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. Mayhem

    Particle in a box: Finding <T> of an electron given a wave function

    If ##\hat{T} = -\frac{\hbar}{2m}\frac{\mathrm{d^2} }{\mathrm{d} x^2}##, then the expectation value of the kinetic energy should be given as: $$\begin{align*} \left \langle T \right \rangle &= \int_{0}^{L} \sqrt{\frac{2}{L}} \sin{\left(\frac{\pi x}{L}\right)}...
  2. Gustav

    Electrodynamics: charge of a particle

    I tried solving the problem using the force formula, so what I have known is the magnetic field B and E. I also have a motion in the x-axis, that means that the velocity will be pointed at the x-axis. Inserting this in the formula I will be having something like this: $$\mathbf{F} = q(\mathbf{E}...
  3. Father_Ing

    Torque formula derivation for a particle moving in circular

    Consider that the particle is moving in circular with tangential velocity v, and (0,0)is its origin. I wonder why dr/dt is equal to tangential velocity instead of radial velocity (since dr/dt means how much change in radial distance in a really short duration of time)
  4. I

    Need a force-like unit for classical particle system simulation

    I am doing a learning project by writing a simulation that includes capacitance and current flow amongst capacitors that may potentially be in parallel. I don't care about certain details yet - dissipation factor, frequency dependent effects, temperature. Tiny capacitences within diode junctions...
  5. TheHeraclitus

    Particle ontology and quantum fluctuations

    I have been reading about ontologies in quantum physics recently and I came across Bohmian mechanics. If I understood it correctly BM endorses Particle ontology. Particle ontology claims that point-like particles that move continuously in time are the fundamental building blocks. I know some...
  6. B

    Calculating particle numbers in diffusive equilibrium of a battery

    So I think I have the principles mixed up here because I'm getting kind of "circular" answers. ## N = N_1 + N_2## ##dN## = 0 bc/ particle number fixed so ##dN_1 = -dN_2## ##F = cN^2 = c(N_1 + N_2)^2## In diffusive equilibrium, free energy would be minimized and chemical potentials equal... $$...
  7. orochi

    Courses Learning Parallel Computation as a particle physicist

    I am starting my Master's Degree in Nuclear and Particle Physics, should i invest in taking a course in Parallel Computation? I know the role that Parallel Computation has in particle physics, but is there any use in a particle physicst learning about parallel computation, or could it be...
  8. edusmartin

    B Cloud Chambers - I to know what particle this is

    Hi, my son is fan of the Quantum Physics and we developed a cloud chamber. I'm attaching an image of particle sequence and I will like to find some help to know witch particle is. I will appreciate any help on it. Thanks
  9. physics1999

    I Particle and wave model understanding -- help please

    How does the photoelectric effect prove the wave-particle wrong? Higher intensity does not mean higher energy. If we were to assume the wave-particle model, an increase in intensity means an increase in the amplitude of the wave right? The energy of light is never dependent on amplitude, it is...
  10. L

    Speed of particle after decaying

    I have attempted a solution using conservation of momentum. Could people help check if this solution is correct (the result looks weird), as the problem doesn't have solution with it. $$ \begin{aligned} \begin{pmatrix}Mc \\ 0\end{pmatrix} &= \begin{pmatrix}E_R/c \\ \mathbf{p}_R\end{pmatrix} +...
  11. Amaterasu21

    B Charged Particle on Earth's Surface: Will It Emit Radiation?

    General relativity tells us that an object in free-fall is actually inertial, following a geodesic through curved spacetime, and not accelerating. Instead, it's objects like us, on the surface of a large body, that are accelerating upwards. Maxwell's equations also tell us that accelerated...
  12. U

    A transverse wave traveling through a medium versus a particle of the medium

    I imagine a particle traveling across 1 wave cycle. The total vertical distance traveled across the wave cycle is 4 x the amplitude of the wave. The total vertical distance traveled in 1 minute: 5 cycles in 1 second, thus 5x60 cycles in a minute then 4 x amplitudes effectively traveled per...
  13. O

    I Maximum acceleration of an alpha particle?

    I would like to estimate the maximum acceleration (or deceleration) of an alpha particle that is backscattered by a heavy atom, like in Rutherford backscattering. I am interested in the order of magnitude, not in a precise value. I am assuming the collision is elastic. The kinetic energy of the...
  14. S

    I Why does particle physics predict cosmo constant is 10^120 too big?

    I was reading this article at Wikipedia that says particle physics predicts that the cosmological constant is 10^120 larger than per observation: https://en.wikipedia.org/wiki/Anthropic_principle
  15. jackiepollock

    I Exploring the Advantages of Using Momentum Over Velocity in Particle Physics

  16. crudux_cruo

    B Torque applied by a continuous mass instead of point particle

    I came across this 'problem' when I was trying to think about how a torsion spring would apply torque in something like a miniature catapult. I understand that in the context of something like turning a wrench, we can find the net torque on the wrench by treating the hand applying the force as...
  17. F

    Kinetic and potential energy of a particle attracted by charged sphere

    Hello, I have a particle at point A with charge ##q_A##, and an unmovable sphere of radius ##R_B## at point B with a volumic charge density ##\rho##. The distance from particle A to the centre of the sphere in B is ##r##. Both objects have opposed charges, so, the particle in A, initially at...
  18. F

    Time evolution of a particle in momentum space

    Since it asks for the time evolution of the wavefunction in the momentum space, I write : ##\tilde{\Psi}(k,t) = < p|U(t,t_{0})|\Psi> = < U^\dagger(t,t_{0})p|\Psi>## Since ##U(t,t_{0})^\dagger = e^{\frac{i}{\hbar}\frac{\hat{p^2}t}{2m}}##, the above equation becomes ##\tilde{\Psi}(k,t) =...
  19. ergospherical

    A Massless Particle Action under Conformal Killing Vector Transformation

    For a massless particle let\begin{align*} S[x,e] = \dfrac{1}{2} \int d\lambda e^{-1} \dot{x}^{\mu} \dot{x}^{\nu} g_{\mu \nu}(x) \end{align*}Let ##\xi## be a conformal Killing vector of ##ds^2##, then under a transformation ##x^{\mu} \rightarrow x^{\mu} + \alpha \xi^{\mu}## and ##e \rightarrow e...
  20. J

    A Feynman diagram for bound particle output

    I am interested on how Feynman diagram is formed from a differential equation model of particle interaction wherein the incoming particles are not bound (e.g., separated neutron, proton and electron) and one or more of the outgoing particles are bound (e.g., hydrogen atom). However, I had never...
  21. R

    Potential energy of a particle

    Knowing that ##F(x)=-\mathrm{d}V(x)/\mathrm{d}x##, I found that ##F(x)=-2.4x^3+1.35x^2+8x-3##. But it was the only thing I could find. How can I analyze what will be the type of movement with the information presented by the question statement?
  22. J

    I Particle and Event Horizons in the ΛCDM Model

    According to Wikipedia, The particle horizon is the maximum distance from which light from particles could have traveled to the observer in the age of the universe. It represents the boundary between the observable and the unobservable regions of the universe, so its distance at the present...
  23. debesta

    Job Skills Nuclear physics vs particle physics job prospects

    Which experimental physics branch has better job prospects (both inside and outside academia) - particle physics or nuclear physics? Is the difference very big?
  24. R

    I Probability of finding a particle outside its light cone

    Say we just created a particle (high probability of one-particle state), is the probability of a very far away detector getting triggered at the time of creation (probability of finding a particle outside of its light cone) zero according to QFT? Since we can detect particles and make...
  25. rpthomps

    I Are the daughter particles Ionized when the parent particle beta decays?

    I was wondering if the resulting daughter element is ionized after the parent undergoes beta(or any other kind) of radioactive decay,
  26. PandaKitten

    Estimating the energy of an alpha particle using Bethe's formula

    The question is below. I tried reasoning that because x is constant, E is also constant however that gives me values in the range of 10^51. Then I tried to use numpy's ivp_solve function to solve the differential equation however I wasn't able to get that working either. Apparently I'm meant to...
  27. V

    Would particle P be under non-unform circular motion?

    At t= 0, we can see that the particle P has a radial acceleration of ##-2\hat j## and a tangential acceleration of ##2 \hat i##. The radial acceleration will tend to move it in a circle of a certain radius, whereas the tangential acceleration will tend to displace it parallel to x- axis...
  28. zhangnous

    Hamiltonian for a charged particle in a magnetic field

    I find a exercise in Leonard Susskind's book Classical Mechanics the Hamiltonian of a charged particle in a magnetic field(ignore the electric field) is $$H=\sum_{i} \left\{ \frac{1}{2m} \left[ p_{i}-\frac{e}{c}A_{i}(x) \right]\left[ p_{i}-\frac{e}{c}A_{i}(x) \right]...
  29. M

    I Particle behavior in Penning trap

    Hello! In most of the modern mass measurements in a penning trap, they cool down the degrees of freedom of the ion (the 3 eigenmotions) using resistive cooling, in which they couple an external circuit to some of the electrodes of the trap and the ion is cooled down to the temperature of the...
  30. V

    How to get gravitational force on a gaseous particle?

    This question is very confusing since I don't see two distinct particles that are exerting a gravitational force on each other. Also to complicate matters, a gas is made of many individual particles and I don't know how to determine the gravitational force on a single particle from so many other...
  31. PiEpsilon

    Elastic collision of particle and rotating disc

    Consider the system of the mass and uniform disc. Since no external forces act on the system, the angular momentum will be conserved. For elastic collision, the kinetic energy of the system stays constant.Measuring angular momentum from the hinge: ##\vec L_i = Rmv_0 \space\hat i + I \omega_0...
  32. BWV

    I Diminishing returns from particle accelerators

    Curious about this (https://en.wikipedia.org/wiki/Particle_accelerator) which indicates diminishing returns on new particle accelerators. However to uncover new physics, presumably you need to keep increasing the Lorentz factor by the roughly 10x trend here: So is this hopeless?
  33. simplemind

    I Question about particle interactions and the forces between them

    I have read that if the exchangeparticle of an interaction has even spin then the force between them is attractive if the charge is equal (gravitation) and repulsive if the charge is not equal. Is this wright?
  34. S

    MHB Forces of 8N: Find Angle & Mass of Particle

    Two forces each of size 8N, have a resultant of 13N. a) Find the angle between the forces b) The two given forces of magnitude 8N act on a particle of mass m kg, which remains at rest on a horizontal surface with no friction. The normal contact force between the surface and the particle has...
  35. Krokodrile

    Rectilineal movement of particle

    I tried to resolve this problem with youtube tutorials help, but, i have a many wrong results. The teacher says that the problem requires critics points, so i know that for that points i need a second grade ecuation, but i don't know how interpreter that points. My results: PD: I don't know how...
  36. E

    Probability a particle is in a certain region

    I think I made an error somewhere. In ##[0,a]## I let ##\varphi(x) = \varphi_1(x) := p\sin{kx}## whilst in ##(\xi, \infty)## I let ##\varphi(x) = \varphi_2 (x) := re^{-\gamma x}##, and the constraints at ##x=\xi## are \begin{align*} \varphi_1'(\xi) = \varphi_2'(\xi) &\implies pk\cos{k\xi} =...
  37. E

    A Conservation of energy for stationary particle attached to string

    I was going to put this in the homework forums, but on second thoughts it's more conceptual so perhaps here is better. It's about problem 4, chapter 6 of Wald. Part (a) is fine, $$u^a \nabla_a u^b = \frac{\xi^a}{(-\xi^c \xi_c)^{1/2}} \left( \frac{\nabla_a \xi^b}{(-\xi^c \xi_c)^{1/2}} +...
  38. V

    Forces on particle in complex motion relative to ground observer

    A table with smooth horizontal surface is fixed in a cabin that rotates with a uniform angular velocity ω in a circular path of radius R. A smooth horizontal groove AB of length L(<<R) is made on the surface of the table. The groove makes an angle θ with the radius OA of the circle in which the...
  39. C

    Particle falling radially into a black hole

    I've been stuck starting anywhere with this. I need to finish this class for graduation and i'd like a safety net of a passing grade with this.
  40. JD_PM

    High Energy Books on the Standard Model of elementary particle physics & beyond

    Hello! I am taking a course on Electroweak & Strong Interactions (you could equally call it Standard Model I) and I find it absolutely fascinating! 😍 We studied how weak interactions violate parity, introduction to QCD, flavor physics (CKM matrix, CP violation, …) and neutrino physics...
  41. Twigg

    A What determines particle size in an atomizing spray nozzle?

    Hi all Another random, kinda open-ended question here. Sorry for that. I found myself reading about atomizing nozzles in oil burners, and got curious about the physics of atomized sprays. I didn't have much luck researching this on my own, so I'm turning to you all. It was the kind of situation...
  42. H

    Motion of a particle in a magnetic field

    Hi, I have to find the motion of a particles ##(x,y,z)##. However, I'm not sure where to begin. Is it correct to split the problem and first find what's the motion in the x direction then y and z. For exemple, ##m \frac{d^2x}{dt^2} = -kv_{0x} + qv_{0x}B sin 90 ## ##m\int\int...
  43. Arman777

    Find Height of Particle on a Hoop

    There is a particle with mass $m$ sliding from the hoop with radius R. Its asked to find the height of the hoop which the particles falls. Now I did the hard part (I guess) and find the Lagrangian of the system. Which is given as $$-mR\dot{\theta}^2 + mg\sin\theta = \lambda$$ and...
  44. naviakam

    I Estimating Particle Number in an Electric Field

    In an electric field ##E## if the energy of charged particle (ion) is formulated as ##W=qEr## where ##r## is the distance, how the number of particles is estimated?
  45. DaveC426913

    B Article: "Monster" antimatter particle "slams" into Antarctica

    "A single neutrino has a mass of about 2 billion-billion-billion-billionths of a gram ... A neutrino with 6.3 petaelectronvolts (PeV) of energy ... is equivalent to the energy of a swarm of 6,300 mosquitos [moving at 1mph] ... [or one mosquito accelerated to] Mach-8.2..."...
  46. shankk

    I Issue with wavenumber in the free particle wavefunction

    To me, the ##K## obtained by solving the Schrodinger equation and the de broglie wavelength seem two completely unrelated quantities. Can someone explain why have we equated ##K## and ##\frac{2\pi}{\lambda}##. Also, isn't writing ##p = \hbar K## implying that eigenstate of energy is also an...
  47. J

    I Does the Dilaton field change particle mass?

    The low-energy effective action of the bosonic string is given by: $$S=\frac{1}{2k_0^2}\int d^{26}X\sqrt{-G}e^{-2\Phi}\Big(\mathcal{R}-\frac{1}{12}H_{\mu\nu\lambda}H^{\mu\nu\lambda}+4\partial_\mu\Phi\partial^\mu\Phi\Big)$$ where ##H_{\mu\nu\lambda}=\partial_\mu B_{\nu\lambda}+\partial_\nu...
  48. 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...
  49. 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...
  50. 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?
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