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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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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
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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
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Is there any evidence that 'anthropogenic climate change' greenhouse radiative models describe real atmospheric processes?

The radiative models used by the IPCC predict in case of a doubling of the preindustrial CO2 concentration of 285 ppm in the atmosphere - the current value is 405 ppm - an increase in backradiation or ...
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33 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
31 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
42 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 ...
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1answer
45 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
33 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
82 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
23 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
71 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
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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
40 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
85 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
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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
60 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
45 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
55 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
58 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
64 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
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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
52 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
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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
78 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
185 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
77 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
90 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
90 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
60 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
137 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
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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
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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
179 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
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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
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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
51 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
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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
139 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
353 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
140 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 ...
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1answer
32 views

A good model for velocity(t) such that it asymptotically approaches a max value

In many cases a powered vehicle accelerates its fastest at lower speeds. Then as the speed increases, the acceleration approaches zero and the max velocity is approached. What differential equation ...
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1answer
30 views

What are all the possible ways to achieve acoustic resonance in a cavity?

If one were to observe acoustic resonance in a cavity (semi-closed volume of space) what is the complete list of potential hypotheses as to the cause? In my limited experience I can list the ...
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1answer
92 views

The Helmholtz resonator, what's actually resonating?

I'm trying to more closely understand the physical mechanism behind the Helmholtz resonator. If I model the resonator in terms of an analogous series linear electrical circuit: resistance ($R$), ...
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2answers
480 views

Liquid density as a function of pressure and temperature, how to model experimental data of $\rho(p,T)$?

I’m going to ask my question, explain the problem, show what I have done, and then re-state my question. (Note, perhaps this is a question better suited for https://stats.stackexchange.com/ or https:...
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1answer
109 views

About the consequences of $\mathbb{Z}_2$ invariance in dark matter models

This well-cited paper talks about is a minimal renormalizable extension to the Standard Model (SM) to incorporate particle dark matter (DM) into it by adding a real scalar field $S$ which (unlike the ...
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1answer
176 views

Calculate the enthalpy of a pure compound with a cubic equation of state

I would like to calculate the enthalpy of a pure compound with a cubic equation of state (the ones deriving from the Van der Waals equation of state). I have an analytic expression of the heat ...
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1answer
43 views

Self-organizing pattern of magnetic domains

I would like to model an structure like this: using simple methods like cellular automata or networks. The picture is signed as "a self-organizing pattern of magnetic domains in cobalt". I'm not a ...
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2answers
430 views

If ball bouncing looks like a modulated absolute value of a sine wave, then why not model bouncing this way?

If ball bouncing looks like a modulated abs of sine wave, then why not model bouncing this way? Rather than this way: https://se.mathworks.com/help/simulink/examples/simulation-of-a-bouncing-ball....