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. N

    I Particle has certain energy levels in a potential well?

    In the 'Particle in a box' system, with the well being extremely narrow, why does the particle path have to follow certain energy levels compared to the classical system? Thanks in advance.
  2. STAR GIRL

    What is smallest particle in an electron or a quark?

    What is smallest particle in an electron or a quark?
  3. F

    I Can a particle cause a Bose-Einstein condensate to wave?

    Could a particle move through and displace a Bose-Einstein condensate, causing it to wave?
  4. MrDickinson

    B Question about time and particle interactions

    First, I am new to physics and only taking my first course in calculus based classical mechanics with topics covering thermodynamics and an introduction to general and special relativity. Everything here is pretty much a question, even if periods exist and not question marks. My teacher had...
  5. K

    I Stoke's equation -- particle size

    I want to solve stokes eq. for particle diameter in um size. Do i have to change the units to make them uniform. please help in solving the eq. by plugging these numbers. velocity= 50 mm/h Particle density= 2650 kg/m^3 Medium density= 1000 kg/m^3 viscosity = 1.002 mPa Gravity= 9.8 m/s^2
  6. deuce123

    I Particle accelerator question -- when the protons "crash" particles are created

    I'm not sure if this is the right place for this question., but I'll ask anyways. So in particle accelerators when the protons "crash" particles are created because of the extremely high amount of energy(example of e=mc^2?)? Is that correct? Also, where do these particles come from? The Higgs...
  7. Gary Smith

    B What is the smallest particle which can be visually observed

    What is the smallest particle which can be visually observed with a microscope?
  8. Lunct

    B Can a particle be in two entanglements at the same time?

    Can one particle be entangled with multiple particles at the same time? Let's say we have particle A, and particle B, then particle C. Can particle A be entangled with particle C and B at the same time? Sorry if this is a stupid question.
  9. F

    Direction of magnetic field and moving particle

    Homework Statement A particle of mass 0.195 g carries a charge of -2.50 x 10-8C. The particle is given an initial horizontal velocity that is due north and has magnitude 4.00 x 104 m/s. What are the magnitude and direction of the minimum magnetic field that will keep the particle moving in the...
  10. S

    I Publications in Particle Physics

    Hello! I read several times that those at CERN observe a new particle with a precision of 3-3.5 sigma and overnight (more or less) hundreds of papers in theoretical physics appear explaining the role of that particle and all its physics implication and after a while CERN announces that there was...
  11. A

    B Fusion and Alpha Particle Emission: Neutron vs Proton

    When two deuterons fuse, I understand they form an alpha particle in an excited state. Based on mass differences the fusion releases 23.85MeV, which is enough to eject a proton (19.81MeV) or a neutron (20.58MeV) from the alpha particle. It seems to prefer neutron emission, as this fusion is used...
  12. Alexanddros81

    Pytels Dynamics 12.14: particle moves on helix

    Homework Statement When a particle moves along the helix shown, the componentsof its position vector are x=Rcosωt , y = Rsinωt , ##z=-\frac h {2π} ωt## where ω is constant. Show that the velocity and acceleration have constant magnitutes, and compute their values if R=1.2m, h=0.75m, and...
  13. arpon

    I Is the Dimensionality of Vector Spaces the Same for Different Quantum States?

    Consider the particle in a box problem. The number of energy eigenbasis is 'countable' infinity. But the number of position eigenbasis is 'uncountable' infinity. x can take any value from the interval [0,L] Whichever basis I choose, shouldn't the dimensionality of the vector space be the same?
  14. A

    Bombardment of Nitrogen-14 with an alpha particle

    Question: When alpha particles, having kinetic energy 3.0000 MeV bombard nitrogen-14 nuclei, oxygen-17 forms and the reaction releases a proton. Calculate the kinetic energy shared by the reaction products. Nitrogen-14 = 14.000307 amu Helium-4 = 4.00260 amu Oxygen-17 = 16.99913 amu Proton =...
  15. P

    Particle accelerators and timing for particles

    So, I found this document that talks about rf cavities at lhc https://home.cern/about/engineering/radiofrequency-cavities Can you please explain me what i underlined Means? If i understood when the particles achieve the velocity the scientist want them to achieve they get into the cavity when...
  16. H

    I How a particle localized in half of a box changes over time

    I think the answer is incomplete, because proving that ##\psi(x)## isn't stationary doesn't prove that the particle isn't localised, it doesn't prove that ##\psi(x)\neq0## at ##0<x<\frac{a}{2}## at some later time. ##\psi(x)## could always be changing on the left side of the box (say from a...
  17. Dadface

    I Is Wave-Particle Duality Still Relevant in Modern Physics?

    https://www.nature.com/search?journal=nphys&q=wave%20particle%20duality&page=1 When people come to this forum enquiring about the concept of wave particle duality the usual advice seems to be based on the idea that the concept is outdated and has historical interest only. The problem is that...
  18. H

    I Why is E not equal to p^2/2m for a particle in a box?

    Consider a particle in the ground state of a infinite well with sides at ##x=0## and ##x=a##. The ground-state energy ##E_1=\frac{\hbar^2\pi^2}{2ma^2}##. The energy of the particle is entirely kinetic. Hence, ##E_1=\frac{p^2}{2m}##. Solving for ##p##, we get ##p=\pm\frac{\hbar\pi}{a}##. So the...
  19. H

    A Understanding the Relativistic Action for a Point Particle

    The action for a relativistic point particle is proportional to the infinitesimal invariant length ds. Is there some more intuitive explanation for this? The action is defined by taking the time intergal over the difference between the kinetic energy and the potential energy. So how does this...
  20. D

    Momentum of W Bosons After Collision in Particle Physics Lab

    Homework Statement In a particle physics lab, an electron e− and a positron e+ collide, annihilate, and produce a W+ boson and a W− boson. Just before the collision, the electron and positron have a total energy of E = 100 GeV each, with velocities pointing along the +x-axis and -x-axis...
  21. P

    A site that explains the physics behind particle Accelerators?

    Please, can you give me a site where the physics of particle accelerators is explaimed with numbers and equations to high school Level? I found the site of the department of Energy and the cern but there are not equations like the lorentz force and the oscillating fields... I need something a...
  22. AdrianMachin

    Plot 3D graph of electric potential of a charged particle

    Homework Statement Plot the electric potential ##V(r)## due to a positively charged particle located at the origin of an XY plane. Homework Equations ##V=\frac 1 {4πε_0} \frac q r## The Attempt at a Solution I'm unfamiliar with 3D coordinates at this time, but I like to know how can I plot it...
  23. G

    A What does a CPT transformation do to particle properties?

    If I have a particle with: Momentum: p Spin: s Energy: E Position: x Time coordinate: t Charge: q And I preform a CPT transformation on said particle, what will these variables become? Can you show me mathematically? Also, could you show me how this effects the wavefunction/quantum state of...
  24. J

    I Smallest possible orbit and velocity of a particle?

    If the units of angular momentum are quantised in integer amounts of ##\hbar##, does that then imply that we have restrictions on the smallest possible radius ##r## of an orbit of a given mass ##m##, given that the speed of light is ##c##. As follows, $$\hbar=m\bf{r}\times \bf{v}$$, where v is...
  25. Pete Moore

    Particle Reynolds number / max entrained particle size

    I am not a student; this is for work. Would some kind soul: a) direct me to an online calculator to enable answering the following or b) give me the answer and show how you arrived at it :) or c) advise me of the formula / process by which I can arrive at the answer? THANK YOU! What is the...
  26. S

    Kinetics of System Particle/ Pulley system with masses and i

    I can't seem to solve it, considering inertia can someone please solve it, both of the following question in the given picture. I would be very much thankful.
  27. DarkBabylon

    I A particle measured in a too high potential

    Hello, we were introduced to qunatum physics this semester. We were tackling the problem of particles sent with a certain value of energy into a potential well as well as a barrier. The not so very new thing to me was that the probability is non zero in places where the potential is higher. In...
  28. M

    I Particle antiparticle creation

    When a particle and antiparticle pair is created are they created on the same position? If they weren't in the same position it would lead a problem on energy conservation, but they are fermions so they shouldn't be on the same position in space.
  29. S

    What is the energy of the alpha particle and recoiling nucleus?

    Homework Statement The Q-value of alpha decay of Pu-239 is 5.244 MeV. Calculate the energy of the alpha particle in MeV. Calculate the energy of the recoil nucleus decay product in MeV. (answer correct to 3 decimal places) Homework Equations The Q value of a nuclear reaction is the difference...
  30. F

    I Does a particle and its anti-particle always annihilate?

    When a particle and its corresponding anti-particle interact do they always annihilate or are there other possible interactions that can occur, such as them scattering off of one another? If the former is true, why do they always annihilate? If the latter is true, is it the case that the most...
  31. H

    Calculating the equations of motion for particle in parabola

    I made the problem up myself, so there might very well not be a rational answer that I like! Homework Statement A point-particle is released at height h0 is released into a parabola. The position of the particle is given by (x, y) and the acceleration due to gravity is g. All forms of friction...
  32. Toby_phys

    Lorentz force - particle in an odd magnetic field

    Homework Statement Particles of mass ##m## and charge ##q## are initially traveling in a beam along the ##z## direction with speed ##v## when they enter a long magnetic quadrupole lens, where there is no E-field and the magnetic flux density is ##B = Ay\hat{i} + Ax\hat{j}##, and where A is a...
  33. W

    Velocity of particle leaving wedge

    Homework Statement In the given figure, a wedge of mass 2m is lying at rest on a horizontal surface. The wedge has a cavity which is the portion of a sphere of radius R. A small sphere of mass m is released from the top edge of the cavity to slide down. All surfaces are smooth.Prove the maximum...
  34. L

    Decay rate of a particle into three particles

    Homework Statement Consider the process of decay of a muon into one electron, one electron antineutrino and one muon neutrino using the Fermi theory. Assume the matrix element is, ignoring the electron's and the two neturino's masses, |\mathcal{M}|^2 = 32G_F^2(m^2-2mE)mE being E the electron...
  35. B

    I Hamiltonian for spin-1/2 particle in B-field: units issue

    Take a spin-1/2 particle of mass ##m## and charge ##e## and place it in a magnetic field in the ##z## direction so that ##\mathbf B=B\mathbf e_z##. The corresponding Hamiltonian is $$\hat H=\frac{eB}{mc}\hat S_z.$$ This must have units of joules overall, and since the eigenvalues of ##\hat S_z##...
  36. A

    Schools What is the best for an experimental particle physicist?

    I'm interested to become an experimental physicist particularly in particle physics. I have the chance to pursue a double degree. what is the best choice that will help me more in my future career.- a double degree in physics and computer science or a double degree in physics and material...
  37. B

    I New Way of Particle Accelerating?

    Question 1: Current particle accelerators are only able to speed up particles up to around 0.16c. However, in nuclear reactors, radioactive nuclei release subatomic particles, i.e. electrons, at more than 0.75c. To increase efficiency and perhaps to observe how particles collide at high speeds...
  38. LouysHong

    I Launching a particle at the highest point inside a sphere

    If a smooth sphere with radius a is fixed on a plane, and a particle is projected horizontally at the highest point outside/on of the sphere with speed (4ag/5)^0.5, I know that the particle will lose contact with the sphere when it makes an angle of theta with the upward vertical, where theta is...
  39. kipinaac

    I What does it mean for a particle to vibrate?

    I intuitively understand macroscopic vibration, but trying to understand what it means for a particle to vibrate doesn't seem to make sense from the classical understanding I have of momentum and energy. First, are particles even said to vibrate or have vibrational energy? If so, how is momentum...
  40. G

    Probability Density in an infinite 1D square well

    Homework Statement The wave function of a particle of mass m confined in an infinite one-dimensional square well of width L = 0.23 nm, is: ψ(x) = (2/L)1/2 sin(3πx/L) for 0 < x < L ψ(x) = 0 everywhere else. The energy of the particle in this state is E = 63.974 eV. 1) What is the rest energy...
  41. Albi Mema

    Consider Compton scattering of a photon by a moving electron

    Homework Statement Consider Compton scattering of a photon by a moving electron. Before the collision the photon has wavelength λ and is moving in the +x-direction, and the electron is moving in the −x-direction with total energy E (including its rest energy mc2). The photon and the electron...
  42. LarryS

    B Do wave packets really represent a free particle?

    Given a source of electrons, like from an electron gun. Physicists call these freely traveling particles and often use a Gaussian wave packet to represent them with the group velocity being precisely defined as the velocity of the center of the packets. But if we do not measure the position of...
  43. W

    I How to calculate particle size from a peak list?

    Hi guys, I want to calculate the size of nanoparticles by using data from a peak list obtained from the use of XRD. Can anybody help me calculate the particle size by using the scherrer equation? Thanks! :)
  44. A

    I Can the energy of a particle ensemble in QFT be bounded over time?

    Hi all, Question for which .I feel silly asking - but since I'm still learning: A particle state in QFT is considered to be an asymptotic state with a well defined energy. Now, if I take an ensemble of particles after a very large number of interactions (say, e.g., a macroscopic object like a...
  45. Dadface

    I Why does "wave particle duality" not exist anymore?

    I think I've asked this question here before but I'm still not clear about the answers. To reiterate, some experts on this forum seem to be of the opinion that wave particle duality doesn't exist anymore and this has been expressed in different threads and in different ways with certain...
  46. davidge

    B "Distribution" of a particle in different situations

    I was thinking about the "distribution" of a particle in space in different situations. An electron bound in a atom have a wave function that is broad. What about the broadness of the wave function of conduction electrons in a wire? Or doesn't it even make sense to quantum-mechanicaly speak of...
  47. J

    I How do we measure the EM field that a particle produces?

    [Moderator's note: posts from several threads on the same topic have been merged into this thread.] When we measure the EM field of a charged particle, what exactly are we measuring? Are we measuring the position of the EM field, the strength of it, what? Does a penning trap measure the EM...
  48. H

    I Energy and states of a particle in a box.

    Suppose we have a classical particle in box. The number of degrees of freedom is 6. The position of the particle and its momenta. Now if we want to calculate the entropy of the system as a function of the energy we only need to find a relation between all the possible states the particle can be...
  49. EnumaElish

    News Ancient particle accelerator discovered on Mars

    "The search for water, or even signs of life, on the planet Mars has been ongoing for some time. But with today’s announcement by CERN and NASA scientists, the exploration of the red planet has revealed a major new discovery. New images of the surface of Mars taken by NASA’s Mars Reconnaissance...
  50. E

    In which direction a spherical particle moves under torque?

    Consider a small rigid spherical particle of radius a, fully immersed in a viscous incompressible Newtonian fluid of shear viscosity η above a hard-wall with stick (no-slip) boundary conditions, located at the plane z = 0. A constant positive (external) torque Tx is applied on the particle. My...
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