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. qnach

    I Is Light a Particle or a Wave in Different Contexts?

    Is "a light, particle or wave" an absolute question or a relative question? Should a light be considered as a particle or as a wave depends upon the relative size of the system? When considering a visible light relative to a basket ball should it be considered as particle, while a visible light...
  2. M

    B Interference pattern, one particle at a time

    [Mentor's note: Split off from another thread because it's a different question] I have a question about the single-photon double-slit experiment's results that isn't about the role of consciousness. Should I go ahead and ask it here or ask it elsewhere? (Briefly: If the results are lots of...
  3. J

    B What is the Fastest Particle Speed at 0°C?

    How fast does the fastest subatomic particle travel at? When left at a temperature or zero degress Celsius.
  4. quantumSpaghetti

    I Rotational excitation of quantum particle

    I was watching a lecture and there was a connection drawn between classical rotational energy and quantum rotational excitation. The energy of a rotating system is $$E = (L^2) / 2 I $$ with L being the angular momentum and I the moment of Inertia. Then to make it quantum$$ n^2 * ħ^2$$ was...
  5. S

    Particle Introductory book on particle physics

    Hello! Can someone please recommend me a particle physics book that starts from the very basic concepts, but gives complete proofs for everything (for example, I want to start with the "spinless" particles interactions as an introduction to Feynman calculus, but I don't want them to just write...
  6. A

    B Need Listing of Photon and Particle Quantum States

    Hi, I am learning quantum entanglement. I am interested to create an up to date list of all known : - Photon Quantum States - Particle Quantum States - Classically entagled photon states I guess that there is an organization out there that already have this info. If someone can point me into...
  7. N

    I Diameter of nanoparticles formed by dewetting of thin film

    Hi, I'm trying to understand the derivation to an equation I found in the following paper: http://pubs.acs.org/doi/abs/10.1021/nn203035x I posted almost this exact question on Physics Stack Exchange but got no replies so I decided to try it here instead, I hope that's ok...
  8. D

    Equation for the motion of an iron particle in a magnetic field

    Hello, Let's assume we put a small iron particle in a magnetic field. What is the equation of the route that the particle performs? Is it the minimal route length that is possible? (the magnet is a stick-form)
  9. G

    Particle Motion (Astrophysics)

    Homework Statement This is new for me, so forgive me my clumsiness. I am working on the following problem: A particle p is moving with a velocity v1 = c (speed of light) towards an object q, which is moving in the same direction with the speed v2, where v1>v2. Now, v2 is a function of the...
  10. F

    I Particle in the box eigenfunctions

    Hello Everyone, For the particle in the 1D box of width ##L##, the time invariant Schrodinger equation is cast in the form of the Hamiltonian operator and automatically leads to the energy eigenfunctions $$\Psi(x) = \sqrt{\frac 2L} sin(n\pi x/L)$$ I know that these energy eigenfunctions...
  11. C

    B Standard model particle properties

    In the Standard Model, for any particle, I have only found properties related to electromagnetic and gravitational (in fact mass does not necessarily mean it is a property related to gravity, but to emergy)forces like charge and mass. Why there isn't anything about the other two interactions...
  12. michael879

    I Understanding Relativistic Ptcl Lagrangian: S1 vs. S2

    Can someone help me understand how the following two actions are related? S_1 = \int \left(-\dfrac{1}{2}mg_{\mu\nu}\dot{x}^\mu\dot{x}^\nu - U\right) d\tau S_2 = \int \left(-m\sqrt{g_{\mu\nu}\dot{x}^\mu\dot{x}^\nu} - U\right) d\tau Both of them lead to the correct geodesic equation as the...
  13. F

    Work done by particle in a box in expanding the box?

    Homework Statement I'm given that the energy of a particle in a rectangular box is the following: E =\frac{\hbar \pi^2}{2m}(\frac{n_x^2}{L_x^2}+\frac{n_y^2}{L_y^2}+\frac{n_z^2}{L_z^2}) I'm to show that if the length of the box is increased adiabatically and quasistatically from L_x to 8L_x...
  14. B

    How can a pi_0 meson decay into 2 photons?

    Homework Statement Earlier my teacher put this equation on the board, π_0 --> γ+γ It appears to work until you consider spin. Homework Equations a quick google search reveals that the spin of a photon is +1 and the spin of a pi meson is 0 The Attempt at a Solution This appears to work for...
  15. E

    Relative Acceleration - Particle and Wedge

    I would be very grateful for help with deriving the following equation... "A smooth fixed plane is inclined at 30 degrees to the horizontal. A wedge of mass M and angle 30 degrees is held on the surface so that its upper face is horizontal, and a particle of mass m rests on this face. The...
  16. S

    Particle in an Electromagnetic Field

    Using the Lagrangian : L = ½mv^2 - qφ + qAv What is the physical intuition of Av ? I know that A is the magnetic vector potential and that v is the velocity of the charged particle. I just don't know what their dot product means physically .
  17. Lola1

    I Spectrum energy of a particle moving on a circumference

    If you consider the one-dimensional case of a particle constrained to move on the edge of a circumference, the energy spectrum is continuous and two times degenerate. Why the fact that the particle can move in clockwise and counterclockwise implies that the spectrum is degenerate twice? In any...
  18. M

    I Accelerate Charged Particle: Does Light Require Force?

    Does a charged particle need to experience a momentum changing force to emit light? Or is it sufficient for an observer to accelerate relative to the particle?
  19. ReidMerrill

    Applying particle in a box boundaries to an eigenfunction

    Homework Statement Use the eigenfunction Ψ(x) =A'eikx + B'e-ikx rather than Ψ(x)=Asinkx + Bcoskx to apply the boundary conditions for the particle in a box. A. How do the boundary conditions restrict the acceptable choices for A’ and B’ and for k? B. Do these two functions give different...
  20. FallenApple

    A photon vs an electron. Wave or particle?

    So we know for a fact that an electron is a particle. The "wave" like properties are not waves at all, its just the wavefunction that is a mathematical wave which is used for getting probabilities for where the electron will end up. But what about a photon? When a charge oscillates, its gives...
  21. Jr_Particle_Hunters

    B Beta particle penetration in our cloud chamber?

    Hello. We are elementary school kids who built a cloud chamber for our science project to test out the effectiveness of different shields against background radiation. We are not sure about something involving beta-particles. Can you help us please? We know low-energy beta particles cannot...
  22. T

    Motion of a particle in eletric field

    Homework Statement Hi guys. Just wondering if anyone could help me with Q7 part a) on the pdf I have attached below. I think my working are not correct but I can't see other way. If I add 6. and 7. together I would get an ans in terms of what the question is asking but I am not sure if that is...
  23. Peter Hessellund

    How quickly do ocean spray droplets dry into solid salt particles?

    When a bubble in the ocean bursts water drops are thrown into the air. How fast do these water drops dry out creating solid salt particles? There must be a formula for calculating this and I am guessing that the following variables must figure in the formula: - Droplet size - Salt concentration...
  24. M

    I Particle distribution as a function of radius in astrophysics

    Hello everyone, I am working on a project in astrophysics in which I need to include now some type of particle distribution (as a function of the radius). I was wondering if there is some accepted function that would describe the number of particles per radius in astrophysics. Saturn's rings...
  25. Guaicai

    What is the relationship between energy and mass in a two-particle collision?

    Homework Statement In a two-particle collision the square of the invariant mass is. M is total mass of the system (M2 is the square of the total mass) m is the mass of each particles E is the energy of each particles p is momentum vector of eache particles Homework Equations M2 = (E1+E2)2 -...
  26. G

    I'm thinking about 2nd Ph.D. for particle physics

    Hello. I'm actually taking Ph.D. course for plasma physics and I think I'll finish this course within this year. I took classes in quantum field theory and general relativity in last semester luckily and experience of these subject ignited a desire to study theoretical particle physics and...
  27. F

    Alpha Particle Approaching a Gold Nucleus

    Homework Statement An alpha-particle with velocity 3.5 x 106 strikes a block of gold, atomic number 79 and mass number 197. Find the distance of the closest possible approach between the alpha particle and a gold nucelus, assuming Coulomb's law holds over such distances. Assume mp = mn = 1.67 x...
  28. Kaura

    Solve for Path of Particle: x - 2cos(arcsin(y/2)) = 0

    Homework Statement Suppose that a particle follows the path r(t) = 2cos(t)i + 2sin(t)j Give an equation (in the form of a formula involving x and y set equal to 0 ) whose whose solutions consist of the path of the particle. Homework Equations None that come to mind The Attempt at a Solution I...
  29. D

    Engineering Career path for particle accelerator engineering?

    I'm currently in year 12 (studying IB with hl physics, maths and chemistry) in the UK and am starting to look at uni courses. For a few years now I have been absolutely fascinated by the particle physics/quantum side of physics. At the movement I would love to work in research in this sort of...
  30. Rabu001

    Courses Particle physics vs engineering (advice is much appreciated)

    Hello there, I have always loved physics and wanted to get a degree in physics, particularly particle physics. But my father told me that if i have a physics degree i won't be able to get a job easily so i should pick an engineering course instead. i looked through engineering types but i...
  31. Pyrus

    I What is the basic concept of the spin of a particle

    What is the basic concept which decides the spin of a particle. Like, electron has a spin of +- 1/2... What do this 1/2 signifies. Other spins are also there like 1 and 2. What do they signify? Is there any possibility of any particle with spin other than 1/2, 1 or 2?
  32. P

    I Reflection of a massive particle

    Is the reflection of a (massive) quantum particle from a mirrored surface considered a Lorentz Boost?? If it is non-collinear ?
  33. ChrisisC

    B Maths used in Quantum physics, specifically particle physics

    What are the main maths used in the mentioned fields of physics? Not just general terms like "Calculus" but more specific maths. Also, what is the logic behind using these to solve problems in physics? Example, why would someone use differential calculus to calculate the probability of a...
  34. A

    Effect of particle size on boiling point in solution

    Hello. Suppose you dissolve something in water. I know that the boiling point should increase because as the water boils the solute's entropy decreases, and the net entropy should increase. Now suppose, that I dissolve GI chlorides in the water. Each solution of the salt has the concentration...
  35. Spinnor

    B Particle of M=0, Q=1, S=1/2, Confined?

    Hypothetically, could we have a mass-less electrically charged particle of spin 1/2 confined by a hypothetical potential so that at large distance scales the particle looked like localized massive charged particle of spin 1/2? I'm thinking of a mass-less charged particle that does some kind of...
  36. M

    Charged Particle in Magnetic field calculation

    Homework Statement Basically having a problem when trying to theoretically calculate the mass of alpha particle in a charged field. r is the unknown radius of curvature m = mass of an alpha particle (6.646 *10^-27 kg) v = velocity of an alpha particle immediatly after decay (1.381 *10^7 m/s)...
  37. K

    Aberration of a Particle: Solving for Angle and Velocity in Relativistic Frames

    Homework Statement A particle has speed u‘ in the S’ frame, its track making an angle ## \theta’ ## with the x’ axis. The particle is viewed by an observer in frame S, the two frames having a relative speed parameter ## \beta ##. (a) Show that the angle ## \theta ## made by the track of the...
  38. FallenApple

    Correct operation for coordinates of hoop particle system?

    Homework Statement All in the pic below. Part of the solution presented. Didn't present the whole thing as that would clutter the page. I just want to know how they set up the x coordinate for the particle. Homework Equations This problem is just about using the lagragian. So my issue is...
  39. O

    Force on a relativistic particle

    Homework Statement [/B] A particle of rest mass ##m_0## is is caused to move along a line in such a way that its postion is $$x = \sqrt{b^2 + c^2 t^2} -b$$What force must be applied to the particle to produce this motion? 2. Homework Equations The velocity of the particle as seen from...
  40. A

    I 'Localization,' particle motion, and quantum fluctuations....

    Hi all, Some time ago I was reading about Anderson localization (posted a question about it was well) - this got me thinking about vacuum fluctuations. I think I have the wrong idea in my mind - so wanted to ask the great community here about it: Quantum (vacuum) fluctuations must have an...
  41. R

    B Directed Energy: Low Intensity Applications

    Mostly used for weapons, can sources of directed energy be contained at low intensities? In theory, could it be set to specific wavelengths, frequencies, intensities or whatever to say remove particles of lower cohesiveness from other surfaces or materials?
  42. ChrisisC

    Physics Particle Physics and Quantum Physics

    I am trying to figure out what winfield oh physics i should study for a career. I absolutely love learning about strange quantum phenomena but also love learning about extremely small particles and how they interact at the smallest of scales Would i be interested in a career in particle physics...
  43. H Psi equal E Psi

    Two particle in a square potential well?

    Hi guys! I'm struggling with the following problem: Consider two distinguishable (not interacting) particles in a quadratic 2 dimensional potential well. So ## V(x,y)=\left\{\begin{matrix} 0,\quad\quad-\frac { L }{ 2 } \le \quad x\quad \le \quad \frac { L }{ 2 } \quad and\quad -\frac { L }{...
  44. J

    A Accelerating particle photon emission mechanics?

    It's been a while. But I have always received the help I needed on this forum. I had this question in my head, When a particle accelerates, it creates an oscillating electric field, and a photon. How much does this effect, affect the energy of the particle itself? Say I had a particle...
  45. adsorption

    I Anyone knows V-Sorb 2800 BET surface area analyzer principle

    we interest one V-Sorb 2800 BET surface area analyzer, using physical adsorption principle to test particles surface area data, if anyone knows this analyzer principle?
  46. M

    A Recent papers on particle masses

    http://arxiv.org/abs/1612.03825 Towards a new paradigm for quark-lepton unification Christopher Smith (Submitted on 12 Dec 2016) My comments: This is my favorite. It is a modification of Minimal Flavor Violation (MFV), a popular philosophy which posits that any BSM couplings may only involve...
  47. E

    Coulomb scattering of spin-zero particle (QFT)

    I'm looking at Aitchison and Hey's QFT book, trying to verify Eq. 8.27 (which is in fact problem 8.2). It asks us to verify that the matrix element for the scattering of a charged spin zero particle (s^+) is <s^+,p'|j^\mu_{em,s}|s^+,p> = e(p+p')^\mu e^{-i(p-p')\cdot x} where...
  48. A

    Gas Collisions in Containers: Comparing Ratios of Wall Collisions"

    Homework Statement You have two samples of the same gas in the same size container, with the same pressure. The gas in the first container has a kelvin temperature four times that of the gas in the other container. The ratio of number of collisions with the wall in the first container compared...
  49. Andrea_G

    Schools Particle Physics PhD: Find a School & Make an Application

    I'm a Nuclear Physics student and I'm finishing the university in this period. I was searching for a PhD in Particle Physics but I don't know where to go, anyone knows some interesting school to make an application? Thanks
  50. N

    B If an imaginary quasiparticle has a mass depending on speed

    ...becoming infinite at rest, doesn't that mean it has infinite mass whatever velocity it has? How could that quasiparticle be at rest to achieve infinite mass?
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