What is Particles: Definition and 1000 Discussions

In the physical sciences, a particle (or corpuscule in older texts) is a small localized object to which can be ascribed several physical or chemical properties such as volume, density or mass. They vary greatly in size or quantity, from subatomic particles like the electron, to microscopic particles like atoms and molecules, to macroscopic particles like powders and other granular materials. Particles can also be used to create scientific models of even larger objects depending on their density, such as humans moving in a crowd or celestial bodies in motion.
The term 'particle' is rather general in meaning, and is refined as needed by various scientific fields. Anything that is composed of particles may be referred to as being particulate. However, the noun 'particulate' is most frequently used to refer to pollutants in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.

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  1. G

    I How to envision particles in superposition in Many Worlds presplitting

    Should particles in superposition before quantum decoherence (many worlds) be envisioned in the same exact way as they are envisioned before wave function collapse (Copenhagen)? Clearly, the particle in Many Worlds is in a sort of superposition, but with all of the talk about one universal wave...
  2. M

    Fermions, Bosons, and nonidentical particles in a 1-d oscillator

    I'm having a hard time understanding how to treat fermions, bosons, and distinguishable particles differently for this problem. To the best of my understanding, I know that my overall state for bosons must be symmetric, and because they're spin-0, this means there's only one coupled spin state...
  3. F

    Motion of particles close to the Earth

    I tried to solve the problem in 2 ways, first using lagrangian mechanics and second by putting a rotating reference frame on the initial take-off point. However I cannot be sure if the equations of motion for the two solutions came out the same. A-) Equations of motion from Lagrangian...
  4. H

    I Information diagram for entangled particles?

    Hi Pf I read that when two particles are maximally entangled , all the information is in the correlations between the particles. If we need 1 bit to describe one particles. Are two bits in the correlations? three particles may be entangled and then we need to considere 3 bits. As entanglement...
  5. T

    Connected Particles Question (ENGAA 2019)

    The correct answer is 'C'. Why is my working wrong?
  6. thaiqi

    Deriving Statistical Behavior of Particles via Classical Mechanics

    Hello, using computation simulation, can the statistical behavior of many particles be derived through deterministic classical mechanics?
  7. Kosdon3200

    I What are these directional energetic particles?

    In addition to the usual alpha and beta particles visible in my condensation cloud chamber, I see occasional tracks that seem highly energetic -they easily penetrate the entire width of the cloud chamber (10-12 inches) going in one side and out the other. More mysteriously, their orientation is...
  8. H

    A Exploring Fringe Visibility from Entropy of Two-Level Particles

    i consider a pair of two level particles which can be up or down. this pair is described in the tensor product by the unitary vector (cos(\theta) (du + ud) + sin(\theta) (dd + u)) /\sqrt 2 i take its density matrix , trace it on one of the two particles and find the density matrix of each one...
  9. greg_rack

    Kinetic energy transformed in a collision involving coalescing particles

    This problem got me kinda confused since I cannot really understand the question... who tells me how the energy dissipated in this case? Has it all transformed into heat to cause the coalesce of the two particles, or ar the two particles now merged together still traveling with a certain amount...
  10. S

    Electrostatics problem with charged particles accelerating

  11. LuisBabboni

    I Virtual particles and Heisenberg

    Hi people. Having as uncertainty principle that ΔE Δt≥ h/4Pi, why Δt≤ h/4PiΔE to allow the existence of a virtual particle? How ≥ becomes ≤ ? I think... real particles must obey ≥ so any particle that do not obey that is a virtual particle and thus why virtual particle needs to obey Δt≤...
  12. Boltzman Oscillation

    I Particle Perspective: How Relativity Affects Us

    Some background, I am an undergraduate electrical engineering student with a knack for physics. I plan to attend graduate school for physics but for the meanwhile I've only taken an undergraduate course in QM mechanics, which used griffith's book, and a modern physics course, which covered some...
  13. P

    B Actions of subatomic particles while under observation

    Hi my name is tim. I have a new found like of the inner workings of or universe , and am currently considering which field i should go into. As of now I am considering computer science. But to me, in my opinion, we as in humans created computers, therefore the science is technically already in...
  14. E

    Net electric force of multiple charged particles in 3-d space

    I draw the graph like this: For (b), I divided each force vector to e from p1 and p2 as x and y parts. I computed them and got Fx=-4.608*10^(-15)N Fy=-2.52*10^(-15)N However, I am not sure whether I did it correctly or not... I appreciate every help from all of you! Thank you!
  15. nomadreid

    I Does intrinsic (e.g., spin) imply elementary (irreducible)?

    Some time ago, before particles turned out to be mutable wave excitations (making Alchemist's dreams sound nicer, I guess :-) ) , to say that something was an "elementary particle" meant that it couldn't be broken down further. OK, that idea bit the dust, but now there are intrinsic...
  16. B

    I How do you get polarized charged particles?

    Hello! how does one produced big ensembles of polarized charged particles (electrons, protons, muons etc.) for certain experiments? In the case of neutral particles (for example the nucleus in an atom) this could be done using a magnetic field, but I guess this won't work that straightforward...
  17. R

    I Measuring Entangled Particles in two different Basis

    Consider two entangled spin half particles given by the generic form of Bell Equation in Z-axis: ##\psi = (a\uparrow \uparrow + b\downarrow \downarrow)## where ##a^2+b^2=1## In a (2D) planer rotated (by an angle ##\theta##) direction the new equation can be given by: ##|\psi \rangle =...
  18. R

    I Measurement of an entangled Particles in two Different Bases

    Consider two entangled spin half particles given by the generic form of Bell Equation in Z-axis: ##\psi = (a\uparrow \uparrow + b\downarrow \downarrow)## where ##a^2+b^2=1## In a (2D) planer rotated (by an angle ##\theta##) direction the new equation can be given by: ##|\psi \rangle =...
  19. docnet

    B How does the LHC send same charged particles against each other?

    How does LHC send same-charged particles in opposite directions?
  20. AidenPearce

    B When are particles in a superposition of states?

    Hi guys, I hope you all are doing great. If we take the double slit experiment for instance, before measurement particles are in a superposition of states. Once they are "measured", or non arbitrarily interfered with, their wave function collapses and only one state remains. So my question is...
  21. CarawayBlossom

    I Measurement of Entangled Particles causes up or down spin?

    In reading around, it seems that in the case of entangled particles, it is the measurement of one of the particles that causes the other one to be it's opposite spin and that there's some means of info transfer going on caused by the measurement. I'm not understanding why it would not be that...
  22. J

    A Griffith's Elementary Particles Section 9.7 Electroweak Unification

    1. On pg. 343 Griffith's expresses the weak current in terms of left-handed doublets. jμ± = ##\bar χ_L##γμτ±##χ_L## ##χ_L## = ##\begin{pmatrix} ν_e \\ e \end{pmatrix}_L## ##\tau^+## = ##\begin{pmatrix} 0 & 1 \\ 0 & 0 \end{pmatrix}## , ## \tau^- ## = ##\begin{pmatrix} 0 & 0 \\ 1 & 0...
  23. S

    A How does the number of particles increase the surface adsorption?

    How the number of the particles in a solution increase the probability to get adsorption on a surface? which physical terms explain this? For example when I increase the concentration of molecules in a solution I can see that the adsorption and the aggregation on the surface happen.
  24. S

    A Diffussion-limited aggregation and the mobility of particles

    How a high mobility of particles over surface cause to aggregation, the professor in the class said that "high mobility causes to local equilibration and thus to a compact aggregation".. which I didn't understand..! What does he mean about local equilibration and how all connect to each other?!
  25. Helena Wells

    A If Neutrinos are majorana particles, does this mean lepton number is not conserved?

    If neutrinos are majorana particles does this mean that lepton number is not conserved in particle reactions? And I only noticed neutrinos are only produced when the decay of a particle to some other particles is carried by the W bosons ( weak interaction ). Is it possible the weak interaction...
  26. tanaygupta2000

    Finding the Line of Motion of Two Particles

    I know that I need to find the equation of the line of motion of the two particles, the dot product of which with one of the options will give 0. I began with founding the coordinates of center of mass: R = (m1r1+m2r2)/(m1+m2) = (2a/3, 0, a/3) and velocity of the center of mass: V =...
  27. SchroedingersLion

    A Lennard Jones, 3 particles, partition function

    Greetings, similar to my previous thread (https://www.physicsforums.com/threads/lennard-jones-potential-and-the-average-distance-between-two-particles.990055/#post-6355442), I am trying to calculate the average inter-particle distance of particles that interact via Lennard Jones potentials...
  28. A

    Particles on Deforming Surfaces: Theory & Analysis

    All books in analytical mechanics explain the case of a particle moving on a given static surface. But what happen if, for example, the surface is having some deformation?. I imagine that the principle of virtual work, and hence, D'Alembert are no longer valid since the normal force by the...
  29. Souma

    I The "size" of entangled particles

    Hello everyone, I hope you are having a nice day, I was reading [The principles of Quantum Mechanics by P.A.M Dirac], and I was attracted to the definition of size. The book says: "If the object under observation is such that the unavoidable limiting disturbance is negligible, then the object...
  30. LCSphysicist

    Distance between two particles

    So we have 5 incognits 5 equations, is not hard, but need attention. What you think about? Right? This type of question is generally more easy to solve, do you know any trick?
  31. Sabertooth

    A Relativistic Effects on Particles and Gases

    Hello everyone, I was doing some calculations recently regarding particle velocities for different elements at different temperatures and I have a few questions for the experts in here. Usual gas laws in my school book provides information about the velocity of particles in gases, it provides...
  32. S

    Center of mass energy for two relativistic colliding particles

    Starting from the center of mass energy S = (E_{1} + E_{2})^2 - (\vec{p_1}+\vec{p_2}) knowing that E^2 = m_{0}c^4 + p^2*c^2 one has S = (E_{1} + E_{2})^2 - (\vec{p_1}+\vec{p_2}) = ( m_{0}c^4 + p_{1}^2*c^2) + m_{0}c^4 + p_{2}^2*c^2)^2 - p_{1}^2 - p_{2}^2 - 2p_{1}p_{2}cos \{theta} and then...
  33. SchroedingersLion

    Lennard Jones Potential and the Average Distance Between Two Particles

    Greetings! Suppose I have 2 particles that interact via a Lennard Jones potential $$U(\mathbf{q}_{1}, \mathbf{q}_{2}) = 4 \epsilon \left[ \left( \frac{\sigma}{r} \right)^{12} - \left( \frac{\sigma}{r} \right)^6 \right] $$ with interparticle distance ##r=|\mathbf{q}_{1} - \mathbf{q}_{2}|##. The...
  34. LCSphysicist

    Block bombarded by particles {colision}

    I thought i could apply a conservation of momentum in this case, Apparently, this is not right, so i don't know what to do now.
  35. SamRoss

    I Seeking better explanation of some quantum stats formulae

    In "Introduction to Quantum Mechanics", Griffiths derives the following formulae for counting the number of configurations for N particles. Distinguishable particles... $$ N!\prod_{n=1}^\infty \frac {d^{N_n}_n} {N_n !} $$ Fermions... $$ \prod_{n=1}^\infty \frac {d_n!} {N_n!(d_n-N_n)!}$$...
  36. sophiatev

    I What happened to the spatial degrees of freedom for the second particle?

    In Henley and Garcia's Subatomic Physics, they introduce phase space in chapter 10 by considering all the possible locations a particle can occupy in a plot of ##p_x \ vs. x##, ##p_x## being the momentum of the particle in the x direction. They next consider an area pL on this plot, and state...
  37. HexHammer

    B Virtual Particles are not Dark Matter?

    So far as I understand it, a photon can split up and create particles with matter, even though the photon is massless, yes? So if a photon can be more places at the same time, it should be able to create multiple particles all at once? So how is this not Dark Matter?
  38. J

    B String Theory & Elementary Particles: What's Real?

    If string theory is correct does it mean that elementary particles like photons, electrons, and quarks don't really exist or does it mean they do but are made of cosmic strings and so therefore are not elementary?
  39. B

    A Could the fields for the particles and forces have the same origin?

    I was watching this terrific lecture by David Tong and there was a section at the end from around 50:12 - 54:00 that I found particularly fascinating. I am very much a layman when it comes to these topics and my question may be silly, but what sort of ideas are there that state that all the...
  40. angela6884

    B Relationship between wavelength and concentration of particles

    What is the relationship between the wavelength produced by a laser and the concentration of particles in the air? Does the wavelength get larger if the concentration of particles the beam hits increase?
  41. E

    A single external force doing work on a system of particles

    Suppose we have a system of particles being acted upon by a single external force ##\mathbf{F}^{e}##. Each individual particle feels a force of ##\mathbf{f}_i = \mathbf{f}_{i}^{int} + \mathbf{f}_{i}^{e}## such that ##\sum_i \mathbf{f}_{i}^{e} = \mathbf{F}^{e}##, and ##\mathbf{f}_{i}^{int}## are...
  42. B

    Dimension of Hilbert spaces for identical particles

    My thoughts are: a) it should just be N^2 b) just N since they're identical c) due to Pauli exclusion would it be N^2 - N since they have to be different states?
  43. E

    Mixing of two polymer particles heated above Tg

    I am wondering if two polymer particles, of same kind, heated above Tg can be mixed, over time, if they are squeezed together. By mixing I mean that the surfaces of the two particles will mix into one after they are squeezed together. For simplicity let's assume that the polymer particles are...
  44. PeroK

    Insights A Beginner Physics Guide to Baryon Particles

    Continue reading...
  45. J

    I Group Theory Appearing in Griffith's Elementary Particles (2nd Ed.)

    Hello, I'm trying to make sense of some of the group theoretic discussion found in Griffith's Introduction to Elementary Particles. I have had a fair amount of exposure to elementary group theory, but no representation theory, and have some specific questions related to this which refer to the...
  46. A

    B Fundamental particles and mass quantization

    We know that the energy levels for electrons surrounding nucleus are quantized , only coming in discrete levels. When I see the standard model of elementary particles table I notice specific masses for each of the particles whether they be quarks or leptons or bosons like the higgs. I know that...
  47. C

    Relative motion of 3 particles

    Velocity of B wrt C = (v +v*cos 60) i^ - vsin60 j^ = (3v/2)i^-((3)^(1/2)/2v)j^ But since C is also moving this initial velocity would vary. So how to find a function which defines its path and hence I can find time at which the particles meet. I was told to take rotating frame of reference that...
  48. A

    I Frank Wilczek on Virtual Particles and Summing diagrams....

    Hi all, - an initial apology - there are a large number of threads on virtual particles on the site, and I apologize for adding another one. I had two questions - on a related note, the guidance provided by @A. Neumaier's FAW on virtual particles has been highly valuable for a novice . 1) Upon...
  49. B

    A rotating system of two point particles with inner torque

    Lets say we have a system of two point particles (1. and 2.) which are rotating around an axis. What is written next in my physics course book is: The torque of a 2.body on the 1. body is M21=r1xF21 and the torque of the 1.body on the 2.body is M12=r2xF12. Understandable. But how? There is no...
  50. Z

    Spatial Wave function of two indistinguishable particles

    Hi, I just need someone to check over my work. I am having trouble with the next part of this question and I just wanted to check that this part was correct first. I have two particles in an infinite square well (walls at x=0 and x=L). I need write an expression for the spatial wave...
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