# All Questions

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### How to calculate the time it takes water to travel 100'

100 foot of pipe(lets assume it is straight) Diameter of pipe 2" Flow rate at point of entry into pipe and exit 50gpm Temperature of water 100F 50 psi Or stated another way if I was able to ...
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### How much effect does wind have on cooling an object

I was reading a question on how to cool frying oil on the cooking SE, and in a comment I suggested that having moving air would speed up the cooling as the heat transfer from the oil to the air would ...
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### What would happen, gravitationally, to ships passing by each other at high speeds vs high accelerations?

Consider this scenario: Two identical space ships, the SS Observer and the SS Accelerator. In scenario A, the SS Accelerator is accelerated up to near C, stops accelerating, then flies past the SS ...
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### Physics newton question [on hold]

A woman stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.75 of her regular weight. Calculate the acceleration of the elevator, and ...
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### Mass Hanging From Spring: Potential Energy

I have encountered a problem with a mass m hanging from a spring. I want to find the maximum distance it will be stretched from the spring's equilibrium. At the maximum distance the spring is ...
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### Compression of time in the accelerating universe

In an accelerating universe wouldn't the hours that we lived through yesterday have been a little LONGER than the hours that we are living through today? If everything is speeding up then time is ...
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### What would be seen if a firing laser is accelerated to relativistic speeds then back?

Consider this scenario: Two identical space ships, the SS Observer and the SS Accelerator. Each ship is spherical with a band of mirrored material around the outside and contains a green laser. They ...
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### What happens when two bodies collide in a dynamics point of view?

I'm a high school student learning about energy and momentum. What confuses me is the things with elastic and inelastic collisions. I completely (in my opinion) understand those concepts in energy ...
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### Radiation heat loss and reuse

When the human body lose radiation heat rays, is there a way we can pick it up and collect it? And then use it over again by fex. using a heat exchanger and a device that can emit them (rays) back out ...
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### Thermal Conductivity

I have found an interesting answer for my question in the following link and all what I really want if anyone know a reference that can support this solution. Finding effective thermal conductivity ...
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### Difference between various particle accelerators

What is the difference between betatron, cyclotron, bevatron, synchrotron ?
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### How do i find how long an object can coast for?

I am given the mass of an object (a motorcycle), its velocity, the mass of its wheels, and the radius of the wheels. If the object rolls without slipping, how can I possibly find out how high it can ...
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### 2X2 Matrix from what seems like a scalar

I feel like I just fell off the short bus. I found a problem with a setup like this: "2X2 matrix defined by: $$U=(a_0+i(\sigma \cdot a))/(a_0-i(\sigma\cdot a))$$ where $a$ is a three-dimensional ...
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### Units of Fourier Transform

I am a bit confused about the units of continuous time Fourier transform. Let's say that $x(t)$ is an input signal and has units of volts. Taking the Fourier transform of this yields $X(f)$. I would ...
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So I need some help calculating the convolution of two 1D Greens functions, where the specific formula reads $\int dk G_k(w+i\eta)G_{k+q}(w+i\eta) = \int dk\left[\Im[ ... 0answers 29 views ### How to solve K-G equation with boundary condition? How to solve K-G equation $$\left(\partial^2+m^2\right)\phi=0,$$ with boundary condition $$\phi(t,|\vec{x}|=t>0) =\phi_0.$$ The solution with$t>0$and inside the light cone is ... 1answer 17 views ### Can a wheeled vehicle remain stationary on a water surface? There are many field examples[1] of motorized, wheeled vehicles capable of staying on the surface of water. It appears that the requirement is sufficient "reverse-pressure" against the part of the ... 0answers 30 views ### Differential Geometry uses in physics [on hold] Where do we have differential geometry applications in physics? Just name them and maybe give an example. Also, what are prerequisites to studying it and fully understanding it(i.e. not only the ... 0answers 15 views ### How does GR determine the topology of spacetime? The crux of GR is the action $$S=\int _\mathcal M d^n x \sqrt{|g|}\,R$$ Varying this and setting$\delta S=0$gives you the Einstein field equations. However, that only determines the metric, not ... 0answers 6 views ### Radio wave propagation path loss coefficient below 2? We did a series of measurements of radio wave signal strength. The setup was between stations on top of flat roofs of neighbouring houses (with line of sight). We are interested in the path loss ... 0answers 5 views ###$\rho$-parameters for several Higgs multiplets I'm studying the Higgs mechanism of the spontaneus symmetry breaking in the SM. The expression for the$\rho$-parameter is $$\rho=\frac{M^2_W}{\cos{\theta_w}M^2_Z},$$ that, in the case of a$SU(2)$... 2answers 60 views ### Does it make sense for physics to predict the unphysical? [on hold] I hear people say things like "inside a black hole the laws of physics are not valid" or "there can be parallel universes with different physical laws" or "before the big bang there was nothing". ... 2answers 25 views ### Solar Radiation effects on Earth's orbit Is there enough push from the sun's emissions to push on the earth enough to help sustain orbit. 1answer 43 views ### Maximum Temperature? I have been reading a lot about wavelengths of light and Planck's law and such. Curious as to whether a minimum wavelength of$h$(Planck's Constant) indicates that there is in some way an absolute ... 0answers 31 views ### Transformation of Jaynes-Cummings Hamiltonian This is the Jaynes-Cummings Hamiltonian in the interaction picture:$H_i^n = \hbar g \sqrt{n+1}\begin{pmatrix} 0 & \exp(-i\delta t)\\ \exp(i\delta t) & 0 \end{pmatrix}$I want to transform ... 1answer 39 views ### Is Information Considered Matter? The new internet distribution technology called LiFi is supposed to employ light in the process of transferring internet packets (which are essentially ... 0answers 30 views ### Commutator of Operators So in a spin-orbit interaction there's a hamiltonian and a corresponding perturbation. The spin of the particle is$1/2$. The unperturbed hamilton,$H$, commutes with$L^2, J^2, S^2$. How do you find ... 0answers 17 views ### How to expand the eigenvectors of$J_x$on the basis of$J_z$? Consider a system whose state space is four-dimensional and for which the possible eigenvalues of the operator square of angular momentum$J^2$are$j=0,1$. We can consider then the operator$J_z$and ... 2answers 31 views ### Is it Possible to Burn a fuel (coal especially) without a flame or spark? Actually there was a topic of quality determination of coal where it was heated up to 750-950 degrees in order to burn its mixed volatile substances. I was wondering how coal itself wouldn't burn. ... 0answers 7 views ### Eccentric binary black holes Comparable-mass binary black hole inspirals and mergers are expected to be an important source of gravitational wave signals for current and future ground-based detectors. It is generally expected ... 1answer 25 views ### Is electric potential a field? I'm just learning about electric potential in my second-semester physics class. My textbook is emphasizing the fact that electric potential is a property of the source charges and that I'll soon learn ... 0answers 5 views ### Fourier transform of certain noisy function [migrated] So, I have a noisy signal in time domain,$f(t) = t \eta(t)$where$\eta(t)$is white noise with variance$\sigma$and mean zero, and that it has the property$\langle \eta(t)\eta(t') \rangle = ...
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In the book Principles of Free-electron Lasers by H. P. Freund and T. M. Antonsen, it is written that to get the resonance condition for a free electron laser, we start from ...
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### Tachyons and Lorentz velocity transformation

In general, is it possible to apply the Lorentz velocity transformation to a tachyon? I have tried to do so but the results seemed very illogical. Here's my attempt: suppose an evil spaceship named ...
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### Are deforming force and stress always equal? If they are equal, then why does shape of the body get deformed?

If the deforming force is equal to the restoring force then there is no impact of the deforming force on the body. Then the shape of the body remains constant. How does the body deform, then?
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### Motion of a bullet through a solid block [on hold]

I cannot understand why R=-ma, please can anyone explain me?
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### At what temperature does the vibrational degree of freedom becomes significant for an ideal diatomic molecule?

For ideal diatomic molecules such as $\text{H}_2$, $\text{N}_2$ and $\text{O}_2$, at what temperature does the vibrational degree of freedom significantly contributes to the calculations such as that ...
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### What makes objects fly out of bike basket?

When riding a bike on a bumpy road, objects (let's say, a baseball weighing 150 grams) sometimes fly upwards and out of the basket. However I cannot seem to be able to explain this physically. ...
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### Simple momentum question [on hold]

Question: In pairs figure skating, the heavy muscular male and the petite female skater skate towards each other and come to a stop when the female is lifted. Who undergoes a bigger momentum change? ...
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### Quantum beats and Quantum mechanical side of photosynthesis

I have two questions. One concerning quantum beats alone, another - process of photosynthesis. I am very well aware that there is strong evidence suggesting that mechanism that leads light through, ...
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### Principle behind electrostatic shielding?

If we have a solid conducting sphere with charges around it, then the electric field inside the sphere is zero, otherwise the electrons of the sphere would not be in equilibrium as there would be a ...
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### Gravity goes through everything?

I was thinking about it, the Earth has her gravitational field, but this field comes by the Earth right? Or he just exists around the Earth? If the "gravitons" comes by the Earth, can them goes ...

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