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. 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...
  2. 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...
  3. 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...
  4. 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...
  5. tanaygupta2000

    Understanding Energy of Particles with 'x' Degrees of Freedom

    I've learned that for a particle having 3 degrees of freedom, its average energy is 3/2 kT. So for a particle having 'x' degrees of freedom, its energy should be xkT/2. So what is the use of given E = ax6 here? Please help!
  6. tanaygupta2000

    Statistical Mechanics: Four non-interacting particles are confined in a box

    Regarding the first part, I proceeded as: nx ny nz 4 0 0 => E1 = 16C 0 4 0 => E2 = 16C 0 0 4 => E3 = 16C 3 1 0 => E4 = 10C 3 0 1 => E5 = 10C 0 3 1 => E6 = 10C 1 3 0 => E7 = 10C 0 1 3 => E8 = 10C 1...
  7. Elbow_Patches

    B Absorption of beta particles by lead

    Hello everyone, We conducted an experiment with a strontium-90 source and some different thicknesses of lead. With 2.1mm of lead the count rate (corrected for the background) was 0.69 counts per second, 3.0mm 19.7cps 6.8mm 15.4cps 13.8mm 10.0 cps This would...
  8. F

    B Where do virtual particles come from?

    I watched a Youtube! video on black holes, and it said that black holes evaporate via Hawking radiation. If I understood the video correctly a virtual particle can pop into existence just outside the event horizon, and that one of the resulting pair can subsequently fall back into the black hole...
  9. C

    B States of Matter - particles or atoms?

    Resources I have looked at distinguish between the three basic states of matter in terms of how closely particles are held together; i.e. in solids they are bound most closely, in liquids less so and in gases they're much freer. Would it not be more correct to refer to how closely atoms or...
  10. Ranku

    I Energy of massless particles before electroweak symmetry breaking

    Would it be correct to represent the energy of massless particles before electroweak symmetry breaking as ##E = cp##, just as we do with photons post-symmetry breaking?
  11. Frigus

    Forces between subatomic particles in a molecule

    I was seeing a video about molecular orbital theory..at t=3:56 he counted the forces but I don't why he didn't considered repulsions between electrons. Please can you tell me why he didn't considered repulsions?
  12. A

    I On-shell virtual particles and 'physical' Hilbert spaces....

    Hi all, Just a clarification question as I'm learning. It's possible to have Feynman diagrams where the internal lines (virtual particles) are in fact on shell. 'On shell' would imply 'observable,' (maybe?) but as noted in @A. Neumaier's great FAQ, only sets of Feynman diagrams have predictive...
  13. Hemanta

    Comparing the KE of Alpha and Beta particles

    I try solving it but the answer didn’t match
  14. W

    I Inner Product Between States of Multiple Particles

    $$<p_1 p_2|p_A p_B> = \sqrt{2E_1 2E_2 2E_A 2E_B}<0|a_1 a_2 a_{A}^{\dagger} a_{B}^{\dagger} |0>$$ $$=2E_A2E_B(2\pi)^6(\delta^{(3)}(p_A-p_1)\delta{(3)}(p_B-p_2) + \delta^{(3)}(p_A-p_2)\delta^{(3)}(p_B-p_1))$$ The identity above seemed easy, until I tried to prove it. I figured I could work this...
  15. P

    Particle decaying into two daughter particles - special relativity

    Right, so I thought I'd done this correctly but clearly not because my velocity is greater than the speed of light, where have I gone wrong? P = (M, 0, 0, 0) p1 = (E1, p1x, p1y, p1z) p2 = (E2, p2x, p2y, p2z) P = p1 + p2 p2 = P - p1 square each side to get (p2)2 = P2 - 2Pp1 + p12 therefore (m2)2...
  16. A

    I Does p=mc Apply To Photons? | A.P. French's Special Relativity

    In A.P. French's Special Relativity, the author said the following, As I understand, photons are massless, so I don't think the last equation above applies to photons, but then, when deriving it, he used an equation proper to photons (##E=pc##). So in which context is ##m=p/c## valid?
  17. Quantum Alchemy

    I Questions about QFT and the reality of subatomic particles

    I've been reading about Quantum Field Theory and what it says about subatomic particles. I've read that QFT regards particles as excited states of underlying quantum fields. If this is the case, how can particles be regarded as objective? It seems to me that this also removes some of the...
  18. J

    Angular momentum of two particles connected by a rigid bar

    Lets do it for the left (the right will be similar): ##r_{left}=[(L-a\sin\theta)\sin\phi,(L+a\cos\theta)\cos\phi]## so ##v_{left}=[-a\dot{\theta}\cos\theta\sin\phi+(L-a\sin\theta)\dot{\phi}\cos\phi,-a\dot{\theta}\sin\theta\cos\phi-(L+a\cos\theta)\dot{\phi}\sin\phi]##. Is this right?
  19. FireAP

    Point sized particle collision and no transfer of energy

    Two identical point-sized particles with the same Y-coordinate were traveling along the X and Z axes respectively. Given that gravity is acting parallel to the Y-axis, will the particles when they eventually collide, continue traveling along the same linear path due to work done by either being 0?
  20. rachelmaddiee

    Chemistry Determining Moles and Particles from Mass of a Compound

    mass = 37.2 g AICI3 (given) number of ions = AI3+ Ions (unknown) number of ions = CI- Ions (unknown) mass = g/formula unit AICI3 (unknown) The ratio of AI3+ Ions to CI- Ions is 1:3 Molar Mass AICI3 (1 x 26.98 g/mol AI) + (3 x 35.45 g/mol CI) = 133.33 g/mol AICI3 molar mass = 133.33 g/mol...
  21. dRic2

    I Exclusion principle and the distance between two particles

    Hi, I'm reading the book "Quantum theory of many-particle system" by Fetter and Walecka. I can not understand the following quote from the book: Ok so the first thing I don't quite get is the part about the correlation function. I've tried to Google it a bit but didn't find anything which I...
  22. S

    Number of Angular Momentum States (3 particles)

    I can solve the two particle system easily enough: Using ##j_1 = 1## and ##j_2 = 1##, the possible total angular momentum values are ##j = 2, 1, 0##. With ## m = -j , -j+1, ..., j ##, ##j = 2: m = 2, 1, 0, -1, -2 ## (5 states) ##j = 1: m = 1, 0, -1## (3 states) ## j = 0: m = 0 ## (1 state) I...
  23. ilper

    I The construction of particles in QFT

    In all books about QFT I have seen I can not find anything about what a localized particle concept is. Suddenly I found this note in Zee's 'QFT in nutshell' page 4: "As usual, we can form wave packets by superposing eigenmodes. When we quantize the theory, these wave packets behave like...
  24. H

    Necessary KE of particles to create a resulting particle in a collision

    So I am making the assumption that the resulting particle Z is emitted at rest. For part a I believe that since the two positron beams are symmetric they would each provide half of the energy to create the Z particle so the KE of each positron would be 91.187GeV/2, I am ignoring the rest energy...
  25. H

    I How did the initial dust particles form?

    I've looked for a while and can't find an answer to this, hence the post. Ultimately this is a question about how the first pieces of "classical" matter formed from quantum matter. My study of self-organizing systems shows that you need a hierarchical build-up of structures to allow a complex...
  26. Riotto

    I Single-particle phase spaces for a system of interacting particles

    For a system of interacting particles, is it possible to define single-particle phase spaces? If not, why?
  27. Purahei

    Fortran Discrete Element Method in FORTRAN 90 for collisions of particles

    Does anyone know a simple implementation in FORTRAN 90 of collisions of particles?
  28. F

    I Why in BEC we must separate number of particles of ground state?

    In BEC, why do we separate the number of particles of ground state(E=0) from the integral(total number of particles) when temperature below critical temperature. Why is the overall integral wrong while the index of sum of number of particle can be considered as continuous? Is it correct that...
  29. nmsurobert

    B Can elementary particles truly be at rest in an E field?

    I'm working on E fields and particles in E fields, and I was wondering if particles are ever truly accelerated from rest. I did some reading on how accelerators work and cathode tubes, but it seems that particles are always in some type of motion. Is this just a thing for introductory level...
  30. M

    I Even/Odd solutions for particles in boxes

    My book tells me that, for both infinite and finite particle in boxes, that: Even solutions are for n = 2, 4, 6, etc and have a sin function form, while odd solutions are for n = 1, 3, 5 etc and have a cos function form. I'm very confused though, because sin functions are odd and cosine...
  31. Ranku

    I Energy momentum of massless particles

    Before electroweak symmetry breaking, there were massless particles. Can these massless particles be seen in terms of energy momentum relation ##E = ##c##p##?
  32. Diracobama2181

    A Four spin 1/2 particles at the Vertices of tetrahedron

    For a tetrahedron with four spin (1/2) particles, I know there are three separate energy levels at $$l=2,l=1,and l=0$$. My question is how I would go about finding the degeneracy of each level. I know that the number of states must be $$2^4$$. Any clues on where to start would be appreciated...
  33. kmm

    Particle Is Griffiths Introduction to Elementary Particles up to date?

    I have a copy of Griffiths Introduction to Elementary Particles (1st Edition) and was thinking of beginning to work through it. I was curious if anyone knows if this text is sufficiently up to date or if there have been any major developments in particle physics that would make it worth getting...
  34. X

    I Giving mass to other particles?

    Higgs bosons are very heavy particles (probably 1000 times heavier than a protons) and very unstable. Now we can create them in particle accelerators like LHC, like countless of other particles. But wait. This one can give mass to particles without mass, does this violate the conservation of...
  35. mastrofoffi

    Interaction energy between nonpolar particles

    I tried an approach where I build the interactions one by one and then add them all to find the total potential energy. The electric field of particle 1 induces a dipole moment on particle 2 given by ## \mu_2 = \alpha_2 E_q(2) ##(by ##E(2)## I mean the field evaluated at the position of particle...
  36. jackmiller2003

    I Time Delay Information Transfer with Entangled Particles

    Hello, my name is Jack and I'm a year 11 student in Australia. After listening to, and reading some information regarding quantum entanglement, I'm still a little unsure about the solution to a thought experiment: Let's say that I create a situation in which multiple pairs of particles are...
  37. P

    I Proton & Electron Speed in Stars: What You Need to Know

    How fast are protons and electrons moving within a star?
  38. J

    I Can two particles be in the same place at the same time?

    Can two particles ever be said to occupy exactly the same space at the same time while remaining distinct objects?
  39. R

    A Effect of High-Energy Particles on Lead

    Neil Comins in The Hazards of Space Travel states a 40-inch thick wall of lead would be needed to shield interplanetary travelers from the solar wind, coronal mass ejections, and cosmic rays. When lead is constantly bombarded with high energy charged particles, what changes occur to the lead?
  40. bob012345

    A What is the solution for two electrons on a sphere?

    The Quantum Mechanical solution for a particle on a sphere is well known. I'm looking for a treatment of two particles on a sphere where both particles are electrons. I assume it's analytically solvable. Of course, I am not expecting someone to actually solve it from scratch (unless you want to)...
  41. Michael Price

    A Gauge breaking and Faddeev-Popov ghost particles

    Summary: In QFT, if we add a gauge breaking term to the Lagrangian, do we still need to introduce Faddeev-Popov ghost particles? Ghosts seems to be introduced to maintain gauge invariance. But suppose we have eliminated the gauge invariance, from the start, by explicitly introducing a gauge...
  42. Ranku

    B Understanding Virtual Particles: Speed and Rest Mass

    Do virtual particles travel at the speed of light, or do they have 'virtual rest mass'?
  43. J

    B Why do photons only interact with charged particles?

    Why do photons only interact with charged particles?
  44. A

    Quantum numbers of a system of particles

    Hello everybody! I have a problem with this exercise when I have to find the possible angular momentum. Since ##\rho^0 \rho^0## are two identical bosons, their wave function must be symmetric under exchange. $$(exchange)\psi_{\rho\rho} = (exchange) \psi_{space} \psi_{isospin} \psi_{spin} =...
  45. H

    I Would distinguishable particles experience bonding?

    The book explains covalent bonding is due to exchange forces of attraction, which isn't a real force but the last term in [5.22]. This term arises due to electrons being indistinguishable particles. If electrons were distinguishable, there would be no exchange forces. Then, would there still be...
  46. S

    B What Are Quantum Fields and How Do They Relate to Particles?

    The summary, erm, sums it up. I just can't wrap my head around "probability." ...Does space even exist? And the field thing I'm really half-remembering. I read somewhere particles are vibrations in fields, or fields bumping into each other, or something. What's a field?
  47. danyull

    Internal Energy of a Mole of Particles each with 3 Energy Levels

    Hello, I'm doing some refreshers before going back to school. Stat mech is my shakiest and I'd appreciate some help on this problem. I know that for a single particle, the partition function will be $$Z = 1 + 2e^{-\beta\Delta} + 2e^{-4\beta\Delta}$$ and so its internal energy is $$\frac{1}{Z}...
  48. E

    Spin-0 Particles: Help Understanding Test Process

    I actually have 0 clue how to approach this. I'm thinking this might have to do something with the Stern-Gerlach experiment, but I don't know how that would help me test a spin-0 particle. If anyone could please help me with this, that would be great!
  49. Alfredo Tifi

    Synchrotron Radiation: Charge Loss of Relativistic Particles in Magnetic Fields

    Problem Statement: It is possible to describe synchrotron radiation as caused by a loss of electrical charge of relativistic particles that are moving in a magnetic field? Relevant Equations: E = mc2 An Italian expert of black hole M87 (Elisabetta Liuzzo) explains that the expected axial...
  50. B

    A Are unstable particles ever really external lines in QFT?

    Let's for example consider the Z boson. It can't directly be detected; so is it ever really correct to draw it as an external line on a Feynman diagram? I've seen processes involving it before be written as something -> Z + something, then Z -> ... but since unstable particles aren't really on...
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