# Tag Info

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Feynman rote this in his Feynman Lectures on Physics Vol. 2, pg. 1-9.

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The concept of inertia is indeed useful in two ways. I think your notion of it as a technical promotion of the everyday word "sloth" (without the baggage given it by the Roman Catholic translation of the "deadly sin" Ἀκηδία) as extremely close to the mark. In physics the notion of "inertia" has two, very alike uses: The first is practical, through a weak ...

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This page has a helpful summary of the history--it seems he initially accepted the Aristotelian idea that objects could only continue to move if some "force" inside them was moving them (keep in mind this is before his technical definition of 'force'), and it took him a while to switch to the idea that bodies naturally tend to keep moving unless acted on by ...

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There is at least one philosopher before Plato and he is Anaximander. There are many passages in his works that relate to the concept of symmetry: The basic elements of nature (water, air, fire, earth) which the first Greek philosophers believed that constituted the universe represent in fact the primordial forces of previous thought. Their collision ...

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Apparently it's a historical quirk. Characterizing spectral lines as principle, sharp, or diffuse dates back to the 1870s with the works of George Liveing and Sir James Dewar. Living and Dewar also noted that these lines appear in series. Arno Bergmann discovered a fourth series in 1907, which he labeled as the fundamental series. If Arnold Somerfeld had ...

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To be exact Einstein made a claim that it is gravity that curves space-time. You can follow his reasoning in his "Relativity: The Special and General Theory." Einstein started off with comparing acceleration caused by gravity to acceleration in a lift (assuming it moves with accelerated motion) going up. He claimed that these two accelerations are ...

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According to the excellent and very well researched scientific biography "Subtle is the Lord" by A. Pais, as late as 1912 Einstein was still assuming a flat Euclidean space (at that point he had been working on the general theory for 5 years). Then (in 1912) Some time between August 10 and August 16, it became clear to Einstein that Riemannian geometry ...

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Opening with an aside: Interestingly, one of Feynman's students, Carver Mead, of VLSI fame, expressed similar dissatisfaction with these EM lectures and actually wrote a monograph, "Collective Electrodynamics", which attempts to reformulate the discipline using the potentials, not the fields, as the primary entities, and quantum systems (superconducting ...

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Newton very much relied on the works of his predecessors, and sometimes his contemporaries. This is what scientists do do, and should do. Newton did not "figure out" his universal law of gravitation completely on his own. He instead expanded upon the works of Galileo, Kepler, Halley, Huygens, Hooke, and others. There are issues with regard to priority for ...

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Although the story of the apple is most likely made up, Newton did try to find a connection between the motion of falling objects, the Moon, and the planets. He started with the acceleration of an object moving at constant speed $v$ in a circle. Within a small time interval $\Delta t$ the object sweeps out an angle $\Delta \theta$. The change in direction of ...

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Well, there are 4 parts to the right-hand side; let's look at each in turn. The first $M$ is the mass of the gravitating body. You would expect that the force it exerts should be larger if it has a larger mass. Moreover, it's not unreasonable to think the force should be directly proportional to this mass: twice as much mass should grab things with twice as ...

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When did they know that light and other electromagnetic wave doesn't need a medium? Physicists had an inkling early in the 20th century with the development of Planck's law in 1900, Einstein's development of special relativity in 1905, and Einstein's explanation of the photoelectric effect, also in 1905. This strongly suggested that electromagnetism was ...

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The Michelson-Morley experiment was the first good evidence they had that there is no luminiferous aether, and was conducted in 1887. (Michelson had an experiment in 1881 trying to do the same, but it was flawed)

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There's no magic behind it. It was done by non-dimensionalizing the momentum equation in the Navier-Stokes equations. Starting with: $$\frac{\partial u_i}{\partial t} + u_j\frac{\partial u_i}{\partial x_i} = -\frac{1}{\rho}\frac{\partial P}{\partial x_i} + \nu \frac{\partial^2 u_i}{\partial x_i x_j}$$ which is the momentum equation for an incompressible ...

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The way it was explained to me: you start by thinking of all the possible factors that could play in drag (size, velocity, density, viscosity, ...); then you do dimensional analysis and find dimensionless combinations - these tend to be "special" since they remain constant over different scales of time and space. Reynolds number is one such combination. The ...

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In 1897 J. J. Thompson's cathode ray experiments suggested that electrical charges are discrete. Later, the size of the charge was measured in Millikan's famous "oil drop" experiment: http://en.m.wikipedia.org/wiki/Oil_drop_experiment

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The problem is that while mass is the same everywhere on earth, weight is not - it can vary as much as 0.7% from the North Pole (heavy) to the mountains of Peru (light). This is in part caused by the rotation of the earth, and in part by the fact that it is not (quite) a sphere. When you are interested in "how much" of something there is - say, a bag of ...

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Yes. When we use kilograms to measure weight, we are actually referring to $kg_f$ or kilogram-force. http://en.wikipedia.org/wiki/Kilogram-force From Wikipedia: One kilogram-force is equal to the magnitude of the force exerted by one kilogram of mass in a 9.80665 m/s2 gravitational field. In other words, the weight(force) of one kg is equal to one kgf, ...

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He may have been thinking about teaching physics top-down, rather than bottom-up. There is nothing wrong with that. That's exactly what Landau/Lifshitz do in Volume 1 of their "Course of theoretical physics", by introducing a least action principle and deriving much of Newtonian mechanics from it. One could do the same thing for electrodynamics, but the ...

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I found the following quote on the American Institute of Physics website. It is a continuation of Feynman's quote above. I believe it answers your question about his new approach. "When I planned it, I was expected to teach electrodynamics, and then to teach a subject which would really be all the different branches of physics, using the same equation — ...

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