# All Questions

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### Delta wing flow patterns (straight and yawing)

I was wondering the differences between fluid patterns and their consequences when a delta wing is straight and yawed slightly.
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### Can we deviate a bullet from its target? Did anybody try this?

Can we deviate a bullet from its target? Means by applying any strong field at the target? Is there any technique so far like this!
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### What are the “other” Hadamard matrices?

The Pauli matrices $$X = \begin{pmatrix}0&1\\1&0\end{pmatrix}, Y=\begin{pmatrix}0&-i\\i &0\end{pmatrix},\,\text{and}\, Z=\begin{pmatrix}1&0\\0&-1\end{pmatrix}$$ can be used ...
102 views

### What does traveling close to speed of light mean?

This has been bugging me for a while. We all know in relativity that if you travel close to speed of light, all sorts of crazy things happen. But what does it mean to travel close to speed of light? ...
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### 2 spheres both negative or positive [closed]

Two small charged metal spheres A and B are situated in a vacuum. The distance between the centres of the spheres is 12.0 cm, as shown in Fig. 4.1. The charge on each sphere may be assumed to be a ...
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### Are the laws of physics bound by the same performance bounds algorithms are bound by?

Consider the problem of finding the convex hull for $n$ points on a plane. No constant time algorithms exist to solve it. Now say you represent the points as poles of equal height that you hammer ...
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### Intuition on positive-operator valued measures (POVM)

I'm having a little trouble understanding what positive-operator valued measure (POVM) are- in particular why/how they are non-negative. For instance, if they just represent measurements, what about ...
144 views

### Uses of Static Electricity

Is it possible to store static electricity in any type of battery and can they be used in electric appliances(light,bulbs mainly)?
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### Is a gapless system always conducting and a gapped system insulating?

In an answer to this question, @user566 mentioned that there is a qualitative difference between gapped and gapless systems; that gapless systems are conducting and gapped system are insulating. Is ...
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### Magnetic field of a living human [duplicate]

Is it true that a human body is like a bar magnet? Say our head is north pole while the legs are south pole, or vice versa? If so, can we confirm it by experiment say with the 360 Pro compass etc?
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Say we have a non-uniform magnetic field that is static in time. Specifically, let's make it: $\overrightarrow{B}(x,y,z) = x \hat{z}$ Now say we have a metal loop in the xy plane which has a non-...
124 views

### if light is electromagnetic then can light produce electricity or attract metals

what I mean to say is that if light is electromagnetic in nature then shouldn't it show electric or magnetic properties on matters? Like if light falls on a metal it should produce current due to ...
621 views

### Violation of the second law of thermodynamics? [closed]

Here is a machine which seems to violate the second law of thermodynamics: $A$ and $B$ are point black bodies of the same temperature (initially). everything is rotationally symmetric around the ...
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### Hysteresis in liquid–solid-phase transitions such as Agar

I'm wondering how it is possible for a substance to have a significantly different melting point than its freezing point. What physical interaction "locks" a substance such as Agar into the phase that ...
308 views

### What are the 'types' of parametric down conversion?

I'm looking at photon entanglement, and everywhere in the literature there's a reference to 'type-II' parametric down conversion as a source of entangled photon pairs. I know what parametric down ...
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I am reading quantum mechanics from Shankar's Principles of Quantum Mechanics. On page 157 he defines the box potential $V(x)$ as V(x) = \left\{ \begin{array}{rl} 0 &\mbox{ if |x|< L/2} \\... 0answers 50 views ### Relative time/space - Two clock thought experiment [duplicate] Please pardon my english. Here is my simple thought experiment. ... 1answer 83 views ### Hydrogen bond and van der Waals bond Just now I am studying about hydrogen bond and van der waals bond. I understand and able to differentiate between them but thinking of the similarities, do they have any? 1answer 100 views ### Determine eigeinvalue and eigenvector of two operators R and L [closed] Question: Let H be a Hilbert space with countable-infinite orthonormal basis {|n>}_{n \in N}. The two operators R and L on H are defined by their action on the basis elements \begin{align} R|n\... 1answer 87 views ### How can an electron be fired at a target when uncertainty principle says it will spread out around axis of motion? Consider an electron fired at a target. Taking the axis of motion to be x, and position to be (x,y,z) then \Delta y = \Delta z = 0 Therefore by the uncertainty principle \Delta p_y = \... 1answer 3k views ### Instantaneous axis of rotation and rolling cone motion Suppose a cone is purely rolling (no slipping) around a fixed axis. I mean, it is revolving around a fixed axis perpendicular to the ground and passing through its vertex and also rotating, so the ... 2answers 86 views ### Newtonian potential defines size of Universe? As I understand it the Newtonian potential \Phi at the position of an observer in space is approximately given by:\Phi \sim \frac{G M}{R}, where $R$ is the radius of a sphere centered at the ...
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I have two rods with lengths $L_1$ and $L_2$, connected with a joint in the middle and I would like to express the moment(torque) around a point mass (P) at the far end of rod 1. The relation between ...
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### How can there be current if all paths have same potential difference

I am learning about circuit analysis now, but there is something that I can't wrap my head around. Imagine this simple circuit: ...
2k views

### How can energy be useful when it is 'abstract'?

The topic which haunted me for two years until I gave up on it. But now I am doing engineering and this topic suddenly popped out of my textbook from nowhere. I seriously need to understand this topic ...
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### Why in series combination of circuit has same amount of current flow in every conductor? [duplicate]

Why in series combination of circuit has same amount of current flow in every conductor? Whereas in parallel combination the amount of voltage is same?
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### Clarification about Bragg's law explanation

The Wikipedia has this illustration of Bragg's law and then says The two separate waves will arrive at a point with the same phase, and hence undergo constructive interference, if and only if ...
123 views

### Standing waves on a compound string

I've been having some difficulties in understanding standing waves. The questions that I have are as follows: 1) Suppose I have a compound string, made up of two strings. What is the correct way to ...