, and I was able to complete my research this summer!
  12. aweld98

    Trampolines

    By aweld98,

    As a kid, I was always at my neighbor's house because they always had the newest and coolest trampoline.  Turns out that this cool contraption requires many physics concepts in order to work. The energies required for a spring are kinetic energy, gravitational potential energy, and spring potential energy.  When you bend your knees in order to take your first jump, you are using your gravitational force downward in order to compress the spring in the trampoline (work from your knees is transferred into spring potential energy). Then the spring releases, and the potential energy transfers into work done on your body, hence shooting you up into the air!
  13. aweld98

    Swinging on Swings

    By aweld98,

    One of my favorite activities as a young kid was to play on the playground; I loved the monkey bars and slides, but one of my all time favorite thing to do would be to swing on a swing.  Swings give the sensation of flying, which is probably why I loved them so much.  Ironically, the way a swing works happens to revolve a lot around the conservation of energy.  Think about it: In order to start swinging, someone has to either give the swing a push, or the swinger must kick themselves off of the ground.  As one swings back and forth, they must continue to pump their legs because otherwise they will lose the battle to air resistance and slowly but surely come to an eventual stop.  As one swings and gains elevation, all of the energy from the leg pumping becomes potential energy, which varies directly with the height of the swing from the ground.  For a split second, when all of the kinetic energy is converted into potential and the swing is at its peak, the swing stops (as a kid and admittedly now, that is my favorite part).  Then, as the swing accelerates towards the ground, the potential energy becomes kinetic, resulting in maximum speed at the bottom of swinging motion.  In fact, a swing is very much like a pendulum in terms of how energy works to keep the participant swinging and how energy is transferred and conserved.
  14. aweld98

    Calculus Pup

    By aweld98,

    I just returned from a calc group session at school with my friends and our calculus teacher.  My friend, in an attempt to make Taylor Polynomials and series less of a burden, brought along her little dog.  Ironically, as I was sitting there, the pup inspired what I am afraid will be my final blog post of my AP Physics C year.  Well, my friend had gotten up from her seat, and the dog, which was tied by a leash to the chair, wanted a change of scenery.  As a result, she attempted to jump onto the very chair which she was tied onto.  However, as soon as her paws came in contact with the chair, she skid across the surface of the chair and nearly fell off the opposite side.  So, what did the little doggy fail to consider in her take off towards the chair?  Well, there are a few factors.  First off, when the dog took off from her hind legs, she made an angle with the floor; she had both horizontal and vertical components to her velocity.  As a result, when she hit the peak of her trajectory path, hence landing on the chair, her vertical velocity was zero, but her body continued to move in the horizontal direction due to the horizontal component of her velocity.  In addition, because the surface of the chair is slicker than most surfaces, resulting in a lower coefficient of friction, there was little frictional net force present in order to decelerate her horizontal velocity.  Ideally, in order to prevent any skidding, the dog would simply have jumped completely vertical and landed on the chair, hence having zero horizontal velocity (this application is not ideal, however, because it would involve the dog jumping through the solid seat of the chair, which is impossible and would hurt, to say the least).  However, a large angle with the horizontal would increase the sine component of her velocity and minimize her horizontal velocity, and therefore skidding.
  15. aweld98

    Snow, Ice, and Car Turns

    By aweld98,

    In a previous blog post I wrote about how the lower coefficient of friction due to ice causes a decrease in rotational motion and an increase in skidding when someone is driving.  I want to extend on that topic only because a few weeks ago, when the snow was really bad, I first hand experienced the horror of making a turn without a strong centripetal force present.  It was rather snowy and icy, and my friend was driving.  However, as they went to make the turn, they turned too sharply, and we skid all over the road.  Luckily, we gained control of the car and neither of us were injured; either way, it was a terrifying experience.  Why did we skid?  Well, part of it does have to do with the reduced coefficient of friction in ice because, in a turn, friction acts as the centripetal force that keeps the object moving in a circle.  However, another notable point would be the width of the radius of the turn.  When my friend went to make the turn, they cut the corner kind of tightly, resulting in a much tighter centripetal radius.  Because centripetal force is equal to mv^2/r, a decrease in the length of the radius means that the centripetal force to keep an object moving in that circular direction must increase.  Coupled with the reduced force of friction caused by the slippery ice, it is no wonder that the car strayed from the circular path which it was taken around the bend!
  16. aweld98

    Static Shock

    By aweld98,

    Yesterday, as I climbed into bed, bundled up in blankets and a heavy sweatshirt, I reached across by bed to grab a final blanket.  All of the sudden, out of the darkness I saw a spark, which was followed by a stinging feeling in my finger.  Had I not learned about electrostatics, I probably would have screamed and thought that there was something wrong with me or that the house was on fire.  However, physics helped me to understand that I was not dying and that what had happened was simply an attempt of two objects to reach electrostatic equilibrium.  As I was bundling up, I was unknowingly rubbing my heavy sweater against my blankets; as a result, electrons were transferred from that blanket onto the sweater (and therefore me), causing me to become a charged object.  When I reach for another object, in this case the other blanket, which was uncharged, some of the electrons on me "jumped" onto the blanket in order to reach equilibrium.  This transfer of electrons was both seen in the milisecond spark and felt through the hand that I had used to grab the blanket.
  17. aweld98
    Unless you are living under a rock, you would know that March Madness and the beloved basketball season are officially coming to a close.  As sad as this end may be for some die hard basketball fans, it should be noted that the sport of basketball (like most other things in our world) is possible only due to the presence of physics.  While there are many possible applications of physics, from the friction between the shoes of the players and the court, to the tension (or lack thereof) in the strings of the basketball hoop, I would like to draw attention to the most important part of the game: shooting a hoop.  When a basketball player takes a shot, they are in essence sending the basketball into a path that is very similar to that of a projectile.  However, the basketball player must take into account their distance from the hoop and the height of the hoop when taking their shot.  As a result, some shots seem to go higher (due to a larger angle of projection), while other shots seem to be more horizontal in nature due to a smaller angle of projection.  Why?  Well, when the angle of projection is increased, the y-component of the ball's velocity increases due to the sinecomponent of the angle, so the ball goes faster and further in the y-direction.  The opposite is true for smaller angles of projection.
  18. aweld98
    This past Saturday before I got sick, I helped a fellow Physics C student plant a community garden for a service project.  While I was laying down rows of tulip bulbs and fertilizer, I got to thinking about plants and how important gravity is to their growth.  The roots of plants grow down into the soil in the direction of the gravitational field; plants need soil for nutrients and water, which are key elements for their survival.  Without gravity, roots wouldn't have a direction to grow in, nor would they have a force keeping them rooted in the ground.  As a result, we would have floated plants that would have no way of acquiring nutrients from the ground, and they would therefore have no way to survive.  We all know that without plants there would be no humans, so we sure are lucky to have gravity keeping our plants rooted and healthy.
  19. aweld98
    For winter break, I traveled with my friend to southern Florida in order to escape the chilling winds and snow.  Yesterday, as we returned from our sunny break and descended into our final destination, I applied physics in a kind of unique way.  As the plane got closer and closer to the ground, the turbulence became increasingly worse (the pilot had warned us that this was expected due to strong winds).  As the descend continued and the bumpiness of the ride worsened, I heard a little boy in front of me grow more and more uneasy and scared.  At one point, he asked his dad "What if we just drop out of the sky?".  I thought about it, and I realized that the boy had no need to worry of the plane simply falling out of the sky.  Why?  Well, if you simplify it, a plane descending is simply an application of kinematics and projectile motion.  Even if the pilot were to completely cut the engines, the plane would still continue to go at the same horizontal speed because there is no acceleration in that plane (granted, as I did mention, there was some wind, which could cause a resisting drag force, but the wind did not have nearly enough force to decelerate the plane's velocity to a magnitude of zero instantaneously).  Even if the plane were to go into freefall, it would continue to travel in the forward motion, but the acceleration due to gravity would increase, hence the planes downward displacement would be increasing faster in comparison to its displacement in the y direction.  Even so, given the conditions, the little passenger in front of me had no need to worry; we were not going to simply fall out of the sky, and we safely landed on the runaway.
  20. aweld98

    Plant Growth in Space

    By aweld98,

    In my last blog I wrote about how essential gravity is to plants growth on Earth, so I decided to find out how plants can grow in space where the force of gravity is significantly smaller and/or non existent.  Turns out that plants can and have been grown on the International Space Station.  How?  Well, plants have an inner ability to orient their growth away from their seeds; it is almost like they know that they need to grow away from the seeds in order to access water and nutrients for survival.  Also, because the Space Station orbits the Earth, plants were able to grow correctly due to the pull of gravity on the station.  Even though the force of gravity on the plants is fractionally smaller on the ISS than it is on Earth, the plants wer orbiting close enough to the earth that they could still obtain an instinct on how to grow based on their relatively close proximity to Earth's gravitational pull.  Finally, while gravity serves as a guide for where plants should grow to on Earth, in space, moisture and nutrients replace gravity as this guide; so, plants grow towards the moisture and nutrients in space just like they would grow towards gravity on Earth.  While growth in space is certainly not perfect, it is most certainly possible, due to the plants' previous abilities and adaptations.
  21. aweld98

    Dangerous Driving

    By aweld98,

    After much anticipation and a not very white Christmas, it is finally snowing outside.  Well, it is more like a blizzard, but either way I am stoked because if actually feels like winter.  Anyways, this morning I had rehearsal for the school show and was eager to jump in the car and drive to school; my parents, however,  were not as keen on my operating the car on this cold and snowy day.  Don't get me wrong, I am not a bad driver, but the weather conditions, especially the ice, made my parents reluctant on allowing me to brave the storm alone.  After some persuasion, I was handed the keys to the car and was on my way.  However, on the ride to school, I started to think about the physics behind why driving in the winter is so dangerous.  Here's what I came up with.  Despite the obvious concerns, such as limited visibility, a primary concern of drivers (and of mine while en route to school this morning) is the danger of sliding or skidding of the road.  Why is it that the number of skidding cars increases exponentially during the winter season?  It all has to do with the difference in the coefficient of friction of ice.  The wheel of a car will spin thanks to the torque and work done by the car's engine.  However, the reason that the car moves is because the friction of the road acts in the opposite direction of the wheels motion, hence opposing sliding and allowing the car wheels to turn and the car wheel to rotate.  However, when the road is covered with ice ( which has a significantly lower coefficient of friction),  sometimes the force of friction is not great enough.  The lack of a strong frictional force will cause the wheel and therefore the car to slide.  Hence, driving in the winter does have its hazards!  

  22. aweld98

    Mozart No. 5

    By aweld98,

    Yesterday at my violin lesson, my violin teacher spent the entire hour working with me on cleaning up my sound quality (I am playing a Mozart Concerto, so the sound has to be crisp and clean).  The main thing my teacher suggested in order to get rid of the crunchy and unclear sound I was producing was to apply a greater force to the bow.  After only a few tries, my sound became significantly clearer.  I figured there had to be some physics behind why a larger force resulted in a clearer tone.  Us violinists put rosin, a white colored powder, on our bows in order to increase the friction and therefore the force between the bow and the strings (friction, of course, exists already between the bow and the violin when there is no rosin, but rosin increases the friction, which stops the bow from sliding and consequently, the violinist from losing control.  If there were no friction between the bow and the strings, then the strings would not vibrate and there would be no music created.  The violinist then applies a  force (depending on the direction in which they are bowing), so that they can overcome the force of friction and get the bow to move with a certain velocity (work = change in kinetic energy application).  Music is created because the friction between the bow and the string causes the bow to "catch" the string; in other words, the bow grips the string, then releases it, then grips it then releases, etc.  This motion occurs over and over as the bow moves up and down, resulting in oscillations of the string which translate into sound.  If a violinist does not apply enough force, then they cannot overcome the static friction between the bow and the string.  So, the string does not vibrate; the scratchy sound is produced from the lack of vibration and from the work which the smaller force is doing on the string (conservation of energy application). By applying a larger force, the violinist fully overcomes the static friction, which allows the bow to catch the string and then for the string to release and to continue this oscillation, which results in a much purer and enjoyable sound.
  23. aweld98

    Sledding

    By aweld98,

    I will have to apologize in advance, but the snow outside has me really excited, so the next few blog posts may very well be about winter physics.  One thing that I am very excited to do now that it is officially winter, is sledding/tubing.  As I am not a very good skier or snow boarder, I opt for the easier version; sitting and allowing gravity to do the rest.  All of these downhill, winter activities, however, are possible thanks to conservation of energy and friction.  Conservation of energy is necessary in order to attain speed as one goes down the hill.  To start, when one is at the top of the hill, all energy is in the form of potential energy (U=mgh).  However, as one goes down the hill, the height from the bottom decreases, so the potential energy decreases.  As a result, the kinetic energy (K=.5mv^2) increases in order to compensate for the decrease in potential energy (conservation fo energy).  Another factor that seems important in these activities is friction.  The coefficient of friction for ice and snow is lower than that of say grass, and it makes sense.  You can't go skiing or sledding down the side of a grassy mountain because the force of the friction up the hill caused by the grass is greater than the force of the skier or sledder (mgsintheta).  So, it is necessary to have a material (ice or snow) that has a lower coefficient of friction in order to get going down the hill.  I can't wait to get out on the slopes and let friction and energy do their jobs!
  24. aweld98

    Bridges and Mutes

    By aweld98,

    At first glance, this blog post may appear to be about the physics behind a large civil structure on which vehicles and human beings move across.  However, that is not the case.  This post is about the importance and purpose of a bridge in the structure and function of a violin, as well as the impact a mute has on a violin's performance.  On the violin, the bridge is a wooden structure perpendicular to the rest of the violin; it sits atop the wooden face of the violin, and the four strings lie across the top of it.  The purpose of the bridge is to transmit the vibration of the four strings into sound.  Let me explain.  The various strings on a violin (and any stringed instrument for that matter) vibrate, hence creating sound waves, when some type of work is done to them (in the case of the violin, the most common way to get this vibration is to pluck the string or play it by applying pressure with a bow).  However, these vibrations do not directly translate into beautiful music.  So, the bridge serves to transmit vibrations to the structural part of the violin, which gives the vibrations more space to vibrate on and throughout; instead of vibrating a thin string, the vibrations ring throughout the entire structure, causing an increase in volume and projection of music.  Another component worth mentioning would be the impact of a mute on the bridge and this transmittance of vibrations and sound.  A mute is placed directly on the bridge whenever a musician wishes to dampen their sound.  How does it work?  Well, the mute reduces the vibration that occurs on the bridge during the transfer of sound from the strings to the wooden structure of the violin.  As a result, the amount of vibrations transferred to the main structure are significantly reduced, resulting in a less vibrations throughout the entire instrument and a noticeably softer sound.
  25. aweld98
    My last blog post was about the impact of rain on the coefficient of friction on a tennis court, and Mr. Baker commented about how different it is to play on clay tennis courts; I totally agree!  I rarely play on clay courts, but when I do, it is not at all an enjoyable experience because the ball does not seem to travel as fast.  I decided to find out why.  Turns out that clay courts have a higher coefficient of friction than the grass at Wimbledon or other regulation courts.  Turns out that the clay surface decreases the balls momentum, (p=mv), causing shots that would be quick to be more dull.  The reason the momentum decreases is because lose clay clamps around the ball, causing an increase to the already higher force of friction.  Because of the conservation of momentum, even the slightest increase to the tennis balls mass (tiny bits of clay) will cause a decrease in the ball's velocity after it hits the ground.  This decrease in velocity gives the opponent more time to strike the ball, hence decreasing the effect of a hard, well angled shot. I guess it wasn't just my imagination that points seemed duller and shots didn't seem as hard to hit on clay courts; clay courts really do impact the shots and the time opponents have to hit returns!

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