The definition tag is used in situations where the question is either about how some term or concept is defined or where the validity of an answer depends on a subtle definition of some term or concept used in the question.

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1answer
113 views

Definition of “nonlinear” in the context of perturbation of gravity

What exactly is the definition of a nonlinear perturbation when applied to a background spacetime metric? I have seen so called "linear perturbations" which look like $$ds^2 = -(1+2\Phi)dt^2 ...
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votes
0answers
55 views

The relationship between the two statistical mechanical definitions of entropy

It seems like similar questions have been asked here; hopefully my question is not a duplicate. I am reading my textbook on the statistical mechanical definitions of entropy, and I am very confused ...
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1answer
43 views

Variable definition in wave function for scattering particle?

For the wave function of a scattered particle when finding the scattering aptitude we have: $$\psi(r)=Ae^{ik_0∙r}+\frac{2\mu}{\hbar^2} ∫G(r-r')V(r')\psi(r')d^3r'$$ I was wondering what the variables ...
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0answers
152 views

Streamlines tangent to velocity vector

As from the title, I'm not too sure how they are related. Definition is that streamlines are instantaneously tangential to the velocity vector of the field. Why would a streamline that shows direction ...
0
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1answer
377 views

Definition of “destructive” interference of waves

What is the commonly accepted precise definition of "destructive" interference of waves. Does it mean: interference with complete cancellation or interference where the amplitude gets smaller ...
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votes
2answers
4k views

Exactly how much lift is needed to overcome the weight of an average person?

I am designing a "glider" of sorts, and I have some basic questions about the physics involved to get me started. How much lift is required to overcome the weight of an average person, say 150 pounds? ...
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3answers
448 views

Are we crystals?

Can we say that we are crystals because just like crystals we are made up of very small unit (cell) making up almost the same shape (our body) everywhere.
-1
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1answer
118 views

Is 'grapheme' a substance or a typo?

While reading Ref. 1 I came across the sentence Below we focus on the physics of ideal (single layer) grapheme. I did google search 'grapheme' but the results tended towards a completely ...
-1
votes
1answer
2k views

Definition of the complex wavenumber

My syllabus of electromagnetism defines the complex wavenumber as: $$k = \omega\sqrt{\epsilon\mu}$$ with $\epsilon$ the complex permittivity and $\mu$ the complex permeability. Thus $\epsilon$ and ...
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votes
1answer
64 views

What is difference between 9.8 N (Kgwt) and 9.8 m/s^2 (g)?

What is difference between 9.8 N (Kgwt) and 9.8 m/s^2 (g)? What is difference between kg weight and gravity? I am not so good in physics so please explain in a lot of detail (but sorry for this silly ...
-1
votes
2answers
517 views

What is the difference between the actual distance covered by a projected object and the displacement?

What is the difference between the actual distance covered by a projected object and the displacement? A stone was projected with an angle of projection of 30 and it covered a horizontal distance ...
-1
votes
1answer
62 views

Angular displacement after full rotation

I was wondering is why angular displacement isn't $0$ after $n$ full rotations?
-1
votes
1answer
157 views

Poles, wavefunctions, transmission

Why is it said that $\operatorname{sech}x$ (a transmission amplitude) has a simple pole on the imaginary axis?
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votes
1answer
1k views

When is an object at rest?

When is an object considered to be at rest?
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votes
2answers
125 views

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum?

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum? What is the intuition behind $p=mv$? I had trouble finding any sources that state the actually ...
-2
votes
2answers
180 views

Do physics laws really apply to anything? [closed]

My professor said that a law was stated and announced as a law because it happens in our everyday life. He gave us an example of Newton's 3 laws. He said that walking possess 3 laws of Newton's. Is ...
-2
votes
1answer
69 views

What is the difference between the Lorentz force and the ponderomotive force? [closed]

I understand that Lorentz force is due to motion of moving charged particle in a magnetic field, and I imagine that ponderomotive force is mechanical version analogy to a person surfing on a wave ...
-3
votes
1answer
82 views

Which came first - definition of wave or wave equation? [closed]

In an interview, I was asked to define what a wave is. I replied that it was a sort of disturbance which propagated. Then he asked how I could identify what a wave would be like. I said that the ...
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votes
0answers
43 views

What is infinity? Can we define it? [closed]

We talk about infinity very frequently, but what is exactly infinity, what is its definition? I have thought about it, researched about it, and also studied its laws. But they aren't just making any ...