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. docnet

    Find the wave function of a particle in a spherical cavity

    (a) Let the center of the concentric spheres be the origin at ##r=0##, where r is the radius defined in spherical coordinates. The potential is given by the piece-wise function $$V(r)=\infty, r<a$$ $$V(r)=0, a<r<R$$ $$V(r)=\infty, r<a$$ (b) we solve the Schrodinger equation and obtain...
  2. docnet

    Proton in a 1D Box: Energy, Probability, Speed

    a proton is confined to an infinite potential well of width ##a=8fm##. The proton is in the state $$\psi(x,0)=\sqrt{\frac{4}{56}}sin\Big(\frac{\pi x}{8}\Big)+\sqrt{\frac{2}{56}}sin\Big(\frac{2\pi x}{8}\Big)+\sqrt{\frac{8}{56}}sin\Big(\frac{3\pi x}{8}\Big)$$ (a) What are the values of energy...
  3. Kaguro

    Degrees of freedom with a particle and a rod

    The rod itself should have 3 translational+2 rotational DOF. The particle on top of the rod has one additional DOF. So total should be 6. But answer given is 4. What I'm thinking wrong?
  4. K

    Charged particle oscillation about the origin

    Hello! This is probably something simple but I am getting confused about it. Assume we have an electric field along the z axis given by ##E = -kz##, with ##k>0##, so the field on both sides of the xy-plane points towards the origin. Let's say that we have a positively charged ion at the origin...
  5. L

    I Books about Particle Physics and some clarifications

    Hi hi, I would like clarify this, I'm looking for models that can support to a particles have several properties, I know classic physics, my main problem, if we have a fluid with movement forces and heat, the classic model don't support this, only independent from each other... So, a lot of ppl...
  6. T

    Change in the direction of motion of the particle

    Unfortunately, I have no idea about a possible solution.
  7. Y

    Physical Valentine's Day -- quotes from particle physics magazine

    Here are the quotes https://www.symmetrymagazine.org/article/show-your-affection-with-physics-valentines , I find them funny except for the last one is hurtful, I shouldn't say such a thing for someone on a valentine's day because they would care about the valentine's day, personally I find it...
  8. docnet

    A particle in an infinite well

    (a) I guess I should find ##C_n## by normalizing ##\psi_n##. $$∫_{∞}^∞|C_nψn(x)|^2 dx=C_n^2 \frac{2}{a}∫_0^a sin^2(\frac{πnx}{a})dx=1$$ $$C_n^2 \frac{2}{a}[\frac{a}{2}−\frac{a}{4πn}sin(\frac{2πna}{a})]=1⇒C_n=1$$ (b) $$Hψ_n(x)=\frac{-ħ^2}{2m}\frac{\partial^2}{\partial...
  9. V

    Circular motion of a particle around a track -- what provides the centripital acceleration?

    Suppose a particle is moving around a circular track of radius R at speed v. To bend around a circle some agency has to exert an acceleration towards the center of the circle. I analyze the forces acting on the particle, its weight and the normal force and there is no acceleration in the...
  10. R

    Particle constrained on a curve

    I tried 1. using the Lagrangian method: From ##y=-kx^2## I got ##\dot y = -2kx \dot x## and ##\ddot y = -2k \dot x^2 - 2 kx \dot x##. (Can I use ##\dot y = g## here due to gravity?) This gives for kinetic energy: $$T = \frac{1}{2} mv^2 = \frac{1}{2} m (\dot x^2 + \dot y^2) = \frac{1}{2} m (\dot...
  11. R

    I Video lectures in Nuclear and Particle physics? (Undergraduate)

    Hi everyone, I was hoping the internet would be filled with video lectures since lots of universities have been forced to conduct online teaching. However, that doesn't seem to be the case. Therefore I was hoping that some of you know of some great video lectures for nuclear and particle...
  12. I

    Construction How Can I Build a Homemade Particle Accelerator?

    I have very little knowledge on engineering or electrical engineering at the moment, which is why I would like to learn more about it. I have read many articles on them but I am still unclear of some of the materials required for something like this. I am very unqualified to be discussing...
  13. P

    I 100 boxes of Length L, an application of the famous Particle in A Box

    Suppose I have 100 identical boxes of length L and the coordinates are x=0 at one end of the box and x=L at the other end, for each of them. Each has a particle of mass m. V=0 in [0,L], while it's equal to infinity in the rest of the regions. If I make a measurement on position of the particle...
  14. E

    Kinematics: Analyzing circular motion of a particle

    Help please
  15. H

    Oscillation of a particle on a parabolic surface [equation of motion]

    Hi, I have a particle on a parabolic surface $$y = Ax^2$$ and I have to show that the frequency is $$\omega = \sqrt{2Ag}$$ I don't know how to deal with a parabola. I don't think I can use the polar coordinates like a circle. I don't see how to start this problem and in which coordinates...
  16. ChrisVer

    A What is the problem with the particle masses in the Standard Model?

    Hi, Several times I encounter the argument that there is a "problem" with the masses in the Standard Model that we try to "understand". From the one side, you have people who ask why the neutrino masses are so small, and from the other side they ask why the top quark mass is so large. The...
  17. QuarkDecay

    Magnetic Mirror and particle trap

    Suppose we have two charged particles A and B released in the center of the Mirror (where the field is minimum). If A's velocity direction is parallel with the Magnetic field of the mirror and B's velocity is perpendicular with the field, then which one is going to get trapped, or escape, or...
  18. N

    Displacement and distance when particle is moving in curved trajectory

    While solving question 1.13(see the attachment) from Irodov, I was doing this: $$\int_{0}^{\tau}(\vec{v}-ucos\theta) dt=l$$, and $$\int_{0}^{\tau}\vec{v}cos\theta dt=u\tau$$. Solving this gave the answer. However, while solving these 2 equations, I only used the magnitude of ##\vec{v}##, and...
  19. mjmnr3

    Partition function of a particle with two harmonic oscillators

    Here is the solution I have been given: But I really don't understand this solution. Why can I just add these two exponential factors (adding two individual partition...
  20. sergiokapone

    Law of motion for orbiting particle in a uniform magnetic field.

    Hi all, I interested in how can I get low of motion in for orbiting particle in a uniform magnetic field $$\frac{d\vec{r}}{dt} = \vec{\omega}\times\vec{r},\qquad \vec{\omega} = \frac{e\vec{B}}{mc},$$ Of course, rotating about z' axis is very simple. \begin{equation}\label{eq:K}...
  21. namo99

    A charged particle entering a magnetic field -- find the position

  22. Byron Forbes

    Particle analysis of diffraction

    I have done a bit of googling but cannot find anything in this regard at all. It seems to all be "thought of" (rather than explained) by the Huygens–Fresnel principle and other spin offs. Can anyone point me to a particle explanation of diffraction for sound waves? Or does anyone here have...
  23. J

    Fundamental Forces: Force of one charged particle on another

    So first I did the vector stuff. r2-r1= 1.3 i hat-47.5 j hat-14.5 k hat magnitude = 49.68 magnitude squared = 2468.19 Now plugging it all in... F=9E9*6.3E-3*2.8E-3/2468.19=64.322 y vector, -47.5/49.68=-0.956119 j hat Multiply this by force and I get -61.499 but answer should be -36.14
  24. D

    B Particle annihilation -- Is it instantaneous?

    During particle annhilation the rest mass of the particle pair gets converted into momentum with zero time component ie. light. As the pair is colliding do their rest masses decrease and get converted to momentum as a function of distance? Or do they instantaneous annihilate in a discrete interval?
  25. J

    Water analogy in Particle Physics

    There is something unusual about water. Without atmosphere, water can't exist. It's as if water is part of atmosphere. In vacuum, liquid water can't exist. What other things like water where it needs other aspects like atmosphere to exist? And what is the analogy of water in particle physics...
  26. L

    I Charged Particle Free Fall in Grav Field: Does Anyone Know Answer?

    From one point of view the charged particle is accelerating and should emit electromagnetic waves. But from the equivalence principle, I think, it should not. Does anybody know the answer?
  27. Peter Jones

    The oscillation of a particle in a special potential field

    I couldn't prove the first one but i tried to find the period F = -dU / dx = - d( U0tan^2( x / a ) ) / dx = - U0 ( ( 2 sec^2( x / a ) tan( x / a ) / a ) with F=d^2x/dt^2, tan(x/a)=x/a we have d^2x/dt^2 + U0 ( ( 2 sec^2( x / a ) ( x / a^2 ) =0 from there i don't know how to handle the...
  28. Justin_Lahey

    Particle in equilibrium (balancing forces on an object on an incline)

    Hi, I’m wondering if someone can help me understand this question. I can find a resultant force/vector when given an initial angle but I’m stuck here when the only information is the two magnitudes. I think I’m solving for the unknowns but a little lost on how or what equation I should be using...
  29. F

    I Heaviest particle detected so far

    I'm reading this article on Dark Matter and at some point the authors say '' if the LKP [Lightest Kalusa-Klein Particle] is to account for the observed quantity of dark matter, its mass [...] should lie in the range of 400 to 1200 GeV, well above any current experimental constraint.'' My...
  30. greg_rack

    Circular trajectory traveled by a charged particle in a magnetic field

    The Lorentz's force acting on a charged particle perpendicularly "hitting" a magnetic field will be directed upwards, and generally directed towards the center of the circumference traveled by this particle, and so will cause a centripetal acceleration to keep it in a circular motion. By...
  31. C

    Rutherford Scattering of an Alpha Particle

    I have the equation but I am unsure of what my r min would be. Is it the sum of the radii or the difference? I am also confused on what z1 would be. I am fairly sure z2 is the atomic number of Fe(26) but I am unsure of this as well. Edit: I just read that z1 could be 2, is this correct?
  32. T

    Quantum Mechanics determining the normalized constant of a particle

    In my book it has the following example, A particle confined to the surface of a sphere is in the state $$\Psi(\theta, \phi)= \Bigg\{^{N(\frac{\pi^2}{4}-\theta^2), \ 0 < \theta < \frac{\pi}{2}}_{0, \ \frac{\pi}{2} < \theta < \pi}$$ and they determined the normalization constant for ##N##...
  33. Chris Miller

    B Particle Horizon & Coformal Time Near c - Observer Effects

    How would an observer's particle horizon and coformal time be affected by her traveling at very near c (relative to the CMB), both in and opposite the direction of travel (ahead and behind)? Also, how would Hubble expansion be impacted in her frame of reference? (I apologize in advance for...
  34. greg_rack

    Distance traveled by a particle in a transverse wave

    Taken into account the transverse nature of the wave, I deduce the particle must move of harmonic motion from maximum amplitude ##A## to negative maximum amplitude ##-A##. The period ##T=\frac{1}{f}## is equal to the time in which a particle travels a distance ##d=3\cdot A##. I then approximated...
  35. P

    Particle in a box : Schrodinger Eq

    Hi, I'm trying to prove a wave equation of particle in a box situation. In many solutions, they used a equation like Eq = Asin(kx)+Bcos(kx). Instead, I want to prove using Eq = Aexp(ikx) + Bexp(-ikx). So, this is my solution. However, the original (well-known) solution is without i. (psi =...
  36. Adams2020

    A Higgs particle and non-zero expected value in vacuum

    What does the phrase “Due to Lorentz invariance, only the Higgs particle can have a non-zero expected value in a vacuum” mean?
  37. Z

    Energy of a particle in an Infinite square well?

    Here are the results from the python code: Odd results: Even results: I tried to solve for energy using the equation: I substituted the value for a as 4, as in the code the limit goes from -a to a, rather then 0 to a, and hence in the code a = 2, but for the equation it would equal to 4...
  38. L

    Quantum double slits moving past a quantum particle?

    Open question: Can we be sure that a quantum model double slit doesn't create a carrier interference pattern around the slits, in the fields, already there? Relativity is such a big deal in physics but so many models only consider seemingly weird quantum particles going through normal classical...
  39. Boltzman Oscillation

    I Particle Perspective: How Relativity Affects Us

    Some background, I am an undergraduate electrical engineering student with a knack for physics. I plan to attend graduate school for physics but for the meanwhile I've only taken an undergraduate course in QM mechanics, which used griffith's book, and a modern physics course, which covered some...
  40. greg_rack

    Isotope decay via alpha and beta particle emissions

    This problem really confused me, since I can't get the link between particles emitted(alpha and beta, but which are the differences between those?) and changes in mass and atomic number of the isotope. For this one, I can't really show you my attempt since there ain't one...
  41. R

    Electrical Engineer in love with Physics

    I think Physics should not be weird, there have to be explanations or it might mean we don't understand enough.
  42. Zack K

    Spin probability of a particle state

    Starting with finding the probability of getting one of the states will make finding the other trivial, as the sum of their probabilities would be 1. Some confusion came because I never represented the states ##|\pm \textbf{z}\rangle## as a superposition of other states, but I guess you would...
  43. A

    EM radiation temperature vs particle temperature

    I just realized I'm having a problem in understanding this. So let's take an example the CMB is around 160 Ghz and the blackbody temperature within this frequency range is 2.7K which is rather cold as it is close to absolute zero. Then let's take another example, Iter plasma will achieve about...
  44. peguerosdc

    In 2 consecutive decays, determine max and min energies for a particle

    Hi! Instead of just describing my procedure and all my derivations, I really just want to ask if my approach makes sense (actually I have 2 options) to calculate the maximum energy. I am considering c=1 and the problem suggests to consider the neutrino massless: For the first decay, ##Z...
  45. A

    Charge on a particle above a seemingly infinite charge plane

    At first I take the uniformly distributed charge and then divide it by the area of the carpet to get the surface charge density σ -10E-6 C / 8m^2 = σ = -1.25E-6C/m^2 Then I divide the surface charge density by 2e0 to get the electric field strength caused by the infinite plane...
  46. C

    What velocity does the particle need to get to point B?

    It was a long time ago I did these kind of problems so I’m a bit rusty. The only thing I can think of is divide it up to two parts one x and one y. In y the acceleration is sin(a)*9.82? Then put that in the equation and solve for t. In x the there is no acceleration so the formula is x=V0*t, I...
  47. peace

    The motion of a charged particle in a magnetic field

    qvB=mv^2/R R=mv/qB= p/qB ! As you can see, the difference between this relation and the relation in question is in 'c'. Maybe my way is wrong. Maybe I should get help from relativity because the speed of light is involved here. Please help. Thankful
  48. B

    I Muon Time Dilation in Accelerating Frames

    Hi In the book, "Why does E= mc2" by Cox and Forshaw, while discussing time dilation, the example of a muon is given. The authors explain that muons when circulated in the 14 m diameter AGS facility at Brookhaven at 99.94% of the speed of light, its lifetime is increased from the value of 2.2...
  49. W

    B Questions about the Curvaton particle

    Can anyone give a layperson guide to what the curvaton is ? There is a description of it in wikipedia. but It is not clear from the article why it was postulated. Is there any independent reasons for thinking this curvaton field exists other that to generate the right type of spectrum for...
  50. Diracobama2181

    Single Particle Expectation of Energy Momentum Tensor

    $$\hat{T}_{\mu v}(x)=e^{i\hat{P}x}\hat{T}_{\mu v}(0)e^{-i\hat{P}x}$$, so $$\bra{\overrightarrow{P'}}\hat{T}_{\mu v}(x)\ket{\overrightarrow{P}}=e^{iP'x}\bra{\overrightarrow{P'}}\hat{T}_{\mu v}(0)\ket{\overrightarrow{P}}e^{-i\hat{P}x}$$ Now, $$\partial^{\mu}\Phi=\int\frac{d^3 k_1}{2\omega_{k_1}...
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