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.