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Physics the Google Way

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Physics the Google Way Physics the Google Way David W. Ward, Massachusetts Institute of Technology, Cambridge, MA “Never memorize something that you can look up.”—Albert Einstein of the page next to the calculator icon, followed Are we smarter now than Socrates was in his by web page results for the Google query. The time? Society as a whole certainly enjoys a results relevant to this article will always be higher degree of education, but humans as a those at the top of the page adjacent to the species probably don’t get intrinsically smarter calculator icon; only these can be used in with time. Our knowledge base, however, equations. Google has most of the fundamental constants built in, many of which are listed in continues to grow at an unprecedented rate, so 2 how then do we keep up? The printing press was table 1. one of the earliest technological advances that To illustrate the use of the constants in an expanded our memory and made possible our equation, consider the fine structure constant, in present intellectual capacity. We are now faced which the fundamental constants of quantum with a new technological advance of the same mechanics, electricity and magnetism, and magnitude—the internet—but how do we use it geometry are contained. We will actually google effectively? A new tool is available on Google one over the fine structure constant, as this has a (http://www.google.com) that allows a user not well know simple value. Google “(4 * pi * only to numerically evaluate equations, but to electric constant * hbar * c) / automatically perform unit analysis and (elementary charge^2) =” to find that conversion as well, with most of the it is equal to “137.035984”. We could have fundamental physical constants built in. just googled “1 / fine-structure constant” to find the same answer. Note, we were able to confirm that our calculation not The Fundamental Constants only matches the acceptable numerical value of the fine structure constant, but is unitless as well. To get a feel for how the Google calculator works, you can start by googling1 “2+2=”.You Unit Conversions can click on “More about calculator,” The previous example illustrates the utility of located directly below the result, to learn the the Google calculator in unit checking, a task basics of Google equation formatting and there which otherwise is only adequately described by you will find a link to more complete the word tedium. Although SI units have solid instructions on how to format equations for footing as a scientific standard, it is sometimes Google, e.g. “x^n” means raise x to the nth useful to employ others, or variants of SI units. power, “sqrt(x)” means take the square root This is not only because many classic texts and of x, etc. Return to the search bar and google some individual fields in physics employ units “G”, as illustrated in figure 1. Google returns other than SI, but mainly because these are not “gravitational constant = necessarily the units in which we understand the world. In the United States, a comfortable room 6.67300 × 10-11 m3 kg-1 s-2”at the top as our weight there would be “2,797.844 pounds force.” Try it for Mars or any other planet in the solar system by using “mass of planet name” and “radius of planet name” in Newton’s law of gravity. Einstein’s Car Let’s suppose you built a crazy car that converted mass into energy directly. So you put in a pound of matter, perhaps old cereal boxes, and the engine of this car converts it directly into Fig. 1. Type equations directly into the energy through Einstein’s famous energy/matter search bar, and if applicable, Google relation3, E=mc2—maybe we have to put in an outputs the result adjacent to a calculator equal dose of anti-matter to get 100% icon. Click on “More about calculator” to conversion, but we’ll assume that somehow it learn Google formatting of equations. does. Let’s suppose that it is capable of converting one pound per year under constant is one that is cooled to around 70 degrees operation. How many horsepower does this Fahrenheit, not 21.1 degrees Celsius or 294.3 engine have? Google “convert 1 pound* Kelvin. c^2 / year to horsepower” and it returns “1,732,400.85 horsepower.” It Illustrative Examples makes a Ferrari look like a go-cart. To further illustrate the advanced features of Internal Temperature of the Sun the Google calculator, we will consider several Inside the sun is a fusion engine creating heat example calculations, exploiting the Google and pressure that push everything outward from features to tailor the form of the answer we the center, but there is also gravity pulling obtain. everything in towards the center. Since the sun does not appear to be expanding or compressing, How much do I weigh on the moon?—the sun? the pressure from the heat engine at the center Space travel is fun, and though the internet must be equal to the gravitational pressure. If we won’t allow us to do it from the comfort of our assume that the sun is composed entirely of homes, we can get a sense of what it would be hydrogen, i.e. protons, and that the hydrogen like to visit another planet, without the harmful atoms behave like an ideal gas within the side effects of toxic atmospheres and unbearable volume of the sun, then the temperature due to temperatures, see figure 2. Since our weight, not this internal pressure is given by the familiar our mass, is just the gravitational attraction we ideal gas law, PV=nKT, where P is the internal experience to the local gravity, we can use pressure, V is the volume of the sun, n is the Newton’s law of gravity to determine what we number of hydrogen atoms (protons) that make would weigh on other planets. If on earth our up the sun, K is Boltzmann’s constant relating weight was 100 pounds of force, which is the heat energy to temperature, and T is the number our bathroom scale indicates, then our temperature of the sun, which is the quantity we mass would be 100 pounds. If we took our scale seek. The pressure from the sun’s gravity is just to the moon then to find out what the scale the force of the sun’s gravity on itself divided by would read there, google “convert (G*mass the surface area of the sun. Plugging all of this of the moon*100 pounds/(radius into the ideal gas law and solving for T, we can of the moon)^2) to pounds force” google the resulting equation to find our to find the answer “16.5912317 pounds estimate of the Sun’s temperature at its center: force.” Replace the moon with the sun “(G * proton mass * mass of the to find that we would need to take a better scale sun) / (Boltzmann constant * radius of the sun) = long Name Shorthand 23,118,268.8 Kelvin, or ~2.3x107 K.” atomic mass units amu or u Compared to the accepted value of 1.5x107 K, Astronomical Unit au this is not a bad estimate considering the Avogadro’s number N_A approximations used. By the way, how did I Bolzmann constant k know to use the Boltzmann rather the Rydberg electric constant, permittivity of free epsilon_0 constant in this problem? I originally used the space Rydberg constant, but got an answer in electron mass m_e electron volt eV Kelvins/mol, while I expected an answer in elementary charge Kelvins. Faraday constant fine-structure constant Electrostatic Versus Gravitational Force gravitational constant G Physics as we know it was born with Sir Isaac magnetic constant, permeability of mu_0 Newton’s Mathematical Principles of Natural free space 4 Philosophy or simply the Principia in 1687. magnetic flux quantum The seminal equation from this work is the law mass of the moon m_moon of gravitational attraction, which contains the mass of the sun m_sun gravitational constant, G. To illustrate the use of mass of [planet name] m_mercury,… the gravitational law, google “(G*mass of molar gas constant R the earth*mass of the sun/(1 Planck’s constant h and hbar astronomical unit)^2)” to find that proton mass m_p the force binding the earth to the sun is radius of the moon r_moon radius of the sun r_sun “3.54296305 × 1022 Newtons.” Using 2 radius of [planet name] r_mercury,… the equation for centripetal acceleration, a=v /r, Rydberg constant the earth’s rotational speed can be determined. speed of light c To do so google “sqrt(G*mass of the speed of sound (note: in air at sea sun/(1 astronomical unit))” to learn level) that the earth is hurling through space at the rate Stefan Boltzmann constant “29,785.5982 m/s.” One hundred years after the publication of the Principia, Charles Augustin Coulomb published, Table 1. Guide to physical constants in his second memoir on electricity and available on Google calculator. Entries magnetism, the law that bares his name; are sometimes case sensitive. Coulomb’s law is analogous to Newton’s law of gravitation, with the masses replaced by charge, Had we simply asked for the electrical force and the gravitational constant replaced by the between them instead of the ratio we would find -08 Coulomb constant which is now known to be that the force is equal to “1.85205315×10 1/4πε , where ε is the permittivity of free space, pounds force,” using the Bohr radius as 0 0 5 or electric constant.
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