# Questions tagged [definition]

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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### Difference b/w Kinetics & Kinematics w/concrete example

(I know whether I understand this or not doesn't matter much to my work & study but am just curious.) I still can't differentiate in my head kinetics and kinematics (similar thread is found but ...
215 views

### Difference between a vector field and a force field

In mathematics while learning about vector fields, we define a "vector field" as "a function of space whose value at each point is a vector quantity". That is, at each point in space there is a vector ...
158 views

### What is the definition of “force” in quantum field theory?

In quantum field theory, there are certain interactions that we seem to associate with the action of "forces." For example, the exchange of a gauge boson between two matter particles is associated ...
525 views

### Why is voltage described as potential energy per charge?

Voltage is often called an electromotive force since it causes a flow of charge. However, it is described in terms of Joules per Coulomb or Potential Energy per Charge. Question: How does the ...
947 views

### Is there a definition of force? [duplicate]

Well, Newton's three laws talks about forces, but no definition is given. In truth, Newton's second law gives an idea of what total force is: the time change rate of momentum. But, if we have a force ...
7k views

### What is the definition of linear momentum?

Every where and book I search I get that the definition of linear momentum is the amount of speed (quantity of motion) contained in it or simply it is mass $\times$velocity? So, what is an ...
148 views

### Thermodynamics second law variational statement query

In thermodynamics as I understand entropy is a state function. A state function is a property whose value does not depend on the path taken to reach that specific value. In contrast, functions that ...
145 views

### How to interpret this construction of the states in QFT?

Non-Relativistic Quantum Mechanics To make this question clear it might be useful to contrast with non-relativistic quantum mechanics. In any quantum theory, the states of a system are unit rays in ...
93 views

### What orbit does a planet have to have to be a planet? [closed]

Other questions have dealt with where you could find a planet-like object, and what a planet has to consist of to count as a planet. But this question is directed as what orbit or path an object would ...
1k views

### The definition of mutual capacitance

I am not sure I completely understand the definition of mutual capacitance. Let's say we have two conductors, $A$ and $B$, so that the following holds: Both conductors are isolated. $A$ is isolated ...
4k views

### What is meant by potential energy for a particle in a field?

Potential energy is usually defined using a field and a particle that experiences the field force, as the work down in moving a unit particle from infinity to a position in that field. But some ...
2k views

### Why is the absolute zero a rational number in Celcius?

From the question "Why is the absolute zero -273.15ºC?" I understood that 1°C is the 100th part of the difference of melting and boiling temperature of water (this is my high school physics, ...
2k views

### Confusion between two different definitions of work?

I'm doing physics at high school for the first time this year. My teacher asked us this question: if a box is slowly raised from the ground to 1m, how much work was done? (the system is only the box) ...
194 views

### Will the SI units need redefining ever again?

Up until recently, there were obvious problems with the SI definitions of fundamental units, like bits rubbing off the kilogram prototypes (or mercury vapour absorption), and the water used for the ...
355 views

### Is a singularity a real thing?

I've heard the work a few times now, the most recent in the star trek film. Is a singularity a real thing? If so what is it?
1k views

### Centre of Mass vs. Centre of Gravity [duplicate]

I want an explanation for this: "The centre of mass & centre of gravity of an extended body on the surface of earth is different for objects with sizes greater than 100m" As a matter of fact I ...
5k views

### What is the third cosmic velocity?

I have been studying Gravitation chapter and there I found one term: Third cosmic velocity which is also known as interstellar speed. So what is it? What it really tells about? I tried to gather some ...
11k views

### How can you tell if the work done by a force is negative?

This is kind of confusing to me. I'm guessing that it's specific to the problem. Is the work done by friction always negative? Is the work done by gravity always negative? Spring as well? It seems ...
360 views

### Correct definition of an 'acoustic mode'?

I am reading 'The Oxford Solid State Basics' by S.H.Simon in which on page 92 defines an acoustic mode as: ... any mode that has linear dispersion as $k\rightarrow 0$. Whilst on page 94 he defines ...
307 views

### Is the Lorentz force a vector field or just a vector?

I've heard both yes and no. Is the Lorentz force a vector field or just a vector? $$\mathbf{F}=q(\mathbf{E}+\mathbf{v}\times \mathbf{B})$$
138 views

### Can magnitude be negative?

My teacher told that magnitude is the positive value of that quantity or the modulus of that quantity. he also told that vector quantities have both magnitude and direction and scalar quantities have ...
61 views

### Definition of Vector

In a book on General Relativity that I am reading, it defines a vector as an object or array of numbers that transforms like a vector (under rotations). I understand that under rotation $\theta$, a ...
241 views

### Definition of one-particle irreducible diagrams

Text books often defines one-Particle Irreducible diagram (1PI diagram) as a connected diagram which does not fall into two pieces if you cut one internal line. Is this internal line the full ...
1k views

### Are events in this experiment simultaneous if observed in platform's frame?

In some contexts e.g. on Wikipedia it is defined as a matter of happening . In others(e.g. as defined by Einstein in his book "Relativity the special and general theory") it is defined as a matter of ...
65 views

### What is the definition of time? [duplicate]

I wanted to know the definition of time just like as we define displacement, current etc. **Note:**There should be no mention of time period or time interval in the definition.
8k views

### What is the difference between a bounded orbit and a closed orbit?

Goldstein's Classical Mechanics has a puzzling few sentences in his discussion of orbits. Referring to the case of orbit where the energy is low enough for the orbit to be bounded, he says :"This ...
287 views

### Physical Interpretation of the Diffusion Constant $k$

I have read technical explanations of the interpretation: ''Diffusion coefficient is the proportionality factor D in Fick's law (see Diffusion) by which the mass of a substance dM diffusing in ...
105 views

### Definition of temperature ambiguity

Temperature is defined as $$\frac{1}{T} \equiv \left(\frac{\partial S}{\partial U}\right)_{N,V}.$$ However, a system with a fixed temperature does not have a fixed amount ...
2k views

### Clarification regarding Newton's Third Law of Motion and why movement is possible [duplicate]

Newton's third law states that to every action, there is an equal and opposite reaction. If that's the case, then how do things move at all? Shouldn't all applied forces be canceled by the equal and ...
313 views

### Reality constraint

What is the "definition" of a reality constraint and why is it called that way? (I mean how it is used for example in quantum field theory and string theory.)
1k views

I report some definitions of flow characteristics as given on Cengel Cimbala. Laminar or turbulent Laminar flow: A stable well-ordered state of fluid flow in which all pairs of adjacent fluid ...
602 views

### Scientific definitions of “moment (of)” and “instant”? [closed]

What are the scientific definitions of "moment (of time)" and "instant"? Are they different with their definitions in everyday language? I also don't know the definitions in everyday language, of ...
463 views

### In the formula for work, $W=\vec{F}\cdot \vec{d}$, is $\vec{F}$ the resultant force?

Is the force $F$ the resultant force on the object, or exactly the force needed to move the object? e.g.: I might 'need' only 1 N to move an object over 1 metre, but if I apply a 10 N force to that ...
130 views

### What's the difference between “spectromicroscopy” and “microspectroscopy”? [duplicate]

Both definitions that I found are rather vague. (Related question: What's the difference between microscopy and spectroscopy?)
160 views

### Is $\delta Q – \delta W$ a state function?

I know that internal energy, $Q+W$ is a state function. But $$dU=\delta Q-\delta W,$$ is the change in internal energy, where $dU$ is change in internal energy, $\delta Q$ is the heat supplied to the ...
2k views

### How do we define what is “External” force or “Internal” force in the context of momentum conservation?

I know that without presence of any "External" force momentum is always conserved. But how do we distinguish between "External" force and "Internal" force where all are "Force"?
37 views

### Confusion regarding EMF definition

The emf of the battery source can be defined as the potential difference between two electrodes when no current is flowing. Now how I can apply this definition of the emf which is produces by change ...
481 views

### What does a Galilean transformation actually mean?

What does a Galilean transformation actually mean? I'm having trouble defining the equation for displacement shifts $x'=x-vt$. Does it mean that to any event $C$ the displacement in the primed ...
77 views

### How do I understand Kinetic energy formula? [duplicate]

$$\frac{mv^2}{2}= Kinetic Energy$$ Can you explain me? What is purpose of $v^2$, $mv^2$, I am trying to understand the formula.
5k views

### What is the definition of an exchange particle?

After reading through articles, i concluded that a suitable definition is that when 2 particles interact bosons are exchanged between the 2 particles creating a force? What would a good definition be ...
367 views

### Is this circuit a series or parallel circuit?

I saw a definition of a parallel circuit as a circuit with more than one path for current to flow. Is that the definition that's accepted? It seems like a good definition to me, but does that mean ...
2k views

### What is a conservative force?

Currently I have three different pictures to describe/understand conservative forces. For the moment I just want to get an electron from point A to point B. In the near surrounding is another electron ...
160 views

### Why is the moment of inertia the integral of the “second moment”? What is the derivation for the formula? [duplicate]

In my dynamics textbook, the introduction to the moment of inertia reads: "Moment of inertia is the integral of the "second moment" about an axis of all the elements of mass dm which compose the ...
315 views

### Meaning of potential with respect to Earth

Potential of a body is defined as the amount of work done in bringing that body from infinity up to some point divided by its charge. The Earth has zero net charge, so the work done in bringing any ...
4k views

### Definition of Free Electrons and Mobile Charges?

Could someone please give me a good definition of the following electric terms? Despite what searching I have done, I have not come across a definition that I have found clear for me to understand: ...