Top new questions this week:
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An even number of books (say four) are held in the manner shown in the figure. It is obvious that if we apply a large force inwards, we can increase the normal force, and hence the friction which ...
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Defining "stable orbit" between two bodies as one where, in the absence of other bodies or non-gravitational forces, the distance stays between some value pair $r_{min}>0$ and $r_{max}$. ...
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I would like help in understanding something that has been causing me a lot of trouble recently: Why is energy always related to time in physics?
Examples include the 4-momentum, the energy-time ...
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Should one have the windows open or closed when a tornado is nearby? B.S. in Physics but very rusty in this day and age. I have always been taught that one should keep windows cracked open because of ...
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The Sun has a peak wavelength of around 500 nm and an effective surface temperature of 5770 K, and sunlight cannot be focused to make something hotter than the Sun, because this would be heat flowing ...
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I am self-studying the book "Quantum field theory and the standard model" by Schwartz, and I am really confused about the derivation of the Photon propagator on page 128-129.
He starts ...
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In Fundamentals of Many-body Physics by W. Nolting, 1e, the author arrives at the following formula for the electron-electron contribution to the Hamiltonian of Jellium:
$$
\hat{\mathcal{H}}_{ee}=\...
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Greatest hits from previous weeks:
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I was reading somewhere about a really cheap way of travelling: using balloons to get ourselves away from the surface of the earth. The idea held that because the earth rotates, we should be able to ...
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During breakfast with my colleagues, a question popped into my head:
What is the fastest method to cool a cup of coffee, if your only available instrument is a spoon?
A qualitative answer would be ...
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Suppose we have two events $(x_1,y_1,z_1,t_1)$ and $(x_2,y_2,z_2,t_2)$. Then we can define
$$\Delta s^2 = -(c\Delta t)^2 + \Delta x^2 + \Delta y^2 + \Delta z^2,$$
which is called the spacetime ...
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Why doesn't the Moon fall onto the Earth? For that matter, why doesn't anything rotating a larger body ever fall onto the larger body?
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Consider two blocks, one on top of the other on a frictionless table, with masses $m_1$ and $m_2$ respectively. There is appreciable friction between the blocks, with coefficients $\mu_s$ and $\mu_k$ ...
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As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects ...
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This comes from a brain teaser but I'm not sure I can solve it:
You are in a rowing boat on a lake. A large heavy rock is also in the boat. You heave the rock overboard. It sinks to the bottom of ...
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Can you answer these questions?
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I am trying to reproduce the equivalent photon approximation as discussed in chapter 17.5 in Peskin and Schroeder but cannot justify equation (17.93).
The process we are considering is the scattering ...
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Bell inequalities can be discussed in the language of geometry. In papers such as [1], there is a general flow of definitions leading to the geometric picture of Bell inequalities:
$$\text{Behaviors} \...
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I have a basic question about a few calculations involving the quantum mechanical Laplace-Runge-Lenz vector.
In classical mechanics there is the Laplace-Runge-Lenz vector, which for a hydrogen-like ...
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