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. M

    Evolution of a particle in a well

    Homework Statement I posted a picture of the question https://imgur.com/a/8byywYL Homework Equations P = $$(<\psi_{n}|\psi_{o}>)^2$$ The Attempt at a Solution I am guessing that I compute(denote by ##\psi_{o}## the ground state of the old well and by ##\psi_{n}## the ground state of the new...
  2. T

    I Charged particle acceleration across a potential

    Hello, I haven't been able to find the answer to this anywhere. When calculating the energy gained by a particle that is accelerated across the gap of two cavities (e.g. Dees in a cyclotron, or charged cylindrical cavities of a linear accelerator), does one need to take into account the size of...
  3. P

    I Velocity of Particle vs Inertial Frame Velocity

    Hello all, This post is in reference to a previous homework post, found here: https://www.physicsforums.com/threads/show-that-f-gamma-3-ma.338744/ That thread is closed to further replies. Probably because it's nearly 10 years old. That thread is about deriving relativistic force from the...
  4. C

    I Is this outline of particle physics right?

    Just a quick query here: Is the outline of particle physics at the link below right? I have found it very helpful in a general way, but I am only just learning this stuff and don't want to be misled. https://physics.info/standard/concept-map.pdf Thanks!
  5. K

    Classical propagator for massive spin 1 particle

    Homework Statement Calculate the classical propagator for a massive spin 1 particle by inverting the equations of motion to the form $$A_\mu=\Pi_{\mu\nu}J_\nu$$ Homework EquationsThe Attempt at a Solution By solving the lagrangian for a massive spin 1 particle one gets $$(\Box +...
  6. N

    Electrostatics from particle laden air

    Is it possible to generate static electricity from air flow containing particles example smoke or dust flow, or does anyone know of experiments such as the kelvin water dropper converted to generate static from air flow ? Thanks
  7. K

    I Checking my understanding about how massive particle states transform

    I'd like to see whether or not I understood correctly how massive particle states will transform under a homogeneous Lorentz transformation, in terms of the standard four-momentum ##k = (0,0,0,M)##. I suppose we can write $$U(\Lambda) \Psi \propto D^{(j)} (W(\Lambda)) \Psi$$ where ##U(\Lambda)##...
  8. K

    Differential equation for the acceleration of an oscillating particle

    Homework Statement acceleration of certain oscillating particle described by a = -x/9 determine the position of this particle when t = 3π/2 if when t=0 x=0 and v=v0 Homework Equations dv/dt=a The Attempt at a Solution frankly I am not sure how to start but i have two ways in my mind(even i...
  9. P

    Most likely location of a particle versus expected value of

    Hello. I'm using Griffiths' introductory textbook on quantum mechanics, which I have just begun, and have arrived at a question on a simple wave function: The answer to the first question I know to be √(3/b). The answer to part e is (2a + b) / 4. My problem is that I don't understand how...
  10. Abhimessi10

    Motion of a charged particle in magnetic field

    Homework Statement A particle of charge -q and mass m enterd magnetic field B at A with speed v1 at an angle alpha and leaves the field at C with v2 at angle beta.Then, a)alpha=beta b)v1=v2 c)particle remains in the field for time t=(2m(pi-alpha))/qB d)All of these Please see image below...
  11. itoero

    B Particle behavior and the Doppler effect

    How does particle physics explain the doppler effect? (including blue/red shift)
  12. jha192001

    Magnetic Field and a Charged Particle -- relative motion question

    Here's a experiment. There is a magnetic field vertically downward and a charged particle is kept inside it. Simple. Does it experience a force? Now if we move a speed of 2m/s relative to the frame of rest charged particle. Then it must experience a force right?(Becuz now its velocity is not...
  13. M

    How to know 'the displacement of a particle is 'negative'?

    Homework Statement If x1 and x2 are the initial and the final position vectors of particle respectively. Then, displacement of the particle is delta x = x2 - x1 But my question is how to know that the displacement is negtivive and its direaction? (could you provide a practical example so that I...
  14. Sophrosyne

    B Creation and annihilation operators in particle physics

    I was recently reading about annihilation and creation operators in particle physics using the model of an harmonic oscillator, and then quantizing it. This is fine. I can understand it. But how does this quantization of the energy of the harmonic oscillator manifest physically? Is it that only...
  15. P

    Finding the quantized energies of a particle

    Homework Statement Okay, so the question I'm trying to solve is to find the quantized energies for a particle in the potential: $$V(x)=V_0 \left ( \frac{b}{x}-\frac{x}{b} \right )^2$$ for some constant b. The Attempt at a Solution I am following along with the derivation of the quantized...
  16. Sushmita

    Ground state energy of 5 identical spin 1/2 particle

    Homework Statement The ground state energy of 5 identical spin 1/2 particles which are subject to a one dimensional simple harkonic oscillator potential of frequency ω is (A) (15/2) ħω (B) (13/2) ħω (C) (1/2) ħω (D) 5ħω Homework Equations Energy of a simple harmonic oscillator potential is En...
  17. MathematicalPhysicist

    I Can a particle transform into its counter anti-particle?

    So is there a proposed theoretical mechanism for transforming a particle into its own anti-particle? ##Electron \leftrightarrow Positron## ##Proton \leftrightarrow anti-Proton##
  18. J

    CNO fusion using particle accelerator?

    The CNO cycle (see https://en.wikipedia.org/wiki/CNO_cycle) is a catalytic fusion reaction that produces energy in stars larger than the sun. It converts four protons into a helium-4 nucleus using a cycle of carbon, nitrogen and oxygen isotopes as catalysts and releases 26.7 MeV of energy mostly...
  19. P

    Courses Is particle physics that important?

    Hey! I will start my third year on the theoretical physics program. I have taken an introduction course in particle physics, just the basics, not much math. (quark and Feynman diagrams the forces and interaction , CRM matrix and cabibbo angle etc. ) Now I'm choosing between relativistic...
  20. Sushmita

    A particle of mass 'm' is initially in a ground state of 1- D Harmonic oscillator potential V(x)....

    Homework Statement [/B] A particle of mass 'm' is initially in a ground state of 1- D Harmonic oscillator potential V(x) = (1/2) kx2 . If the spring constant of the oscillator is suddenly doubled, then the probability of finding the particle in ground state of new potential will be? (A)...
  21. F

    A How can a mixed state particle absorb a "quanta" of energy?

    Imagine a two-state system, e.g., a single nucleus that can be aligned or anti-aligned with an external magnetic field. If that nucleus is in a "mixed state" at time zero, such that it's wavefunction is 50% up and 50% down at time zero, why can that nucleus absorb a "quanta" of radiofrequency...
  22. A

    A Measuring the spin of a moving Dirac spinor particle

    Hello, I would like to ask about the process of measuring the Spin of a Dirac 4-spinor Ψ that is not in the rest frame. Note that even though there is plenty of information about what a Dirac spinor is, what reasoning lead to its discovery and how it can be expressed in terms of particle and...
  23. M

    Other Navigating a Short PhD in Experimental Particle Physics

    Hello! I am not going to give details about the situation (for obvious reasons) but here it is: I got accepted for PhD to a very good American university, in experimental particle physics and I met a famous professor here who is willing to be my mentor. I talked to some of his old students and...
  24. astroman707

    Plot the position of the particle x=Acosbt

    Homework Statement The position of a particle as a function of time is given by x=Acosbt, where A and b are constants. The first question asks to roughly plot the position of the particle over the time interval (0,7) seconds. The second asks what time the particle passes the origin, and what...
  25. AkshayM

    Projectile Motion and acceleration of particle

    Homework Statement If a particle moves in X-Y plane with acceleration non zero in X and Y , the particle will not move in a parabolic path True or False ? Homework Equations X = UxT + 1/2(Ax)T^2 Y= UyT + 1/2 (Ay)T^2The Attempt at a Solution The equation of trajectory that i came up with...
  26. J

    Velocity of a particle at time t in a rotating frame

    Imagine two frames one inertial (x,y,z) and the other rotating (x',y',z'), their origins are always coincident. The rotating frame is rotating as seen from the inertial frame with a time-dependent angular velocity ##\boldsymbol{\Omega}(t)=(\Omega_x(t),\Omega_y(t),\Omega_z(t))##. In the rotating...
  27. D

    Particle physicist/cosmologist

    is there other theoretical physicist that is both particle physicist and cosmologist? i only see randall sry i just need a quick answer.. anyways, ill be skimming all female scientists in wikipedia
  28. J

    A Exceptional Quantum Geometry and Particle Physics

    What do you think about the article Exceptional Quantum Geometry and Particle Physics Posted by John Baez https://golem.ph.utexas.edu/category/2018/08/exceptional_quantum_geometry_a.html and the following discussion? It also includes links to the original papers. Exceptional quantum geometry...
  29. Pushoam

    Momentum measurement of a particle in Quantum Mechanics

    Homework Statement What will momentum measurement of a particle whose wave - function is given by ## \psi = e^{i3x} + 2e^{ix} ## yield? Sketch the probability distribution of finding the particle between x = 0 to x = 2π. Homework Equations The Attempt at a Solution The eigenfunctions of...
  30. Nevada City Bob

    I Bosons: Explaining Particles That Defy Imagination

    I've never been able to get my head around the idea that forces are particles. In the case of fermions, a particle seems to be a natural concept. Even though it's really a wave, or an excitation in a quantum field, I can envision it as being something in a particular place. For bosons that...
  31. Nevada City Bob

    Bob from Nevada City, CA

    Hi. I'm a retired software engineer who has always been fascinated in science. I was a math major in college, before the time that computer science majors were a thing. My key areas of interest these days are particle physics and quantum mechanics. I'll be asking some questions that have...
  32. Pushoam

    I Light : Wave - particle duality

    Interference pattern made by light shows the wave nature of light and photoelectric effect shows particle nature of light. So, what is light? According to the photoelectric effect, light consists of photons with energy E and momentum ## \vec p##. According to the interference pattern, we...
  33. H

    A Calculating Particle Lifetimes to Unstable Particle Decay

    The lifetime of Tritium is about 13 years. The lifetime of positronium is about one-tenth of a nanosecond. Can you point me to some papers or tell me how to calculate the lifetime of an unstable particle? For example, suppose I want to calculate the lifetime of the pion? Or muonium? Etc.
  34. AlvisPrabhu

    How are Photons massless? How can a particle have no Mass?

    I did look it up , but couldn't find anything that explains this in a simple manner.
  35. Spinnor

    B Remaining Fraction of Particle Beam After CERN Use

    When Cern is done with a particle beam, what fraction of a typical beam bunch is left having not scattered out of the bunch? Is it of order 1/2? A very rough estimate would do. Edit, I should add that I read an accelerated beam might be used for a day and at the end of the day they dispose of...
  36. pintu935

    I What does complex potential energy mean for a particle?

    Griffith says in problem 1.15 the potential energy has an imaginary part. my question is that any real case exists where the part of the potential energy is imaginary?
  37. P

    I Particle goes through a double slit + decays, what happens?

    What would happen if you send a particle towards a double slit, it goes through interacting with itself quantumly, however before it reaches the screen it decays emitting radiation (Alpha, beta and/or Gamma)? Would you still see the same pattern on the screen? Would it affect the wave function...
  38. jedishrfu

    B Imaging of Light as a Particle and a Wave

    In this article, researchers have used electrons to image light as both particle and wave at the same time. https://phys.org/news/2015-03-particle.html
  39. Abdul Quader

    I Free particle: Quantum and Classical treatment

    I have a problem finding ##\left|Ψ(x,t)\right|^2## from the following equation: $$Ψ(x,t) = \frac 1 {\pi \sqrt{2a}} \int_{-∞}^{+∞} \frac {\sin(ka)} k e^{i(kx - \frac {ħk^2} {2m} t)} dk$$ and tried to plot like the pic below (Source Introduction to quantum mechanics by David. J. Griffiths, 2nd...
  40. M

    A Relation between the track of a particle and its energy loss

    Hi, I'm trying to simulate the process of charged particles attenuation in matter (like this) by a montecarlo-metropolis algorithm in Python. I thought that I could use for the number of particles at thickness ##x## the formula ## N (x) = N_0 e^{-\mu x} ##, so the probability in this case will...
  41. V

    Find Angular Velocity for Moving Particle Parallel to x-Axis

    Homework Statement A particle is moving parallel to x-axis in the positive direction with velocity v such that at all the instants the y -axis component of its position vector is constant and is equal to 'b'. Find angular velocity about origin. Homework EquationsThe Attempt at a Solution I...
  42. M

    I What causes an elementary particle to "decay"?

    What causes an elementary particle to "decay" into other elementary particles? And where do these particles come from if they were not part of the original particle?
  43. MichaelJT

    How Can an Undergraduate Physics Student Contribute to a Physics Forum?

    Hello! I am a current undergraduate physics student with a keen interest in primarily astronomy and particle physics. Keen to help out some with some basic homework questions and read more about people's experiences in the field of physics!
  44. S

    What is the range and time period of this particle?

    Homework Statement The longer-range inter-nucleon force is not a direct result of the gluon field, but is indirectly affected by a quark-antiquark pair (i.e. meson). If this ‘residual’ strong interaction between nucleons is mediated by a π-meson, then what is the maximum time period in which...
  45. T

    An experiment to determine ceramic particle sizes

    Homework Statement (I) An experiment to determine ceramic particle sizes showed that the rate of descent when suspended in a fluid ranged from 1.2 × 10–6 m s–1 to 5 × 10–6 m s–1. 
The density of the material was 3800 kg m–3 and the density and viscosity of the fluid at room temperature were...
  46. mehdi6

    I Computational particle physics

    Hi to all, I have a random number generator in FORTRAN, which gives a random numbers to my particles initial velocity in three dimension (vx,vy,vz). If, I want to make my particles to embark to move with a specific weight (eg. Maxwellian), what should I do? absv = sqrt(vx*vx+vy*vy+vz*vz) wt=...
  47. cliffhanley203

    Wave / particle duality of light

    Homework Statement I've just read that light can behave like a wave at times, and a particle at other times. How does the light from the Sun traveling towards Earth behave? A wave? A particle? Or both? And is it in any sense something that actually starts at the Sun, travels across space and...
  48. F

    I Heisenberg - Uncertainty principle - lifetime of a particle

    I have seen that the more a particle has a high energy, i.e ##E##, the more its lifetime is short, respecting so the uncertainty principle. But by the definition of this uncertainty principle : ##E\,\Delta t \geq \dfrac{\hbar}{2}##, I can write : ##\Delta t \geq \dfrac{\hbar}{2E}##, then...
  49. T

    B Is the kinetic energy of a particle quantized?

    Is the kinetic energy of a particle quantized? Does it increase and decrease in discreet amounts?
  50. P

    Motion of particle changing forces

    I've got a question and can't find any answer on google. So the centripetal force for a particle in uniform circular motion is mv^2/r. This also means that if F > mv^2/r than the particle will get closer to the center and if F < mv^2/r than it will travel further from the center. Say a 5 kg...
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