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

    Understanding Stable Particles: Neutrons, Electrons, Photons, and Neutrinos

    How can be sure than the unique stable particles are the neutrons, the electrons, the photons and the neutrinos? Couln´t it be possible than at low energies were there more particles??
  2. T

    Hamiltonian of two identical spin-1/2 particles

    Homework Statement Two identical spin-1/2 particles of mass m moving in one dimension have the Hamiltonian $$H=\frac{p_1^2}{2m} + \frac{p_2^2}{2m} + \frac{\lambda}{m}\delta(\mathbf r_1-\mathbf r_2)\mathbf s_1\cdot\mathbf s_2,$$ where (pi, ri, si) are the momentum, position, and spin operators...
  3. TrickyDicky

    Magnetic moment from neutral particles in QFT

    Could somebody take a stab at explaining how can quantum fluctuations give neutral elementary particles a magnetic moment? (in the usual explanation given by QFT textbooks, I think there are people around here denying the existence of quantum fluctuations, insert the more neutral expression...
  4. A

    Consider Two Spin-1/2 Particles

    Homework Statement Consider two spin 1/2 particles. Initially these two particles are in a spin singlet state. If a measurement shows that particle 1 is in the eigenstate of ##S_x = -\hbar/2##, what is the probability that particle 2 in this same measurement is in the eigenstate of ##S_z =...
  5. S

    Charged particles moved into a B-field

    Homework Statement Two radioactive isotopes of singly charged plutonium(Pu-249 and Pu-244) are accelerated through a potential difference of 3.00kW and enter a uniform magnetic field of 1.50T directed perpendicular to their velocities. By performing relevat calculations, show that the ratio of...
  6. TheExibo

    Electric Fields and charged particles

    Let's say there's a question where there are two charges placed, and a point in between and above the line connecting the two charges forms a triangle like this: http://session.masteringphysics.com/problemAsset/1413940/2/p19.5.jpg What would one have to do in order to find the electric field...
  7. TheExibo

    Electric Force: Charged Particles Homework Solution

    Homework Statement Particles of charge q and 3q are placed 90m away from each other. A third particle is place in between them and the total electric force on this particle is zero. Determine the position of this particle. Homework Equations F(E)=(k)(q1)(q2)/(r^2) The Attempt at a Solution...
  8. B

    Do quantum fluctuation particles create gravitational effect?

    Do particles popping in and out of existence due to quantum vacuum fluctuations create a gravitational effect? My thought is yes If so, considering all the quantum particles in existence at one time at a given moment in the universe, added to the mass of the universe as well as the mass of...
  9. Breo

    How to entangle two particles?

    I have notions of the mathematics involving (entangled state is one which is not a product state of two qubits, etc) the idea of entanglement. However, still can not figure out how to, let us say, pick a particle (which type of particle we can use as qubit? protons? electrons? ununumbiums??) A...
  10. Coffee_

    Intro to elementary particles, electron - nucleus collision

    1.Problem: An electron with energy ##E## which is much higher than its restmass collides with a much much heavier particle "A" of mass ##m## which is at rest. Find the maximal transfer of four-momentum. (Elastic collision)2. Conservation of four momentum3. Everything in natural units. So I go...
  11. G

    Are Graviton and Standard Model Particles the Only Ones in the Universe?

    How we can know that there are no more particles that graviton and standard model particles??
  12. V

    Detection of motion of non characterised particles

    I have been reading on wikipedia that dark matter is made up of a not yet characterised type of sub atomic particle. Now we know that particle energies and relative positions cannot be known with precision by Heisenberg principle but we can calculate quantities like the drift velocity of charges...
  13. Q

    Are there any particles with all the properties of a WIMP

    Are there any particles on the Standard Model of Particle Physics with all the properties of a WIMP particle(Weakly Interacting Massive Particles)?
  14. K

    Observing Particles: Is Consciousness the Factor?

    Hi Guys, I just want to put this out there. If a particle changes it's behaviour based on wether it's been observed or not what is the dividing factor? What is actually happening? Is it simply the fact that a conscious mind is watching it and because of that the particle changes its behaviour to...
  15. cseil

    Uniform circular motion for proton and 2 particles

    [Note by mentor: This thread does not use the homework template because it was moved here from a non-homework forum.] Hello, I have a problem with this exercise. I don't know if my solution is right! Could you check it, please? A proton with kinetic energy Kp is moving in a uniform magnetic...
  16. G

    Would stirring separate particles?

    Homework Statement Would stirring a fluid separate the particles? Homework EquationsThe Attempt at a Solution You stir tea to integrate the tea and the sugar so I would say that stirring would not separate the particles. Any help? Thanks!
  17. P

    S matrix and decaying particles

    Hi All, The S-matrix is defined as the inner product of the in- and out-states, as in Eq. (3.2.1) in Weinberg's QFT vol 1: S_{βα}=(Ψ−β,Ψ+α) \Psi_{±α} are the eigenstates of the full Hamiltonian with a non-zero interaction term. Can \alpha describes a neutron ? Since it is not stable, it is...
  18. S

    Moments of Inertia of two particles

    Homework Statement Two particles, each of mass m, are attached one to each end of a diameter PQ of a uniform circular disk, of mass 4m, radius a with its centre at O. The system is free to rotate about a horizontal axis through A, a point on PQ such that OA = b as indicated in the diagram...
  19. Jameson

    MHB Two new subatomic particles discovered?

    Link to article My knowledge of physics past basic mechanics is weak but as I understand the Standard Model these two new particles are combinations of other elementary particles rather than two new ones. Anyone want to expand on this article? Big news, not so big? :) Here is some discussion...
  20. M

    Length contraction of particles

    As an object moves, it is contracted in the direction of it's motion. Why wouldn't each individual subatomic particle be contracted rather than the object as a whole?
  21. A

    Find how far apart are the particles from each other

    Homework Statement Two particles oscillate in simple harmonic motion with amplitude A, about the centre of a common straight line of length 2A. Each particle has a period of 3.3 s, and their phase constants differ by π/9 rad. (Assume the lagging particle starts at +A. Also assume that the...
  22. B

    Is Virtual Wave-Particle Duality a Misconception in Quantum Mechanics?

    If there is such a thing as a virtual particle, is there also such a thing as a virtual wave? what would that actually mean?
  23. MathematicalPhysicist

    Questions from Schwinger's particles, sources and fields

    My first question from his first volume. On page 254, he writes down the action expression: (3-10.1)W=\int (dx)[K\phi+K^{\mu}\phi_{\mu}+\mathcal{L}] Where the lagrangian is: \mathcal{L}=-\phi^{\mu}\partial_{\mu} \phi +1/2 \phi^{\mu}\phi_{\mu} -1/2 m^2 \phi^2 The consideration of...
  24. kyphysics

    What Does It Mean Particles Only Have Location if Measured?

    I'm not a physics person (just an interested layperson) and have read that quantum particles don't have any location until they are measured. First, is this true? And, if so, what does that mean? For example, if you don't know where a particle exists, then how can you even measure it? And...
  25. B

    Particles with a charge passing through electric field

    Homework Statement Particles with the mass 2.6*10^(-21) kg and the charge 4 times the electron charge are fired into a homogenous electrical field made by two plates. The plates are 7.5 cm apart from each other and the voltage is 60V. Which is the least speed they need to pass through the field...
  26. J

    Does Quantum Precession Contradict Traditional Spin Directions?

    Hi pf. From what I have read, when measured, a particles spin can only be in one direction. So either 100% spinning up or 100% spinning down and not in between. So, you can't have a spin that is in between (tilted) - it must be one or the other. But I recently learned that when we place a...
  27. LarryS

    Spin 1 Particle Representations of SO(3) and SU(2)

    I am still learning about all the Groups related to the Dirac Equation for spin 1/2 particles. Apparently, the reason that the Hilbert Space for spin 1/2 particles is 2-dimensional is because when you try to map SU(2) to SO(3), the mapping is 2-to-1, i.e. SU(2) is a double cover for SO(3)...
  28. BUI TUAN KHAI

    Bmax in Bohr's calculation for energy loss of charged particles (classical case)

    Dear all, I have inquiries about the Bohr's calculation for energy loss of charged particles. These inquires are from the "Techniques for Nuclear and Particle Physics Experiments" (W.Leo). On page 23 of this book, it is written that: the the interaction time is t = b/(γv), with b is the...
  29. davgonz90

    Can Gas Particles Ever Stop Moving?

    We know that gas particles move very quickly in random motions in whatever container they are in. My question is: assuming that no gas particles ever exit or enter the container, at what point will the gas particles stop moving? From what I think I understand about the second law of...
  30. tesla420

    Variations of +/-; Can there be more than just positive and negative particles?

    Is there any evidence that suggests there can be more than just positive and negative particles
  31. X

    Do entangled particles decay simultaneously?

    I apologise in advance for my rather minimal knowledge of physics. Please assume that anything I write below is just my current understanding, and may very well be incorrect... Elementary particles decay into other elementary particles. When a a subatomic particle decays into a pair of other...
  32. K

    Entangled Particles and the Hadron Collider?

    If one was to entangle two particles and either send the two particles at each other, or send one of the entangled particles and observe the other; what do you think might happen? If there are any problems with getting an entangled particle into the Hadron Collider, please say so.
  33. nomadreid

    Assigning a Size to Particles and Strings: From Planck Scale to the Universe

    Except for associating a statistical mean to a large number of measurements, how can one assign a single point to a particle ? Indeed, how can one assign a size of anything less than the Planck scale? A similar question about strings: how can one talk about one-dimensional objects? A similar...
  34. C

    Find the Lagrangian of a System of Particles

    Homework Statement Ok, so in this system, there are two point particles of mass M connected by massless levers of length L. The pair of masses pivots about the upper point and rotates about the axis at an angular frequency ω. The lower mass is constrained to slide on the vertical axis. The...
  35. Breo

    Polarization vectors for spin-2 particles

    Who knows where this formula comes? $$ e_i \otimes e_j + e_j \otimes e_i - \frac{2}{3}( \sum_{\substack{k}} e_k \otimes e_k )\delta_{ij} $$
  36. MattRob

    Black Hole Hawking Radiation: Frame-Dependent Virtual Particles

    I was reading "Black Holes and Time Warps" by Kip Thorne, and right around p.442-443 it talks about how the quantum vacuum fluctuations that give rise to Hawking radiation from an infalling frame of reference give rise to an "atmosphere" of real, non-virtual particles in an accelerated frame...
  37. Hijaz Aslam

    Relative velocity of accelerating and non accelerating particles

    Q. Two particles start simultaneously from the same point and move along two straight lines, one (particle A) with uniform velocity v and other (particle B) with a uniform acceleration a. If ##\alpha## is the angle between the lines of motion of two particles then the least value of relative...
  38. Abishek

    Dual Nature of Photon (and such particles) - WHY?

    I know that photons and other particles of comparatively smaller dimension show dual nature. But why? Can someone help me? :confused:
  39. Fantini

    MHB Particles rotating about each other with uniform angular speed

    Here's the problem: Two particles of mass $m$ and $M$ undergo uniform circular motion about each other at a separation $R$ under the influence of an attractive force $F$. The angular velocity is $\omega$ radians per second. Show that $$R = \frac{F}{\omega^2} \left( \frac{1}{m} + \frac{1}{M}...
  40. K

    Forces between particles at a distance. Can someone please check this?

    Homework Statement How does the electric force between two hydrogen nuclei placed a certain distance apart compare with the force between two helium nuclei placed twice as far apart?Homework Equations F= k * q1 x q2 / d^2The Attempt at a Solution The force would actually be the same between...
  41. ellipsis

    Is distance between particles relative? Poincare invariance?

    If you shift the universe five meters to the left, there is no observational change. If you rotate the entire universe, the inertial frame is also rotated, and there is no observable change. If you freeze time in the universe for one billion years, then resume it, there is no observable...
  42. K

    Force between two charged particles at a distance question, help please?

    Homework Statement Two small electrically charged objects are placed 6 centimeters (cm) apart, where they exert a force of 8 N on each other. How far apart must they be placed in order to exert a force of 1 N on each other? Assuming that the charges on the two objects are equal, what is the...
  43. M

    Partition Functions for FermiDirac and BoseEinstein particles

    Homework Statement Consider two particles, each can be in one of three quantum states, 0, e and 3e, and are at temperature T. Find the partition function if they obey Fermi Dirac and Bose Einstein statistics. Homework EquationsThe Attempt at a Solution I have obtained solutions to both : FD...
  44. P_Ravensorow

    How Do Our Brain Cells Know What to Do?

    I don't know if my question is stupid or something, but I'm going to ask anyway..Say, I am about to sit in a chair or I am about to drink some coffee and keeping in mind that everything is made of electrons, protons and neutrons, how does MY collective particles (Those electrons and protons that...
  45. J

    What if photons were not particles at all?

    I was always thought that photons were electromagnetic wave-particles. What if they were only EM waves and not particles at all. You are probably going to ask. What about polarization? And if there were 2 spaces intertwined at 90 degree angle. You probably have played with polarized glass and...
  46. BUI TUAN KHAI

    Leo's book [energy loss of heavy charged particles]

    Dear all, I am reading the "Techniques for Nuclear and Particle Physics Experiments" of W.R.Leo. I am confused when reading the section 2.2. Energy Loss of Heavy Charged Particles in Atomic Collisions (page 21). At the beginning of the second paragraph (from the bottom up), it is written that...
  47. SalfordPhysics

    Quantum State diagram for system of particles

    Question: "Write the quantum state for the following system of particles distributed over evenly spaced energy levels" The diagram (couldn't upload so hope its not too rough): 5 ---------------------- 4 ---------------------- 3 --------------X------- 2 ------X---X------X---- 1...
  48. O

    Finding Atomic Mass Unit by Subatomic Particles

    If one atomic mass unit is 1/12 of a C-12 atom, so 1 amu must be; 1 Amu = 1/2 ( Mass of proton + Mass of neutron + Mass of electron ) But the equation gives the answers that 1 amu is 1,6737 10^(-27) kg, which is different than the internet says I am using very sensitive values for the...
  49. arivero

    LaTeX Latex Plot of Standard Model: Small and Major Seesaws | Koide Slides

    As a byproduct of the last slides on Koide, I have done a semilogx plot of the standard model in latex with the tikz and pfgplots packages, and it can be generically useful to everyone. So here is the gist: https://gist.github.com/arivero/e74ad3848290845de5ca I call this picture the "small...
  50. H

    Internal Forces in System of Particles

    I am following along with Goldstien's Classical Mechanics Book and I am on page 11. The text is breaking down the total potential energy of a system into two parts: the external conservative forces and the internal conservative forces. My question pertains to the internal forces. Writing the...
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