10
votes
2answers
553 views

Long time deviations from exponential decay in radioactivity

Are there any examples of common substances whose decay is not exponential? We're used to thinking about radioactivity in terms of half-lives. This is a concept that makes sense only for a decay that ...
-1
votes
0answers
3 views

how to convert 1atm to kj/m3

i am trying solve similar questikn like this myweb.loras.edu/cm418218/EGR334/HW%2019%20Solutions%20Spring%202012.docx 13th slide but in si unit thanks
0
votes
0answers
3 views

Can an arrangement of particles be duplicated precisly?

Is it possible to teleport or clone someone or something? After watching this TED talk by Max Tegmark - https://www.youtube.com/watch?v=GzCvlFRISIM I find myself wondering if it is then possible to ...
0
votes
0answers
7 views

How can light travel at speed of light?

I am well aware that the speed of light is a universal constant at which nothing but light can travel. But why? Why can even light travel at such a speed? Our maths tell us that anything with rest ...
0
votes
0answers
19 views

Can you please tell me what's wrong with my calculation? [on hold]

I'm taking second level physics at the university. Here's an exercise I've been working on and wasn't able to get the right answer for: In the figure take $q_{1} = 69μC$ , $q_{2} = -32μC$ , and ...
0
votes
0answers
9 views

Can someone explain effects of time dilation on expansion of universe

I'm not a physics guy, but this is something I have always wondered about. If a clock flown by an object of high mass runs slower, what is the effect of this in regards to the density of the universe. ...
0
votes
1answer
9 views

World-sheet energy-momentum tensor and OPE

On p43 of Polchinski's book, it says that under the world-sheet translation $\sigma^a\rightarrow\sigma^a+\epsilon v^a$, $X^\mu\rightarrow X^\mu-\epsilon v^a\partial_a X^\mu$. And $$j^a=iv^b T_{ab},$$ ...
1
vote
1answer
12 views

What exactly happens to an exposed human body in space?

I know that space is a vacuum, has no air and is very, very cold. from what i have seen in movies and TV shows when a space suit is exposed the oxygen will escape will escape like a visible gas and ...
15
votes
15answers
2k views

What are the mechanics by which Time Dilation and Length Contraction occur?

What are the mechanics of time dilation and length contraction? Going beyond the mathematical equations involving light and the "speed limit of the universe", what is observed is merely a phenomenon ...
3
votes
2answers
343 views

Does a current-carrying wire running through the centre of a solenoid experience force?

Imagine looking at a solenoid from above. Current passing is through it in a clockwise direction. The direction of the field lines therefore is towards the bottom of the solenoid. Now pass a straight ...
-1
votes
0answers
11 views

Algorithm of Patankar for Numerical Heat Transfer and Fluid Flow [on hold]

I look for the algorithm of Patankar (for exemple: SIMPLE, SIMPLER, ...
3
votes
2answers
59 views

Circular motion and time dilation

Einsteins' time paradox was shown when two atomic clocks were synchronized and one was sent in a super sonic plane and the other kept at rest. When the two where then checked it was shown that yes ...
0
votes
2answers
2k views

Realistic calculation of heat loss for pipe

Good day everyone, I am new on this site and I hope to find here help, since I am not going anywhere with the literature I have found. I try to calculate realistically the heat loss of a hot, ...
1
vote
1answer
48 views

What would happen if a bowling ball near absolute zero suddenly appeared in my room?

How cold would the room get? Would I die? My initial estimation is that it one bowling ball at 0K (i.e., 300K below room temperature) would have about the same effect as 10 bowling balls at 270K ...
4
votes
6answers
760 views

Could the Schrödinger equation be nonlinear?

Is there any specific reasons why so few consider the possibility that there might be something underlying the Schrödinger equation which is nonlinear? For instance, can't quantum gravity (QG) be ...
0
votes
0answers
16 views

Minkowski spacetime vs Euclidian space

Two questions marked in bold: What is the magnitude of a Minkowski spacetime four vector? I'm deducing that it is c for all observers, and that it is a velocity vector. In Euclidian space, a ...
2
votes
2answers
127 views

Disconnected aileron/surface deflection in terms of speed?

Would a disconnected surface, especially aileron, deflect upwards as you slow down due to increased alpha? I figure out it is more likely to deflect upwards as you increase your airspeed, thus having ...
3
votes
2answers
208 views

Misaligned Mirror on Michelson Inferometer

If one of the outer mirrors on a Michelson interferometer was to be misaligned by a small angle of theta, what would be the shape of the interference pattern in the detector plane? What would happen ...
0
votes
1answer
42 views

Microscopic understanding of Brewster angle

The textbook explanation is that, at Brewster's angle, the electric dipoles excited by the incident light can't reradiate to the reflection direction since it's aligned with the dipole moments. Is ...
1
vote
2answers
303 views

Circularly polarized light incident at Brewster's Angle

If a perfectly circularly polarized wave of light is incident on a dielectric medium (coming from air) at Brewster's Angle, what will the polarization state of the transmitted wave be? I am aware ...
0
votes
0answers
6 views

Convention about delta x in Waves Interference

http://imgur.com/oxFF7q8 They seem to adopt a convention that delta x must always be positive. Otherwise, there is no way to know what the phase difference of the sources actually means. Does a ...
0
votes
1answer
37 views

Would equations for a spinning top be an (x,y,z) vector

I am following the equations on this page, and for torque it is $mgr\sin\theta$, but I am curious about $r$. I am working on a game and I want to correctly model the top, and am curious if $r$ should ...
0
votes
1answer
20 views

Reflected waves and phase changes

If a wave passes from a lightweight string to a higher density string, we say that the reflected wave has a pi phase change. Can we say that it has minus pi phase change? If yes, why would that not ...
4
votes
1answer
168 views

Pipe in a flowing river problem

I'm working on a certain problem in fluid mechanics, which isn't really my strongest area. The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing ...
6
votes
2answers
76 views

How quickly should a fluid come to hydrostatic equilibrium?

Let's say I'm holding a one-liter water bottle, full of water, which I then drop. Before dropping the water bottle, the equilibrium is for there to be a pressure gradient in the water canceling the ...
1
vote
0answers
17 views

Supergravity solution, metric for the total space, and connection

In supergravity solutions, one sometimes encounters the case where the manifold may be a bundle over some base space, and one has to write down the explicit metric regarding such bundle. I would like ...
1
vote
1answer
39 views

Refractive index of dielectric in different frames of reference

The setup A transparent isotropic dielectric medium moving in the negative $x'$ direction at speed $v$ in frame $S'$ is stationary in frame $S$, where it has refractive index $n$. In other words, ...
12
votes
2answers
254 views

Holographic Renormalization in non-AdS/non-CFT

In AdS/CFT, the story of renormalization has an elegant gravity dual. Regularizing the theory is done by putting a cutoff near the conformal boundary of AdS space, and renormalization is done by ...
2
votes
1answer
26 views

Bulk-boundary cutoffs in AdS/CFT

I'm studying the holographic entanglement entropy (HEE) in this paper (Ryu-Takayanagi, 2006). In section 6.3 they compute the HEE for a segment in a 2D CFT. To do so, they obtain the corresponding ...
1
vote
1answer
42 views

Rotation speed measurment

Could anyone please explain with simply how we can measure the rotation speed of an object using the Sagnac Interferometer ?
5
votes
2answers
266 views

Speed of light in general relativity

My question has a few parts concerning the speed of light in general relativity. Firstly, time changes in response to gravity and speed. Therefore, as gravity effects time in an area of space, should ...
1
vote
3answers
56 views

internal conversion and the electromagnetic force

I have read that the mechanism behind internal conversion, in which a nuclear transition leads to the ejection of an electron in one of the lower atomic orbitals, is related to the fact that the ...
2
votes
1answer
36 views

Rate of change of a normalised wave function

I'm reading Weinberg's Lectures on QM. On top of p23 it says $$i\hbar\frac{d}{dt}\int|\psi(x,t)|^2d^3x=i\hbar\int\psi^*(x,t)\frac{\partial}{\partial ...
0
votes
1answer
57 views

Heat flow in a hollow cylinder

Consider a hollow cylinder of different outer radius and inner radius and two different temperatures are maintained at the outer and inner surfaces such that inner temperature is higher. Because of ...
2
votes
1answer
59 views

How to weigh your nephew [on hold]

My nephew is 3 and weighs around 30 pounds I am guessing. However, I would like to weigh him at home. I have kitchen scales, one flat one that goes up 1kg and one that looks like this picture that ...
2
votes
2answers
75 views

How to understand the indeterminate process in thermodynamics?

Consider a closed composite system with an internal movable adiabatic wall. If we release the piston, thermodynamics cannot determine the final equilibrium state (the temperature cannot be ...
0
votes
0answers
24 views

Calculation of frequency from known beat pattern

< Why is the answer 498 Hz and not 502 Hz? The difference between the two frequency is 2.
3
votes
1answer
192 views

Does dark energy annihilate energy?

Antimatter and matter particles annihilate. But does dark energy annihilate energy? We consider energy to be photons, and such, correct? So when we say energy, we're actually talking about some ...
0
votes
2answers
37 views

Tachyonic field

i'm working on a paper about symmetron cosmology. symmetron is a scalar field that by its symmetry breaking can explain the dark energy. the action is: ans A , V are assumed to be: where M ...
6
votes
2answers
274 views

Escape velocity

I have several confusions regarding escape velocity. I am sure I am missing something(s) obvious or maybe I am taught wrong. Lets say we throw an object of any mass at exactly escape velocity of ...
2
votes
1answer
50 views

Relationship between Connection and Material Derivative

Suppose $D\subset \Bbb R^3$ contains a fluid and that $f : D\times \mathbb{R}\to \mathbb{R}$ is a time dependent function defined on the fluid region. In that case, the material derivative is defined ...
0
votes
0answers
67 views

How many atoms make up the average ant? [on hold]

Given an ant is anywhere from three to five milligrams. This wasn't homework but I figured it out. I believe it is five quintillion.
0
votes
1answer
32 views

Would days be longer as the polar ice caps melt? [duplicate]

I got question in my mind striking for several days but not able to prove it, suppose polar ice on earth melt, would the days be longer? My friend said it was due to moment of inertia of the earth ...
1
vote
1answer
83 views

How far do atoms move in a wire when whirling it horizontally?

so the question is: I whirl a mass m attached to a wire with length L and diameter d around my head in the horizontal plane. The mass takes t seconds to move around a circle. How far do the ...
1
vote
2answers
131 views

Inner products with orthonormal bases

Probably a stupid question here - I think it's a case of me not having sufficient mathematical background to follow this through. In Leonard Susskind's Theoretical Minimum book, he represents the ...
3
votes
0answers
33 views

Bound states in 1D & 2D

Why does Mother Nature allow bound states in arbitrarily weak attractive potential in 2D but not in 3D? See, for example, this article: ...
3
votes
1answer
72 views

Help with 1D and 2D density of states

I am currently looking at changes in DOS when sampling recipocal space finely. More precisely, I am looking at the expressions $$\rho_\text{1D}(E)\text{d}E = \frac{m}{\pi \hbar} \sum_i ...
0
votes
1answer
9 views

Intense of liner polarized wave: with a polarizer vs. without a polarizer differences

We had this experiment in which we measured the intense of linear polarized wave - with and without a polarizer. I noticed that without the polarizer the intense was slightly lower than with the ...
0
votes
2answers
23 views

How are heat transfer rate and heat capacity constant of a material related?

How are heat transfer rate and heat capacity of a given material is related? When I was a kid I imagined it like "Capacity is like a container or bucket of some sort, if it gets filled easily it can ...
12
votes
4answers
2k views

Why is there a controversy on whether mass increases with speed?

Some people say that mass increases with speed, some people say that the mass of an object is independent of its speed. I understand how some (though not many) things in physics are a matter of ...

15 30 50 per page