# jfrachioni

Members

24

1

## Blog Entries posted by jfrachioni

i don't know if its a law, but as a kid I've always been told to walk on the right side of the road. whether we have adopted this because someone decided that people should have a dedicated side of the road to walk on, or for some other social reason, im here to tell you why its a good idea from a physics standpoint. at least here in america, where the cars drive on the right side as well, physics says that people are safer when they walk on the right. it all has to do with relative velocities. when cars and people are going in the same direction, the velocity of the car relative to the person is less than the velocity of a car relative to a person when people travel in the direction opposite traffic, as when people walk on the left side. what does this mean? if a person traveling on the right is hit by a car, the relative velocity of the car is less than that of a person traveling on the left, so the acceleration of the person on the right would be greater, resulting in more injury.
i thought because i started my bloggery with a prediction and outlook of the course, that i should end it all with an analysis of the year. my thoughts on Mr. Fullerton as a teacher are that he is great at explaining things, and teaching in general. the course is very difficult, and he makes it easier to handle. i also think independent units are a good thing, and that they should be continued. as for blogs, i definitely think writing can help cement understanding of physics concepts, however my opinion is that there are less painful ways of doing so than writing blogs. although I only took half a year of calc, i found the material i learned in that half was more than enough to carry me through this course, yet a whole year would have probably provided me with an even better understanding of this material. i think there should be more projects, contests at the end of the year, and less kerbal, although the kerbal program was extremely educational and interesting, so the best thing may be a balance of the two. all in all, its over and im looking forward to college.
have you ever tried forging currency? i know i have. turns out, its not as easy as it looks. paper money has many copy-resistant properties that people can use to distinguish real from fake money. one example of this is the ink used to print a portion of the bill. this ink is special because it changes color depending on the angle it is looked at. this is achieved by infusing the ink with microscopic prisms that have sides that reflect different wavelengths of light. they also have strips of paper inside of them with ink that glows under ultraviolet light. like the highlighters i discussed in a previous post, these strips have a special chemical that turns the ultraviolet light into visible light, a trait that is very useful for detecting fake money.
have you ever wondered how your refrigerator gets things cold? i have. turns out, refrigerators use the same physics to cool things as air conditioners, dehumidifiers, and many other household devices. what happens is there is a compressor, two coils of tubing, and an aperture; all working together to make your beverages so damn frosty. if you listen to a refrigerator, what you probably hear is the compressor. the compressor uses electricity to create pressure in the external coil, letting it expel energy as heat, then the gas flows through the aperture and expands, soaking up the same amount of energy from inside the fridge as it just expelled through the external coil. this process is repeated, and the heat is effectively pumped out of the fridge. this principle can be demonstrated with a aerosol can. when you push the nozzle down for a few seconds, the can gets cool. this is because it soaks up the energy from your hand as the gas expands, much in the same way the gasses do in the fridge.
highlighters can be useful in many situations, and when you highlight something, it is pretty surprising how bright they look. the other day i was wondering this exact thought, so i decided to look it up. when you see a color, the amount of light entering your eyes is usually the same as the amount of visible light of those frequencies the color reflects at you, however, with highlighter ink, this isn't the case. when you highlight something, apparently the color you see actually creates its own light. visible light, that is. As i found, highlighter ink contains an ingredient that takes invisible light like infra-red and ultraviolet that are emitted along with visible light in most light sources and turns them into visible light, making the ink look brighter than the light that shines on it. the fact that we know how to do this is amazing to me.
I made the transition from regular to electric toothbrush a month or two ago, and aside from the noticeable improvement in my oral hygiene, I've been thinking about how the toothbrush charges. I understand the manufacturers motivation for not using exposed electrical contacts, as such a design may let water inside, however i found the alternative to be far more puzzling. when you want to charge it, conveniently, you only have to place it on the peg protruding from the base plugged into the wall. With a design including no electrical contact between base and brush, i was confused as to how energy was passed between the devices, however now i think i have an answer. what i think is that the energy in the base is sent to the brush through a magnetic field. there are two coils, one in the brush, and one in the base. when the base is energized, the magnetic field it creates envelops the brush coil, inducing a current, and charging the battery. physics is truly everywhere.
recently, ive been interested in space exploration. not so much exploring stuff, but specifically life aboard the international space station. As one can imagine, everyday tasks we think little about on earth can be pretty complicated without gravity. on earth, we dont have much expirience with surface tension because gravity tends to have far more of an affect on liquids. In space, however, the absence of gravity results in surface tension being much more noticeable, and extremely useful. because the space station is filled with equiptment that is expensive and necissary, yet vulnerable to water, the fact that water likes to stick to itself is useful because when astronauts clean, drink or in general when water is floating about, the water contains itself and doesn't go flying into the nearest piece of machinery. even with simple tasks, like eating lunch, astronauts will sometimes take advantage of water tension to keep an object in place; placing a dab of water on the bottom of a can and placing it on the table to keep it from floating off.

in the picture, you see a blob of free floating water in space, with an air bubble chilling inside, just because it can.
a few days ago, i put a plastic water bottle in the freezer, hoping that it would cool more rapidly than if i had put it in the fridge. accidentally, i ended up forgetting about it, and a few hours later when i opened the freezer, i witnessed an intriguing phenomenon. when i opened the fridge, i expected the water to be completely frozen, however to my surprise, it was still liquid. after taking the bottle out and placing it on the counter, something else completely unexpected happened; the water immediately began crystallizing. my mind was blown as i saw the wave of ice overcome that which was once liquid. in a matter of seconds, the transformation was complete. Why did this happen? through a little research, i soon found the answer. among much speculation, most sources seemed to agree that the delayed crystallization occurred because the water was too still to crystallize when its temperature dropped below freezing. apparently the crystallization process of any material needs some encouragement. what works most of the time is the ambient vibrations of the refrigerator, or other things, lightly tapping the molecules into their crystal structure. for whatever reason, those vibrations weren't enough to get my water bottle to crystallize, however what was enough was the slight tap on the counter as i removed it. the tap shook the molecules enough for a small group to fall into their crystal structure and freeze. with the presence of that small initial crystal, or what smart people like to call a seed crystal, the rest of the water molecules started falling into place around the starting point, the crystal growing to the size of the entire bottle. physics can be pretty mysterious.
there has been a large amount of misconception around this topic, a major contributor being the fact that people mix cornstarch and water and call it a non-newtonian fluid, when in fact it is only a colloid. colloids are not fluids, as they are heterogeneous, consisting of liquid and fine particle mix. they have changing viscosity because the particles cant flow away as fast as the liquid, and are bunched together as a pseudo solid. this is different from a non newtonian fluid because the fluid changes viscosity because it is in a near-crystalline state, and acts like a crystalline solid as pressure is applied. some examples of this are jolly ranchers(corn starch), some types of bullet proof glass, and shampoo
i have a problem. every time i pick up a cat to let it fall to its death, it manages to turn around mid air and land square on its feet, even when im not giving it any initial rotational speed. the law of conservation of angular momentum says that the cat can not start rotating after i have dropped it, assuming it starts with no angular momentum at all. so how they do it? turns out, they actually bend themselves into a v shape in mid air, breaking their rotational axis in two. this lets them turn their front half against their bottom half via muscles in their torso, resulting in both rotational motion along the center of mass, and along each side of the v they created with their body. this allows them to quickly spin around while still conserving their total angular momentum. when theyve turned 180 degrees, the cat simply bends out from the v shape, into what is more or less a line, in which state the cats is not turning at all, because the net angular momentum must be zero, conserved from the beginning. therefore, cats are immortal.
yesterday i opened the window in my room because it was particularly warm outside, and throughout the day as i entered and left my room, i would accidently slam my door, even though i was accelerating it to the same speed to close it as i usually do. as i got used to my now much easier to close door, i thought about possible explainations for this annoying phenomenon. i hypothesized that the culprit was my open window. i figured that when the window was closed, the shutting of my door was harder because while shutting, i was doing work not only on the door, but also on the gasses inside my room because the door acted like a plunger, increasing the volume of my room faster than air could enter and decreasing the pressure inside. with my window open, gas can come in both through the window and through the crack under the door, increasing the speed at which air could enter, therefore decreasing the difference between the rate of incoming air and the rate of increasing volume. with this difference smaller, the door does less work on the air inside because it doesnt need to decrease the pressure to close. with the window closed, i was used to giving more speed to the door to close it, but now that the window is open and less of the energy i give the door is used to change pressure, the speed i usually use is too much, and the door slams.
usually, when shot at, the average person would have neither the reaction time, nor the hair strength to deflect a bullet with a braid of his hair. the mere thought of such an impulse delivered to a bullet without crushing it or harming the hair seems to go against all physics, however for those of you who have seen the movie pootie tang, starring pootie tang, you know that pootie dont need no words, pootie dont need no music, and apparently pootie dont need no physics.