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Questions tagged [models]

DO NOT USE THIS TAG just because the involved physics is based on a model. All physics descriptions are inherently model-based. This tag is reserved specifically for addressing model development, validity, simplification, or other meta-model questions.

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How can i calculate the upwards force applied by a water jet on a suspended sphere

First of all, i would like to possibly clear a few things up: yes, i do know the weight of the ball, but i would like to be able to calculate the upwards force of the water jet on the ball. (hence, i ...
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0answers
78 views

Is the field of quantum mechanics just guessing math formulas to fit data? [closed]

I don't understand quantum mechanics, and I am basically wondering how research is done in this area. I don't intuitively see what's going on, and from what I've been hearing, nobody understands it ...
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1answer
106 views

Time evolution of molecular signal from a laser-induced plasma - finding the right model for my data

I am looking at molecular emissions in laser-induced plasma plumes created in argon at reduced pressure (in the mbar range). To be precise, these are heteronuclear diatomic molecules that emit ...
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2answers
97 views

Can we create new physics through moderately brute force computing? [closed]

So my argument for this is that the expansion of knowledge in any field of physics depends on what is previously known, and what we physicists express or knowledge as equations. So here's what I ...
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1answer
39 views

Modeling heat transfer of a long pipeline with heated fluid and flow as a lumped system with time delay

I want to model the heat transfer of a very long pipeline and how heated fluid is flowing through this system. It is possible to model this system as a distributed system. However I want to model this ...
2
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1answer
157 views

How to test quantum mechanics?

In this paper, Testing quantum mechanics, S. Weinberg states that The problem is to know what to test. Usually we can get guidance on how to test a theory like general relativity or the standard ...
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0answers
9 views

What are the assumptions for porous media to be considered as continuum?

The poroelastic models like - Biot theory- are built on the continuum approach. But I am not able to understand, how this heterogeneous media can be considered as a continuum. However, If the porous ...
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6answers
4k views

Why exactly are singularities avoided or “deleted” in physics?

What is the real reason that make us reject singularities everytime we see them in a theory/model? For example, in GR, it is predicted that black holes singularities have infinite density. This makes ...
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0answers
20 views

Is this a simple fracture mechanics model

If I use the interatomic potential $V(x_i-x_j)= \frac{1}{2}k(x_i-x_j-a)^2$ for $|x_i-x_j-a|<b$ $V(x_i-x_j) = V_0$ for $|x_i-x_j-a|\geq b$ for the critical displacement $b$ and Equilibrium ...
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3answers
38 views

Finding the equations of motion with observations

Let's say that we don't know the equations of motion. I will try to predict where my ball will fall when I shoot it with an angle $\alpha$ and and speed $v$ by finding the function that describe this....
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0answers
16 views

Aggregation phenomena : How to get from a discrete to a continuous point of view

I'm studying a diffusion limited aggregation phenomenon. The $N$ particles diffuse in a box and when there is a contact they stick with a probability $p$, and let's say to simplify $p=1$. Meaning that ...
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0answers
34 views

High-energy effective field theory

Usually when one speaks of effective field theories, one is looking to integrate out certain fields which are typically heavy in comparison to the regime of interest. That is one has a theory at a ...
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1answer
33 views

Application of linear constant coefficients ODE of the second order [closed]

I've asked this question in math forum. Apparently this question is not welcomed there. So maybe here I can get a proper response. Consider ODE in the form of $$y''+ay'+by=f(t)$$ where $a$ and $b$ are ...
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1answer
70 views

Laplace transform on thermodynamics equation

I'm trying to create a simple model of a single-flash geothermal plant which consist of 3 main parts (flash-separator, turbine, and condenser). Is there any way to create a transfer function using ...
3
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1answer
47 views

Theories, Corollaries, and Models

I apologize if this question seems overly basic. I was wondering how to recognize what a theory is really saying, as opposed to the explanation/corollaries that are drawn from it. As an example, take ...
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1answer
39 views

Numerically Modeling Coupled Oscillators Point Masses

I seek to model the motion of two coupled oscillating point masses as shown below: Note that x1(t) models the leftmost point mass and x2(t) is the motion of the rightmost point mass. I would like to ...
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2answers
83 views

Do we know, or at least have a strong argument for the fact that for a given time interval, we can always find a smaller time interval? [duplicate]

Motivation: In Biology, when, for example, biologists try to model the population dynamics of a population, they say: Let $N: \mathbb{R}^{nn} \to \mathbb{R}^{nn}$ be a function that represents ...
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0answers
26 views

Resource to learn modelisation of quantum measurement

I need to learn how we do model quantum measurement (for experiments for example). If we study a quantum system X, when we measure it we usually consider a projective measurement (so we use the ...
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1answer
36 views

How do we generalise a specialised case in physics?

I have come across this sort of thing a lot of times in my textbook. I give the examples below- Eg.1- In the case of a capacitor connected across an alternating current generator, we find $V_c=...
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1answer
79 views

If two different theories describe experimental observations equally well, can one be said to be more valid than the other? [closed]

Assuming both use accepted rules of logic, which of the two theories would be accepted and on what basis, for example: simplicity etc.
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1answer
71 views

Models in physics [closed]

As I said in another question I am just a physics enthusiast so I am sorry for my very poor knowledge. What is meant by models in physics? what is their function and why physicists imply them? Are ...
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9answers
4k views

How does a particle know how to behave? [duplicate]

How does a particle know it should behave in such and such manner? As a person, I can set mass is so and so, charge is so and so - then set up equation to solve its equation of motion but who ...
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1answer
46 views

Uncertainties in measurements and slopes

Suppose I have a mathematical model $y=mx$ and I have data for $x$ and $y$ and I want to fit the mathematical model on the data and determine the value of slope. I also have uncertainties of $x$ and $...
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2answers
91 views

Physical meaning of quantized energy of electron (or n=1,2,3…) in Bohr's model

To solve objections on Rutherford's model, one of which is energy deficit, Bohr postulated that the energy of the electron is quantized and $n=1,2,3...$ . But what does this postulate mean physically? ...
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14answers
2k views

How can the solutions to equations of motion be unique if it seems the same state can be arrived at through different histories?

Let's assume we have a container, a jar, a can or whatever, which has a hole at its end. If there were water inside, via a differential equation we could calculate the time by which the container is ...
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4answers
66 views

Mechanical Energy Analog to Capacitance

For starters I am a complete physics noob. I've been trying to understand basic fundamental ideas at a conceptual level I was drawn to the fact that work $(J) = FxD = CxV.$ I started trying to find ...
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1answer
50 views

From Bose-Hubbard model to quantum rotor model

For the Bose-Hubbard model: $$H=-t\sum_{\langle i,j \rangle}(b_i^{\dagger}b_j+b_j^{\dagger}b_i)+K\sum_{i}(\hat{n}-n_0)^2$$ In the large-filling limit, we can replace $\hat{n}$ by $\hat{n}+n_0$, and ...
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3answers
57 views

Regarding assumptions

In most of the theories or derivations we take some assumptions like has is ideal, frictionless piston and many more but these are not applicable in real world. But in our real life situations we ...
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0answers
60 views

Has anyone ever actually considered a spherical cow? [closed]

Yes, I'm aware this question is somewhat whimsical. I'm sure every physicist is familiar with "Consider a Spherical cow". Has a cow (or any animal for that matter) ever been assumed spherical for ...
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1answer
65 views

Vacuum Conditions in teaching high school physics

I'd like to know why in high school physics is taught mostly in vacuum conditions instead of terrestrial ones. I don't mean one is more important than the other, but it's just a curiosity about that.
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1answer
42 views

Modelling how a macroscopic detector interacts with a quantum mechanical particle?

Background I recently came up with a math formula and wondered if could be useful for any physical kind of situation. I then, realised it might be useful for the situation of particle detector. P.S: ...
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1answer
54 views

Any physical basis for this pressure vs flow model across flow restriction?

Recently read a journal paper on biomedical engineering where the authors used the following expression to model the expected volumetric gas flow, $Q$ from a pressure potential $\Delta P$ : $$\Delta ...
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2answers
38 views

Distinction between “assumption”, and “build in definitions” - What is considered an assumption in a physical model?

This question I want to deal with the basics of modelling a physical theory: Let's say we start with observing in the world (be it little bubbles in the water, a particle moving, a pattern in the ...
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1answer
82 views

How to teach modeling physical systems?

While working as a teaching assistant for introductory experimental physics classes (newtonian mechanics and electromagnetism) for the last couple of years, I faced a certain kind of issue again and ...
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4answers
189 views

How are theories selected?

My motivations for asking this question are philosophical but I think this is a question that is best answered by the physics community. There is a problem in the philosophy of science called the '...
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3answers
79 views

What are point objects?

I can't seem to get the idea of point mass into my head. Why are equations of physics applicable on only point masses and should be altered while dealing with object that has a collection of points? ...
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0answers
101 views

Wigner 's unreasonable effectiveness of mathematics in natural sciences [closed]

This question is related to Wigner's problem, related to the unreasonable effectiveness of mathematics in natural sciences. Understanding a phenomenon means constructing a mathematical model , and ...
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1answer
93 views

Are physics advancements pure mathematical realizations? [closed]

Hello Physics Stack Exchange! I'm from Mathematics Stack Exchange and recently watched a TedTalk on the fabric of nature being mathematics itself. The more I pondered this, I wondered about the ...
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0answers
63 views

Can I use calculus to calculate how fast a the cracker of a whip is moving when it cracks?

So I know that when a whip cracks it is breaking the sound barrier and makes a sonic boom. I understand that this is Because of conservation of momentum as the whip tapers in thickness and hairpins at ...
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2answers
165 views

Why in physics does one ask increasingly fundamental questions of matter? [closed]

Many physicists seek to understand grand theories of everything by reduction to smaller components or building blocks. Those trained, but maybe are not practicing talk about the importance of "first ...
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1answer
35 views

Equation of motion of ducks from a data set

I am reading this paper that models the equation of motion of a group of ducks (surf scoters) as observed in Vancouver. The full paper and supplementary information can be downloaded here: http://...
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3answers
806 views

Where does the use of tensors to describe orientation dependence of physical phenomena arise from?

In the context of anisotropy, I have often read that the use of a rank 2 tensor is "a model". But what is the idea behind this choice? Can anyone describe in what sense the use of tensor in this ...
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1answer
182 views

Is there a physical model described by this equation? (vectorial damped wave equation)

Consider the wave equation $\partial_t^2 u\left(t,x\right) - \Delta u\left(t,x\right) = 0$ where $t\in\mathbb{R}$ is the time variable and $x\in\Omega$ (a nice open subset of $\mathbb{R}^n$) is the ...
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0answers
127 views

Hubbard Model: Mean field theory and ferromagnetism

For the single-band Hubbard Model, I want to write down a mean field theory for the possibility of occurrence of ferromagnetism in the ground state. For the model given by $$\hat{H} = -t \sum_{\...
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2answers
198 views

Is velocity of the electron quantized in Bohr's model?

I know that angular momentum and energy of the electron is quantized in the model. When we wrote down the equations and get the velocity equation, if I am not mistaken, we find the velocity to be ...
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1answer
52 views

Finding the cost functional of a car-following model [closed]

I have a car-following model with delay $\ddot{x}_n(t)=\lambda [\dot{x}_{n-1}(t-T)-\dot{x}_{n}(t-T)]$, where $\ddot{x}$ is the acceletation, $\dot{x}_{n-1}-\dot{x}_{n}$ is the relative velocity, $\...
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1answer
22 views

Multi-stability potential is suitable for interdisciplinary branches of science?

The potential function $V(x) = c(x-a)^2(x-b)^2$ with constants $a,b,c$ and some variable $x$ has two minima: One at $x=a$ and another at $x=b$. When plugging this potential function in Newton's ...
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2answers
146 views

Do we study the true nature of the universe or reality or just create a model (mathematical) to get approximation close enough to our use? [closed]

Do we study the true nature of the universe or reality or just create a model(mathematical) to get approximation close enough to our use? whether they have to do any thing with reality or not. I have ...
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2answers
472 views

Magnetic field due to current carrying wire at the wire [closed]

What is the magnetic field due to current carrying wire at a point on the wire itself?
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1answer
141 views

Maths and physics agreement [closed]

This might be a semi-philosophical question - sometimes when we solve a physics problem, the maths gives solutions that are tossed out as "non-physical", and we keep only the solutions that make ...