A Year of Physics

Wow! I believe that this is our last physics blog. Well, its been an interesting year and I have definitely learned a lot. For my last physics blog, I feel that it is fitting to return to my first post, where I told my impressions of the first four weeks of class. At that point I felt as though physics was a tightrope that I was struggling to balance on. This feeling lasted through the year, as physics is a fun, yet dificult subject.

In this blog, I am going to talk about something similar to a tight rope, a see-saw. When I was little an in Georgia I used to play on a big wooden sea-saw all the time. A see-saw is a great example of torque. Torque is measured by force times the cross product of the lever arm. This can be useful in figuring out where to sit on a see-saw to make it balanced with people of different weights. The lever arm of a see-saw is measured from the fulcrum where the weight of just the board can be balanced. In other words, if there are two people of the same weight they would need to sit the same distance from the fulcrum, but on opposite sides. If one person weighs twice the other, the lighter person needs to sit twice as far from the fulcrum as the other.

Hard work...or is it?

Last weekend was the OBDA Select Stage Band concert in Seto Hall. I played the Bari Sax in this band and as usual got tired while caring my saxophone all around campus, band room to Seto Hall and back. My saxophone in its case is pretty heavy, but sadly, as I have learned from physics I do not do any work while I carry it, no matter how heavy it is, how long I carry it, or how tired I get.

Work is force x distance but since when I carry my saxophone I am applying force in an upward direction while I am walking forward, the force and distance vectors are perpendicular and so no work is being done.

I do however do a small amount of work while moving my saxophone and interestingly enough, the more times I stop and rest, the more work I do. Why? Because when I pick-up my saxophone I am in fact doing work, even though I am not while walking. When I lift my saxophone I am applying an upward force of the mass times the acceleration of my saxophone, and because it is also moving a distance in the same direction (upwards) work is being done as calculated by equation Work=force times displacement.

Also, when I am standing still with my saxophone it has potential energy of mass times g times the height at which I am holding the case.

(Sorry I do not have my actual saxophone to take a picture of, but this painting gives the general idea)

Boats and Buoyancy

This week as I was reviewing for Physics Quizzes I realized that I didn't remember much about buoyancy, so I've decided to use this topic for this week's blog. This is a picture of a boat sailing in Pearl Harbor. This boat is obviously floating, which, in other words, means that the buoyant force pushing up on it from the water is equal to the weight of the water that the boat displaces. Buoyant force can be calculated by calculating the weight of the displaced water by using the density formula (density of water is 1000 Kg/s and the volume is the volume of the boat beneath the water) and then multiplying this mass by 9.8 m/s^2 (gravity).

To calculate what percent of the boat is underwater using the fact that the weight of the displaced water and the buoyant force are equal. Density times volume can be substituted for the mass and then a ration between volume and density can be found, telling what percent of the boat is underwater.

Stage Band Fair Performance

This Friday at the Iolani Fair the stage bands performed in the entertainment tent. Typically, during concerts, each or every other saxophone, one trombone, one trumpet, and the singer get microphones so they can be balanced by the sound crew and be heard while they solo. Microphones use the properties of diodes to amplify sound as it runs from the instrument to the microphone, and eventually to the speaker.

A microphone and speaker system consists of a transistor which has an n-zone filled with "holes" and a p-zone filled with electrons. These two areas are connected with an n-channel that allows electrons to flow and a current to flow. In a transistor that is attached to a microphone, when there is no sound, such as when a singer is quiet, there is no potential difference running through the transistor and a depletion zone is created where electrons cannot flow. On the other hand, if a loud sound is played, the potential difference causes electrons to flow readily through the n-channel and a large current is produced, thus causing an amplified sound to be produced at the speaker.

Rainbow Projector

This rainbow projector that I used to watch when I was younger uses properties of reflection to create a rainbow that spans across a bedroom wall. The projector emits a rainbow of light from the top. This light is shone upon a convex mirror which enlarges the image (in this case projection) and also creates an arc shaped image. Convex mirrors magnify images and are often used for store security as they allow a person to see a wider range of objects as they gather light from an angle larger than concave or planer mirrors.

The rainbow image that is produced by this device is projected because the light source is placed slightly behind the mirror so that the angle of incidence is great. The angle of incidence equals the angle of refraction so the image is projected out of the device and onto a wall. The arc-shape of the rainbow is created because the mirror is convex so the different light rays intersect with the mirror at slightly different angles causing them to be reflected in the shape of both the mirror and a traditional rainbow.

Winter Ball Snow Globe

In this cool snow-globe we got at Winter-Ball, you can see a great example of refraction. In the picture you see the picture, or object, and the picture "magnified" through the globe, or the image. This refraction occurs similarly to how the object refracted in our Cheese-box experiment. The picture refracts because the index of refraction of water is greater than the index of refraction of air, about 1.33 to 1. Using Snell's Law we can determine the angle of refraction of the object. Snell's Law is n2sin(theta)=n2sin(theta) where the first theta is the angle of incidence of the light hitting the object. Because the snow-globe is round the light refracts only once and because the picture in the snow-globe takes up most of the globe, it each point on the picture refracts equally and the picture appears to be magnified.

Also, if you turn the snow-globe there is a point where you can no longer see the image. This is where total internal refraction occurs. Total internal refraction occurs at a critical angle as found by the equation Sinc=n2/n1, so in this case it is about 49 degrees from the center of the picture.

Glasses, more than meets the eye

As many of you know, I wear glasses because I am nearsighted, meaning I cannot easily see objects that are far away. In order to correct this, I wear glasses that help to bring faraway images to a focus at the retina in the back of my eye, so my brain can receive and interpret them with maximum clarity. Because I am nearsighted, I see images at twenty feet that other people can see at say fifty or sixty feet (I'm not quite sure what my prescription is) away. When images enter my eye they are created at some distance in front of my retina whereas images in the eyes of farsighted people are focused behind the retina. In order to move the focus of images in my eye backward, I need to wear diverging lenses that cause incoming light rays to intersect at a point farther from the source as they diverge (get farther apart by refraction) while coming through the lens, thus they do not meet until they reach a father back location. On the other hand, if I were farsighted, I would have to wear converging lenses that cause rays to intersect closer after leaving the lens as they in a way push the rays of light closer as they are refracted at a smaller angle as they go through the lens.

Transformer

There are many transformers in my neighborhood as I suspect is the same in any neighborhood. Without these transformers our homes would not get the power that they need and nothing electrical would work. The need for transformers is due to the fact that power comes from the plant through electrical lines at very high voltages, into the tens of thousands! Most household appliances, however, operate on only a few hundred volts. So, there needs to be a way to reduce the power from its high voltage to a more usable voltage. This is where a transformer helps. Inside a transformer there are many coils, but lets just focus on two for the general concept. The two coils are separated by an iron core and as the full high voltage from the plant comes into the first coil a magnetic field is generated through the iron to the second coil and an emf is induced. This in turn creates a current in the second coil and this passes through a resistor and the emf becomes what is necessary for the resistor. The number of coils in the first and second coils also varies. The equation V1/V2=N1/N2 shows this as V is the emf and N is the number of loops, showing that the emf decreases proportionally to the number of loops on each side of the transformer.

Hand-Cranked Radio

Yesterday during the tsunami warning my parents found our hand-cranked radio that could run without electricity or batteries. But what really makes this radio run? Physics, of course! Recently we have been studying electromagnetism and so now I can explain how something can have power with no power source. Inside this radio (I'm assuming) there is a coil of wire attached to the radio. This wire will act as a generator and the person turning the crank will supply the necessary energy. As the mechanism is cranked energy is supplied and the small wire moves in a magnetic field. Because this wire moves in a magnetic field an emf is induced and thus a current is created. Since power equals current times voltage, the radio has power and can turn on. The power can be stronger due to more loops in the wire, turning the crank faster (greater angular velocity), a greater area within the wire, and more time. Conservation of energy applies here but some energy is lost to heat.

Flashlight Circuit

A flashlight is a good example of a simple

circuit. Inside this flashlight there are two batteries

connected in series along with a light builb and

metal connecting all of the components. The

flashlight's on-off switch completes the circuit when

it is switched on by moving a piece of metal into

place, thus completing the metal circuit relaying the

battery potential difference to the light bulb.

The amount of current running through the circuit

is found with the equation V=IR where V is the

voltage of the battery and R is the resistance across

the light bulb. Because the batteries are connected

in series the power or P=IV of the light bulb is greater than it would be with just one battery. In

order for the light bulb to stay lit, the circuit must remain completed by the on switch so that the

current is able to flow and complete the circuit.

Also, the Potential difference or voltage across the battery must be countered by the resistance in

the lightbulb so the voltage in the wire as it returns to the battery is 0V.

The Oven and Stove Top

Today as my mom and I were baking cookies to eat during the Super Bowl, I realized that our oven is a great representation of Physics concepts. A convection oven heats and cooks by convection which is heating through a fluid medium by movement of fluid. In an oven the heat that comes off of the coils rises and the surrounding heat sinks. This motion repeats and eventually cooks whatever is in the oven.

Also, the top of the oven shows the concepts of resistance and power. The coils that you place pans and pots on while cooking heat up due to electric current. The power that goes into the stove is equal to the current times the voltage. The coils then heat up due to this power. The heat that eventually comes off of the coils to heat up the food is equal to the current squared times the resistance of the coils. As the coils heat up, the resistance increases as shown in the equation P=I^2R. This heat is transfered to the food by conduction and as a side effect of the increase in temperature of the coils the resistance increases.

Electrical Wires

Electrical wires are an everyday thing, but after studying electrostatics, I am now able to better explain how they work. These are some of the wires that power my TV, DVD player, etc. Obviously, in order to power electrical devises, a charge must be carried to them. To do this, a conductor such as the copper in an electrical cord, is needed to allow the charge to flow from the outlet to the TV. The cords must be capable of handling enough current to power the TV without shorting the circuit, as happens with an overload of current.

As a little kid, whenever I unplugged something, I was always told to pull the cord out of the socket by pulling on the plastic part. This was because the plastic covering on the electrical cord "insulates" the cord and stops the charge from flowing from the copper to my hand or any other substance, and keeps people safe from electric shock.

If you have ever seen an electric shock, lightning, or some kind of electric spark, it can also be explained with electrostatics. The visible transfer of charge results in the "spark" or lightning that we see in such energy transfers. Such visible transfers are simply made by an extreme change in the electric potential of a system where a large number of charged particles are transferred to an area with less charged particles such as the ground, a lightning rod, the air, and even a person's hand. I have had many personal experiences with lightning and it is amazing to think that the enormous lightning bolt that flashes through the sky is really made up of a lot of, singularly invisible, charges.

Staticky Hair

Many times, especially during the winter, you will find your hair standing on end due to "static electricity". Even though we usually associate this phenomenon with rubbing a balloon on your head to create static, I have found that this also occurs on airplanes or while wearing a winter hat. Often when moving after leaning back on an airplane headrest or taking off a winter hat, my hair will stick to the previously mentioned surface. This is due to the opposite charges of my hair and the object. When two objects are rubbed together, they can become charged as electrons move from one object to the other. In the situation with hair, electrons probably move out of the chair or hat, making it positively charged with excess protons, and into my hair giving it an excess of electrons and making it negatively charged. Since the two objects are then oppositely charged, they attract, sticking together as I try to pull them apart. Throughout this process, charged is conserved as electrons are transferred between objects and not lost.

FRC Robotics Prototypes

Yesterday we spent six hours at robotics working on prototypes for our new robot. I spent my time on the kicker team working to build a kicker where we could vary the force and therefore the distance that it kicked a soccer ball. We managed to kick 34 feet! This involved a lot of physics, so much so that we had to borrow a force sensor from Doc. (Thanks Doc!) Our robot kicker is a "foot" attached to a "leg" with holes in it with rubber tubing strung through it. When we tighten the rubber tubes and then pull the foot back, the potential energy in the foot is great, so that when we released the foot it sprung forward and kicked the ball. After we got this prototype working, our coach asked us to find out how much force we needed to apply for each distance the ball was kicked (for later programming use I believe). So we borrowed a force sensor and attached it to the tubing. We had already figured out that the more strands of tube we used, the more force, and therefore the further the ball traveled. This means that force and displacement are directly related, therefore the spring constant equation applied (Force = K x displacement). So with the force sensor attached, our kicker team kicked the ball using the four different amounts of tubing, measured the distance the ball traveled and the force of the tube, then collected the data for the spring constant.

We also discovered that the robot kicks with projectile motion, and we kicked the ball over a 18(ish) inch obstacle that was 25 feet away. If we say that the ball went about 1.5 meters in the air after each kick then we can use kinematics (deltaY=Vvi T+.5Ay T^2) to find that it takes .55 seconds to reach the ground 34 feet (10.36 meters)away. Therefore we can use (X=ViT) to find that the initial velocity of the ball is 18.8 meters/seconds.

The Refrigerator

Surprisingly, a refrigerator can be considered a heat engine. This statement almost sounds like a paradox, but no, a fridge is actually a heat engine that does negative work. A heat engine is a system where heat is transferred into a "tank" where the pressure caused an increase in volume which pushes a piston up, causing it do work (force times displacement). in conventional heat engines such as those in cars, the system does positive work as more heat enters the system as leaves (work =Qin- Qout). In a refrigerator negative work is done as more heat flows out than in causing the piston to move in a direction that opposes the force (Qin-Qout=negative). Work is also equal to Q-deltaU so if Qnet is negative Work is negative, the system cools, and a refrigerator is formed. I think it is pretty cool that a heat engine and refrigerator work the same way, just opposite. A car engine and refrigerator both do work but one is positive and the other is negative.

Hot, Flat, and Crowded

The novel Hot, Flat, and Crowded by Thomas Friedman is a very intriguing and thought provoking book that I thoroughly enjoyed reading. This book is an “eye-opener” as it tells how if we, in this generation, do not do anything to care for the environment and make the planet more green, the earth will be near unlivable due to population growth and temperature increase by as early as 2050, well within our lifetime.

This novel is fascinating as it tells about the nature of people and why we need to change in order to help the planet. Friedman explains that people are only interested in what will easily make them money or in what will directly affect them in the near future. However, in order to save the planet for future generations, people now have to make sacrifices. I completely agree with this analysis and think that the government and governments around the world, especially in fast growing countries like China, need to impose laws with environmental standards such as gas and coal taxes, as this book suggests.

I believe that this book makes many good points about the United States and I agree that we need to set an example for the world by “going green”. I concur that if we do this by reducing our reliance on oil, we will not only increase our efficiency and ingenuity, but will also become a more independent nation.

I enjoyed Friedman’s view of the future with the “Smart Black Box”, and I think that if everyone in the world cooperates we can achieve a similar situation in a matter of years. I agree with his proposition that this would require the education of people in many countries on the ways of energy efficiency, which would not only increase the standard of living around the world, but would help to improve environmental conditions by raising awareness. I think that these ideas are essential to the world and implementing them is going to be the only way of protecting the earth for years to come.

I believe that this book truly represents the world today as well as what we should strive for it to be in the future. This book has a very important message and should be read by everyone.