# All Questions

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### Why is the damping force acting on an oscillating system opposite in direction to velocity and not acceleration?

So far I know that the damping force is a frictional force that opposes motion and so it acts in the opposite direction to velocity . Bit why can't the same be said for acceleration doesn't the ...
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### How to calculate temperature of the universe from cosmic microwave background radiation? [on hold]

Two scientists detected the cosmic microwave background radiation at a frequency of 160 GHz. What is the temperature of the universe? So I used the following two equations. peak wavelength x ...
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### Landau Diamagnetism and Pauli paramagnetism

In the conventional definition of Landau's diamagnetism we ignore the effect of spin-electron coupling and vice versa for the derivation of Pauli's paramagnetism. I want to know what would happen if ...
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### What is the relationship between Maxwell-Boltzmann statistics, Boltzmann distribution and Maxwell-Boltzmann distribution? [on hold]

I have recently been studying some statistical thermodynamics and I am currently trying to understand all the different concepts of the course. I was wondering about differences between MB statistics, ...
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### Frictional torque=? [on hold]

A uniform, hollow, cylindrical spool has inside radius $R/2$, outside radius $R$, and mass $M$ (see figure below). It is mounted so that it rotates on a mass less horizontal axle. A mass m is ...
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### What is rotational potential energy?

I don't understand the concept of rotational potential energy. During linear motion, when a force is applied, the work it does gets converted to kinetic energy and there is no change in the ...
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### An ideal black - body at room temperature is thrown into a furnace. It is observed that?

An ideal black - body at room temperature is thrown into a furnace. It is observed that? (A) initially it is the darkest body and at later times the brightest. (B) it is the darkest body at all ...
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### Average speed without given distance [on hold]

Here is the problem where the speed is given but not the distance and need to find the average speed.
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### What would be the masses of the elemental particles if the Higgs field had a different value?

Afaik there is some function, for example, for the mass of the electron $m_e(\phi_1, \phi_2, \phi_3, \phi_4)= ...$, and similarly to the other elemental particles. What is this function?
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### Gravitational force between Earth and Sun is decreasing

According to one of the most famous equations in physics, i.e. $E=mc^2$, the mass of the Sun is decreasing as it emits energy. So there must be some kind of disturbance in planetary orbits, and if ...
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### Functional variation of potential in integral form

I am trying to vary the following action, $$S=\int_{t_0}^{t_1} \text{d}t\,(v^\mu v^\nu g_{\mu\nu} + V(t)) =\int_{t_0}^{t_1}\text{d}t\,(v^\mu v^\nu g_{\mu\nu} + \int_{t_0}^t\text{d}s T_\mu v^\mu)$$ ...
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### Why do Newton's laws hold in a normal and tangential coordinate system?

In my book it says: 'When applying the equations of motions, it is important that the acceleration of a particle be measured with respect to a reference frame that is either fixed or translates with ...
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### General relativity vs graviton discovery

Will the discovery of the graviton lead to the redundancy of general relativity even though it has been so well established. If not, will it mean that gravity will have two separate theories that ...
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### Inversed square law (destroying a hypothetical solar system) [on hold]

Here is my question, say it was possible to have enough antimatter as the explosive of choice to achieve such a feat, and that a black hole isn't formed the magnitude of energy at the origin. How much ...
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### What is the tension on the horizontal rope in this conical pendulum setup? [on hold]

A rope is attached to the top of a straight pole. A person of 890N and a seat of 201 N are attached to the end of this rope. The person rotates 37.4 revolutions/min in the horizontal plane while the ...
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### Potential step and tunnelling

Imagine a particle with energy $E$ heading towards a potential step with height $V_0$ where $E<V_0$. The particle's wave function is oscillatory before the boundary and exponentially decaying in ...
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### Wear rate with sliding speed

I read so many research studying the effects of sliding speed on wear using pin on ring testing machine all of papers said: when the sliding speed increase the wear rate will increase because the true ...
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### Propulsion system

Can a propulsion system be made by facing two air ionizers towards each other, accelerating the ions with fans, and having them repel each other? Would the force generated be greater than just ...
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### Direction of travel in universe

When observe the universe we see that galaxies are much closer than they are at this very moment because of the time it takes for the light to reach us. However do we see this phenomenon in every ...
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### Eigenvalues of spherical harmonics in $d$ dimensions

I'm working on the Schrodinger equation for a hydrogen atom in a $d$-dimensional space, so I'm interested in the possible eigenvalues of the angular momentum part of the $d$-dimensional Laplace ...
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### Charge density on two hemispheres, enclosing a conducting sphere

Two uniformly charged non conducting hemispherical shells each having uniform charge density $\sigma$ and radius $R$ form a complete sphere (not stuck together) and surround a concentric spherical ...
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### Is uniqueness a fundamental property of nature? [on hold]

The Laws of nature are universally applicable and at every point in force. Together they shape our universe but are all "shapes" unique? For example, is it possible that there is a second identical ...
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### triboelectric effect at a liquid-liquid boundary?

In reading up on the triboelectric effect, most experiments deal with solid-solid interfaces. I've found some studies regarding solid-liquid boundaries, and even some engineering manuals outlining the ...
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### What is the refractive index for partially ionized plasma plasma (mixture of electrons ions and atoms)?

I asked a question earlier, why ions are not included in refractive index of plasma . What I do not understand is how a refractive index of plasma can be formed mathematically that is just partially ...
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### How well-defined is the infinite-sheet-of-mass computation?

When computing the gravitational force from an infinite plane (or the electrical field from an infinite sheet of charge), it is standard to begin by making a symmetry argument to say that the ...
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### Projection of a tensor

Consider the following tensor (abstract index notation, e.g. Wald's) $B_{ab}$ and timelike vector field $X^{a}$ such that $X^aX_a=-1$ and $$B_{ab}=\nabla_bX_a$$ Then one ...
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### Why do we integrate in the following derivation? [on hold]

Electric potential due to a point charge. Let a point O have charge $q$ at a distance $x$ from point A and at a distance $r$ from point P ($r<x$). Suppose a test charge $q_1$ is placed at A force ...
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### Can we see interference if move screen? [on hold]

In interference using electrons in double slit experiment, we cannot use light source, as it disturbs apparatus. But, can't we simply move screen towards and away from screen, to know where they ...
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### Uncertainty principle-QM [duplicate]

I some trouble understanding the uncertainty principle. I understand most of the math derivation but not the physics. Is there any intuitive explanation of this idea, and why is the uncertanty does ...
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### (1+1)-General Relativity

Goodevening everyone, my question is: What is the interest of studying the (1+1)dimension General Relativity? Can you explain please? Thank's in advance!
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### Force of water hitting a wall

If you had a 8" pipe with 500psi stream of water exiting it and hitting a wall at 90 degrees 8 feet away, what would the force of the water on the wall be? Thank you all. Non-mathematician.