What is Particle: 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

    I Particle Physics and Quantum Mechanics

    I’m having a hard time, as I begin learning QM, knowing what it applies to, if I can put it that way. Is QM the rules that describe how the particles of the Standard Model interact with each other? Or what is the best way to understand the relationship between what one studies when one studies...
  2. Sorcerer

    Uncharged particle in a magnetic field suddenly gets charged

    What happens to the velocity? Say we have a piece of space debris in free fall. It has a particular velocity at a given time. Then say at some later time it's bombarded with ionic gas or something that causes it to become charged. Does the velocity change? My guess would be yes, because the...
  3. S

    I Particle acceleration and kinetic energy

    Hi, I was reading about magnetic reconnection in astrophysical plasma and it says that magnetic reconnection transforms magnetic energy into heat via ohmic dissipation, particle acceleration and kinetic energy. It is not clear to me the difference between particle acceleration and kinetic...
  4. C

    I Phenomenological potentials and exchange of force carriers

    Consider a proton-neutron system. Phenomenlogical nucleon-nucleon potentials contain exchange forces terms (Majorana, Bartlett and Heisenberg terms), which are linked to the symmetry of the state w.r.t. (for example) the exchange of isospin (i.e. charge). On the other hand proton and neutron...
  5. C

    I Are resonances formed in the scattering of a baryon and a meson?

    Consider the following reaction of strong interaction (in a scattering process) $$n+\pi^+\to \Lambda_0+K^+\tag{1}$$ Then the particle ##\Lambda_0## formed decays with weak interaction $$\Lambda_0\to \pi^+ +p\tag{2}$$ For each decay process I measure the four momenta of ##K^+##, ##\pi^+##...
  6. C

    I De Broglie relation using four momentum in particle physics

    In particle phyisics four-momentum is used and De Broglie relation is used to understand what lenghts can be "seen" in an experiment. Here (page 6) https://people.phys.ethz.ch/~pheno/PPP/PPP2.pdf it is claimed Where ##Q^2## is not actually "momentum" but its the square of the four momentum...
  7. C

    I Does strong force increase or decrease with aligned spins?

    The deuterium exists only with the proton and neutron of aligned spin, which suggests that the residual strong force is greated with aligned spins, i.e. the binding energy is greater if the spins are aligned. On the other hand the mass of ##\Delta^{+}## is greater than the mass of proton ##p##...
  8. Vicol

    Hamilton-Jacobi equation and particle-wave motion

    I've seen somwhere a claim that Hamilton-Jacobi euqation is the only formulation of classical mechanics which can treat motion of particle as wave motion. There was something about hamilton prinicpal function, hamilton characteristic function and one of these change in time like wavefront or...
  9. platosuniverse

    B Why doesn't the plate interact with the particle in double slit?

    When particles are shot at the plate/screen in the double slit experiment, why doesn't the particles interact with the screen? Shouldn't the plate act as an observer and "collapse" the wave function into one or the other slit? Why does it take a measuring apparatus to know which slit the...
  10. A

    I How Long Does a Particle Stay in a Quantum Potential Well?

    Let's suppose I have a potential well: $$ V(x)= \begin{cases} \infty,\quad x<0\\ -V_0,\quad 0<x<R\\ \frac{\hbar^2g^2}{2mx^2},\quad x\geq R \end{cases} $$ If ##E=\frac{\hbar^2k^2}{2m}## and ##g>>1##, how can I calculate how much time a particle of mass ##m## and energy ##E## will stay inside...
  11. L

    I Shock crossing probability for isotropic particle flux

    Hi there, I am currently trying to understand the theoretical frame work of diffusive shock acceleration. I am having trouble understanding a step in the derivation given by drury 1983 (http://www.oa.uj.edu.pl/user/mio/Ast-Wys-En/Literatura/drury.pdf). In the derivation of eq. 2.47 it is stated...
  12. R

    Viewing Particle P in a Cylindrical Vessel - 40 cm Height Needed

    I1. Homework Statement A cylindrical vessel whose diameter and height both are equal to 30 cm is placed on a horizontal surface and a small particle p is placed in it at a distance of 5 cm from the centre. An eye is placed at a position such that the edge of the bottom is in the plane of...
  13. G

    What is the solution for particle motion between two masses?

    Homework Statement Statement of the problem (quoting from my assignment): a) write equations of motion b) try to solve analytically Given: m1, m2 - two masses R - distance between two masses Homework Equations V=-G(m1/r + m2/(R-r)) F=-dV/dr The Attempt at a Solution a) Equations of motion: v...
  14. L

    Programs SISSA theoretical particle physics

    I have thought about taking the enterence exam for theoretical particle physics at SISSA this coming July. I was hoping someone here took it in a previous year and could give me some advice. By looking at the old written exams, it seems they are mainly made up from QFT and QM. So my plan was...
  15. CDL

    I Quantum Scattering Differential Probability

    I am reading Griffiths' Introduction to Quantum Mechanics, specifically the chapter on scattering. He is discussing the scenario where an incoming beam of particles scatter off an azimuthally symmetric target. At large separation ##r## from the scattering centre, the wavefunction for incoming...
  16. K

    B Photon particle independent of wave question

    A photon acts like a wave and a particle. In the double slit experiment the photon seemingly interferes with itself which is troublesome to me. To help better understand this, I would rather think of the photon as a particle and the wave as something that is independent of the photon where the...
  17. J

    Higgs Experiment for new particle (decay widths)

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Question: An experiment is proposed to directly measure the width (Γ) and mass (m_H) of the Higgs boson via the reaction: muon+ + muon- > H. Sketch a graph of the expected cross section as a...
  18. Abhishek11235

    Trajectory of a particle under the given force

    A particle of mass m in xy plane is attracted toward the origin with the force $$\begin{align}\vec{f} = - \frac{k^{2} m}{r^{6}}\vec{r}\end{align}$$ where ##\vec r## is position vector of particle measured from origin. If it starts at position ##(a,0)## with speed $$v=\frac{k}{\sqrt{2} a^{2}}$$...
  19. Cocoleia

    Particle decay, Lorentz transformations with angles

    Homework Statement I have a mother particle at rest, which decays to a daughter particle. The daughter has mass m, momentum p and energy E and is at an angle θ1. Now I have to assume that the daughter is emitted at an angle θ2, and the mother is moving along the x-axis with velocity βc. I need...
  20. BookWei

    Field strength tensor for a moving charged particle

    Hi, I am studying Chapter14 in Jackson. My attached file is about field strength tensor. My question is how can I obtain the radiation and the non-radiation terms in the field strength tensor for a moving charged particle. Many thanks.
  21. renec112

    Free particle: expectation of x for all time with Ehrensfest

    Hello physics forums. I'm trying to solve an old exam question. Would love your help. Homework Statement A free particle in one dimension is described by: ## H = \frac{p^2}{2m} = \frac{\hbar}{2m}\frac{\partial^2}{\partial x^2}## at ##t = 0## The wavefunction is described by: ## \Psi(x,0) =...
  22. Isaac0427

    B Double slit and wave particle duality

    Just for my knowledge, not to confuse the OP, why would you say, for example, the double slit experiment does not show both of these properties in one measurement method? [Mentors' more: this thread was forked off from another thread]
  23. Lami

    Particle acceleration/displacement question

    Homework Statement A particle moves in the x-y plane relative to a fixed point O. Initially, the particle is at the point 6i-2j, where I and J are position vectors in the directions of the x and y-axis respectively. The particle moves such that t seconds after the start of its moition, the...
  24. renec112

    Probability distribution momentum for particle

    Homework Statement A particle with mass m is moving on the x-axis and is described by ## \psi_b = \sqrt{b} \cdot e^{-b |x|}## Find the probability distribution for the particles momentum Homework Equations ## \Phi (p)= \frac{1}{\sqrt{2 \pi}} \int_{-\infty}^\infty \Psi(x,0) \cdot e^{-ipx} dx##...
  25. Islam Hassan

    I Hawking Radiation and the Negative Energy Particle

    The following from Wiki re Hawking Radiation:“... vacuum fluctuations cause a particle–antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole while the other escapes. In order to preserve total energy, the particle that fell into the...
  26. T

    B What, in essence, distinguishes light from matter?

    Before quantum mechanics, light was generally seen as a wave and matter as particles (biliards). From e.g. the discovery of the photoelectric effect, one saw that light can also be seen as a particle. From e.g. the double slit experiment, one makes the interpretation that matter can also be seen...
  27. PKM

    How to find the Trajectory of a Particle

    Homework Statement The velocity of a particle at a certain point is given as \vec v=5(y\hat i - x\hat j). How to find the general equation of the path of the particle? Homework Equations Here, \frac{d\vec x}{dt}=5(y\hat i - x\hat j). The Attempt at a Solution As the velocity is not given as a...
  28. hilbert2

    A How Does a Particle's Energy State Change in a Non-Uniform 2D Corridor?

    Suppose we have a particle of mass ##m## moving freely in the xy-plane, except for being constrained by hard walls to have ##-L/2 < y < L/2##. Now, the energy eigenstates would be something like ##\psi (x,y) = C \psi_x (x) \psi_y (y) = C e^{-ikx}\cos\left(\frac{n\pi y}{L}\right) ##, where...
  29. isukatphysics69

    Using potential energy graph, find particle turning point

    Homework Statement Homework Equations Emec - PE = KE The Attempt at a Solution When particle starts at x = 4 KE = .5(.25)(225) = 28.125 Energy of system = 28.125 I don't have anything with position here so i am unsure how to find what position that the energy will be equal to the Emec and...
  30. E

    Need help finding angular momentum of a particle

    1. At the instant of the figure, a 6.70 kg particle P has a position vector of magnitude 4.30 m and angle θ1 = 43.0° and a velocity vector of magnitude 3.40 m/s and angle θ2 = 32.0°. Force , of magnitude 7.40 N and angle θ3 = 32.0° acts on P. All three vectors lie in the xy plane. About the...
  31. R

    I What does this equation for a free particle mean?

    So there's a free particle with mass m. \begin{equation} \psi(x,0) = e^{ip_ox/\hbar}\cdot\begin{cases} x^2 & 0 \leq x < 1,\\ -x^2 + 4x -2 & 1 \leq x < 3,\\ x^2 -8x +16 & 3 \leq x \leq 4, \\ 0 & \text{otherwise}. \end{cases} \end{equation} What does each part of the piecewise represent...
  32. I

    A particle P2 chases particle P1 with constant speed.

    Homework Statement [/B] A particle P1 moves with a constant velocity v along x-axis, starting from origin. Another particle P2 chases particle P1 with constant speed v, starting from the point (0, d). Both motion begin simultaneously. Find - 1. Initial acceleration of P2. 2. Ultimate...
  33. L

    Particle The need for getting another particle physics book

    Hi there, my name is Leon and I am a physics undergraduate. Recently I decided to dig into the field of particle physics by getting some related books. I definitely will get some books on quantum field theory (Peskin, Scrednick, mandl and shaw...etc), since qft is a framework of particle...
  34. N

    Velocity of a charged particle as it approaches infinity

    Homework Statement Homework Equations F = k(q1q1/r^2) K = (mv^2)/2 The Attempt at a Solution I got number 18 easy enough, number 19 seems simple but I'm not getting the right answer. I'm calculating Force exerted by each charge on the new charge using F = k(q1q1/r^2) for the three charges...
  35. J

    B Exploring the Potential of a Particle Near a Black Hole

    Could a particle near a black hole about to enter rid the string of its vibration?
  36. T

    Kinetic energy of an alpha particle

    Homework Statement During the ##\alpha## decay of ##^{238}_{92}U## an ##\alpha## particle is fromed inside the nucleus. Given that the last 4 nucleons in ##^{238}_{92}U## have an average binding energy per nucleon of ##6.1MeV##, estimate the kinetic energy of the ##\alpha## particle when it is...
  37. Kenneth Boon Faker

    B The Nature of Reality: Understanding the Behavior of Subatomic Particles

    A subatomic particle can either be a wave or a particle. When it is a particle, what actually is it? is it literally like a tiny physical ball rattling around? (If not, then what is it?) And when it is a wave, what is it? From my understanding, when a particle behaves like a wave, the...
  38. S

    Charged particle motion in a magnetic feild

    Homework Statement A particle moves along a circle in a region of uniform magnetic field of magnitude B=4.0 mT. The particle is either a proton or an electron. It experiences a magnetic force of magnitude 3.2x1015 N. What are (a) the charge of the particle? (b) The particle speed? (c) The...
  39. G

    Ultra-Relativistic Particle Decaying to Identical Particles

    Homework Statement Show that it is impossible for an ultra-relativistic particle with ##pc>>Mc^2## to disintegrate into two identical massive particles of mass m. Homework Equations Conservation of four momentum The Attempt at a Solution The four momentum of the ultra-relativistic particle...
  40. B

    I Superposition of particle identities

    Suppose a neutral meson decays into an electron and a positron. Are the two particles entangled as they fly apart? Before any measurement takes place, are the particles in a mixed superposition as to which one is the electron, and which one is the positron? Is there a way to test for such...
  41. J

    I Particle Desert and New Physics

    Is it possible there is a particle desert where there are no new particles between the weak and Planck scale yet there is new physics before the Planck scale.. can you give examples how this can occur? An example. If we can distinguish quantum interpretations.. won't this be new physics that...
  42. T

    Wave Particle Duality For Electrons and Photons

    Homework Statement Discuss the concept of the wave-particle duality for electrons and photons and include an equation which connects the wave like and particle like properties. Homework EquationsThe Attempt at a Solution So I am having trouble with how to word this question and generally...
  43. Kenneth Boon Faker

    B Subatomic particles and the observer

    I have read that when an electron is observed, it behaves differently to when it is not being observed. Could someone please expand on this, or indeed correct me. In what way does an observed particle behave differently to a particle that isn't being observed by somebody's consciousness?
  44. S

    Lagrangian for a particle moving in x-y plane in a constant B-field

    Homework Statement Not sure if the link is showing. But it's imgur.com/a/LEvd0 Homework Equations The steps I've taken so far as written in the attempt section below is correct. The solution provided then proceeds with letting ##z = x + iy## and setting ##\ddot z+i \omega \dot z = 0##. Then...
  45. R

    Alpha particle approaching a gold nucleus

    Homework Statement An alpha particle approaches at high speeds a gold nucleus with a charge of 79e. What is the electric force acting on the alpha particle when it is 2.0e-17 m from the gold nucleus? Homework Equations FE=k(q1q2)/d2 The Attempt at a Solution FE=k(q1q2)/d2...
  46. Soffie

    B Why is this interaction forbidden?

    So I'v been told that this interaction : e- + e+ = mu- + e+ isn't allowed. Why not? I thought maybe because the mass of the muon is so much bigger, so would violate energy conservation, but the electron/positron could be moving relativistically and thus have enough energy. Apparently the...
  47. D

    Particle Entrainment in a Counter-Current Flow Reactor

    Hi there, I am currently looking to build a rotating kiln to provide the necessary heat/res. time/gases to react a solid feedstock. The problem that I can envision, however, is that the solid (which is fed as small particles) may become entrained in the counter-current gas flow inside the...
  48. Soffie

    B Distinguishing between interactions (decays and collisions)

    I always struggle to know which force (strong nuclear, electromagnetic, weak, gravity) is responsible for an interaction. For example, pi+ + pi- = neutron + pi0 I would say its strong force responsible, because quarks are involved. But the pions are also charged, so how do I know it's not...
  49. Ignitia

    Motion of a Charged Particle in Magnetic Field

    Homework Statement Viewers of Star Trek have heard of an antimatter drive on the Starship Enterprise. One possibility for such a futuristic energy source is to store antimatter charged particles in a vacuum chamber, circulating in a magnetic field, and then extract them as needed. Antimatter...
  50. hilbert2

    A Particle moving on a constrained path

    There seem to be many kinds of examples where the behavior of a quantum particle having been constrained to move on a curve or surface is investigated. The simplest is the case of a particle on a circular path or a spherical surface, where the energy eigenstates are equal to the angular momentum...
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