0
votes
1answer
158 views
Deceleration of Vehicle off pavement
How would I calculate the deceleration of a vehicle (ATV), wheels locked, on dirt? How long would it take to halt? How fast is it decelerating?
I used this calculator, but it seems incorrect for a ...
1
vote
2answers
22 views
Electric potential energy after nuclear fission
We have a uranium-236 nucleus that fissions into two equal fragments, and I'm supposed to find the electrical potential energy just as the two fragments split apart. No other information is provided.
...
7
votes
5answers
103 views
Physical representation of volume to surface area
I was looking at this XKCD what-if question (the gas mileage part), and started to wonder about the concept of unit cancellation. If we have a shape and try to figure out the ratio between the volume ...
0
votes
0answers
9 views
How does tension apply torque on a pulley?
How is tension in a string able to apply torque on a string? How does string itself able to apply a force on pulley? What is happening inside the pulley?
The pulley has a mass m and is a disc .
2
votes
2answers
19 views
Does the expansion of the universe soon after the Big Bang affect the amount of time that light takes to reach us?
If faster than light travel is impossible, how is it that light emitted from matter so close together in the time soon after the Big Bang is only now just reaching us? I would assume that there would ...
2
votes
1answer
65 views
Convert a 200mm linear stroke into 90 degrees motion
Can anyone help me Convert a 200 mm linear stroke into 90 degrees motion with as much mechanical advantage as possible or into two 90 degrees motions with as much mechanical advantage as possible?
...
0
votes
0answers
15 views
A Calorimetry Problem
I have a question in calorimetry from an old competitive exam. The question is:
The temperature of $100$ grams of water is to be raised from $24 ^\circ$C to $90 ^\circ$C by adding steam to it. ...
3
votes
1answer
97 views
Inflation and scalar spectral index
I've been reading that the results from the Planck satellite constrain a number called the "scalar spectral index" to be 0.96 rather than 1 at the 5-sigma level.
This is supposed to be big news, but ...
0
votes
0answers
20 views
What values should the solved time-independent Schrodinger equation return?
I'm doing a project on Schrodinger's equation for my differential equations class. We solved the time independent function, and now we want to provide some examples of applying the equation by solving ...
-2
votes
0answers
23 views
If air contains oxygen and nitrogen, why won't these two elements form water? [closed]
If air contains oxygen and nitrogen, why won't these two elements form water?
Shouldn't these two elements react and form water? Why do they stay seperated?
2
votes
2answers
52 views
Question about the proof that heat capacity goes to zero if temperature approaches $0K$
I don't completely understand the proof that is given for the claim that the heat capacity goes to zero, if the temperature approaches $0K$.
They do it as follows, if $C_x$ is the heat capacity where ...
0
votes
1answer
17 views
Doubt in problem regarding resistance a of cylinder
I've been working on some exercises and I'm in doubt if my procedure with this one is correct. We have a hollow cylinder with internal radius $r_a$, external radius $r_b$, resistivity $\rho$ and ...
2
votes
1answer
36 views
Questions about the Jeans length
I have a couple of questions about the Jeans length. Suppose the universe has a homogeneous energy density, except there's a spherical region that is overdense.
I understand that if the region is ...
2
votes
1answer
29 views
Is there a one-to-one relationship between colour theories and our trichromatic vision?
This has started to bug me more and more… it involves:
colour theory
the trichromatic properties of our eyes through cone cells
and light.
Is there a one-to-one relationship between colour ...
2
votes
2answers
21 views
How would a change in ambient temp affect a radiator?
I'm curious if you have a radiator or say a block of metal (lets say it's copper since it has the highest thermal conductivity) and on one side is a processor producing heat.
At idle the processor ...
1
vote
0answers
17 views
rate of flow out of a reservoir
A reservoir contains a fluid, and there is an aperture at the bottom through which the fluid flows out as shown in the illustration:
I understand that the rate of flow is based on at least these ...
1
vote
2answers
92 views
What is the pressure on an empty pneumatic tube?
At the residence I'm constructing a kitchen digester. The gas is to be collected into an old bicycle/scooter tube - initially as empty as may be after wringing it out..
Will the digester (total ...
1
vote
1answer
69 views
Why is this not a realisable operation on a quantum system?
Let $\rho = \begin{bmatrix}\ 1&0 \\ 0&0 \end{bmatrix}$, $\rho' = \begin{bmatrix}\ 0&0 \\ 0&1 \end{bmatrix}$, $\rho'' = \dfrac{1}{2}\begin{bmatrix}\ 1&1 \\ 1&1 \end{bmatrix}$ ...
0
votes
0answers
20 views
Scalar-fermion bound state
Is it possible to have a bound state between a scalar and a fermion? For example, a squark--anti-squark bound state, provided that the decay width is sufficiently small compared to the binding energy?
...
3
votes
1answer
42 views
The etymology of “Umbrella Sampling”
I am just wondering where the term Umbrella Sampling came from. Is there another meaning of literal "umbrella" in physics or mathematics?
0
votes
2answers
42 views
About the electrostatic voltage
What's the difference between electrostatic voltage and normal voltage, like the battery's voltage.
How to calculate the charge on a charged plate if we knew its electrostatic voltage?
2
votes
1answer
52 views
Manufacturing Fresnel Lenses with Sound
I understand fresnel lenses are manufactured using CNC machines. I was wondering, if it would be possible to use sound to vibrate liquid silicon and then fast cool it into the standard form of a ...
0
votes
1answer
55 views
Derivation of Dirac equation using the Lagrangian density for Dirac field
How can I find Dirac equation using the Lagrangian density for Dirac field?
3
votes
0answers
42 views
Lattice model completely constrained by boundary data
I am dealing with a lattice model that has the peculiar property that if I specify all the spins on the boundary, by local conservation laws, the whole lattice configuration (throughout the whole ...
2
votes
4answers
189 views
How do we know that there isn't a classical solution to the measurement problem/Quantum Mechanical uncertainty?
It was mentioned to me that it can be shown that there is no classical explanation for the uncertainty in Quantum Mechanics -- i.e. that there are no hidden workings that we have just not yet seen, ...
2
votes
1answer
21 views
Does increasing the pressure of the gas in a container by pumping gas into it increase temperature?
Basis is the ideal gas law: http://en.wikipedia.org/wiki/Ideal_gas_law
This law only states a mathematical relationship between many variables. It does not state what happens if one of the variables ...
0
votes
1answer
116 views
Applying Gauss' Law to find Electric Field
I'm in doubt in the application of Gauss' Law to find electric fields when the charge distribution is symmetric. Well, first of all: I know how to find the magnitude of the field - we just enclose the ...
1
vote
1answer
87 views
neutron transport approximations for nuclear rocket modelling
I'm pretty ignorant regarding neutron and nuclear transport modelling, but i'm interested in trying to pursue it for a particular pet project. It regards modelling of nuclear reactions like those ...
3
votes
3answers
730 views
Gravitational time dilation at the earth's center
I would like to know what happens with time dilation (relative to surface) at earth's center .
There is a way to calculate it?
Is time going faster at center of earth?
I've made other questions ...
10
votes
2answers
113 views
When are there enough Casimirs?
I know that a Casimir for a Lie algebra $\mathfrak{g}$ is a central element of the universal enveloping algebra. For example in $\mathfrak{so}(3)$ the generators are the angular momentum operators ...
0
votes
2answers
39 views
Kinetic energy of two charged balls at infinite distance between them
If I have two balls with masses and charges $m_1, q_1^{+}$, $m_2, q_2^{+}$, initially held at distance $d$, and then released, how can I know the kinetic energies of each of the balls at infinite ...
3
votes
3answers
61 views
If light rays obey to the wave equation, why can they be thought as straight lines?
I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object ...
-2
votes
0answers
44 views
What is the state of contempoary Quantum Physics as a discipline? [closed]
Sometimes I take the time to read textbooks and go to talks about Quantum Physics. Most of the time I do that I am appalled at how... Badly people seem to understand QM.
I do not have formal ...
1
vote
0answers
15 views
Leap from photon gas energy distribution to black body radiation?
I remember considering in class in college, the case of a photon gas trapped in a d-dimensional box as a subject of interest, whose energy distribution, heat capacity, etc. should be calculated.
...
0
votes
3answers
271 views
A man running on the treadmill
Imagine a man is running on a treadmill. His inertia with respect to floor will be zero because he is not moving with respect to floor. If both he and the tread mill suddenly stops he will not fall, ...
2
votes
1answer
30 views
Escape velocity for hydrogen molecules
The question:
At what temperature is the RMS speed of Hydrogen molecules equal to the escape speed from the earth's surface? Values of radius of earth($r$) and gas constant $R$ has been supplied ...
1
vote
0answers
25 views
Solar sail area going to Proxima Centari [closed]
I have a physics question that I need some help with:
"Proxima Centauri is a star in the Alpha Centauri solar system, it’s the
nearest star to our sun (4.24light−years) ...
1
vote
1answer
63 views
What is the general statistical definition of temperature?
Temperature in an isolated system is defined as:
$$\frac{1}{T} = -\frac{\partial{S(E,V,N)}}{\partial{E}} $$
But I wonder how one can generalize this to a random system.
Or for instance to a point in ...
2
votes
1answer
81 views
How to find the Higgs coupling with a mixing matrix?
It is known that the couplings to the Higgs are proportional to the mass for fermions;
$$g_{hff}=\frac{M_f}{v}$$
where $v$ is the VEV of the Higgs field. I'm trying to figure out why this is true ...
1
vote
1answer
54 views
Arbitrary tensor covariant derivative
what are the rules for performing covariant derivatives on tensors of arbitrary rank?
I found a few examples of Tensor derivatives:
$$\nabla_{c} T^a {}_{b} = \partial_{c}T^a {}_{b}+ \Gamma^a{}_{cd} ...
10
votes
2answers
144 views
How large can planets or moons appear?
In many artistic impressions or movies there are pictures or scenes where the sky is filled with an enormous moon (as seen from a planet) or vice versa.
I wonder if there is an upper limit to the ...
0
votes
0answers
5 views
Why is it difficult to numerically solve multi-electron time-dependent Schrodinger's equation [migrated]
It seems that people usually use the Single Active Electron (SAE) approximation to deal with a multi-electron system, transforming the problem into a single electron problem. For example, in ...
3
votes
1answer
97 views
How to determine predicted CP violation for a given SUSY point?
I'm currently studying at the spectra of some supersymmetric models, and would like to know whether the parameter points I'm looking at are ruled out due to excessive CP violation.
I am using SPheno, ...
0
votes
1answer
27 views
Isothermal Gas Expansion, a Reversible or Irreversible process?
Consider the following situation. A certain quantity of ideal monatomic gas (say one mole) is confined in a cylinder by a piston and is maintained at constant temperature (say $T_0$) by thermal ...
1
vote
0answers
21 views
Induced current using a reference system bound with a moving charge
Let's suppose to have a charge moving at velocity $\textbf{v}$ and a square wire.
If I choose a reference system bound with the square wire, since the charge is moving at velocity $\textbf{v}$, in ...
1
vote
2answers
87 views
Can we measure “wavefunction” of quantum particles?
We know that there is uncertainty principle, so question: can we ever measure wavefunction of particles? I do not think this is possible, but I am not sure. I guess that everything is probabilistic. ...
4
votes
1answer
122 views
Noether's identities
I have some questions about the Noether's second theorem (generally not covered by field theory books):
What is the most general Noether identity for (classical) field theories?
Why are Noether ...
0
votes
0answers
21 views
Black hole and photons [duplicate]
I've read in a book that even light can't escape the gravitational pull of a black hole after a certain distance. But this seemed impossible to me.
Imagine a photon, moving directly in the opposite ...
-1
votes
1answer
47 views
Convert units from cal cm^-1 day^-1. to Wm-2
I am trying to calculate the energy budget of a water body and the last term I'm trying to calculate is the energy advected from the water body ($Q_v$). This equation is given by:
$Q_v = V ( (T_1 - ...
1
vote
1answer
59 views
Friction on a conveyor belt
I was surfing through an Olympiad paper and I was caught with this question.
A block of mass 1 kg is stationary with respect to a conveyor belt that is accelerating with $1\, \tfrac{m}{s^2}$ ...
