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. Athenian

    [Special Relativity] Test Particle Inside the Sun's Gravitational Field

    Below is an attempted solution based off of another user's work on StackExchange: Source: [https://physics.stackexchange.com/questions/525169/special-relativity-test-particle-inside-the-suns-gravitational-field/525212#525212] To begin with, I will be using the following equation mentioned in...
  2. P

    Particle decaying into two daughter particles - special relativity

    Right, so I thought I'd done this correctly but clearly not because my velocity is greater than the speed of light, where have I gone wrong? P = (M, 0, 0, 0) p1 = (E1, p1x, p1y, p1z) p2 = (E2, p2x, p2y, p2z) P = p1 + p2 p2 = P - p1 square each side to get (p2)2 = P2 - 2Pp1 + p12 therefore (m2)2...
  3. Saptarshi Sarkar

    Energy of particle when under a central force

    I calculated the potential energy of the particle as follows : But I am not sure how to calculate the kinetic energy. I know that if it was a satellite orbiting a Earth, I could use ##\frac {GMm} {r^2} = \frac {mv^2} {r}## to calculate the velocity v and they I could calculate kinetic energy...
  4. karush

    MHB 2.1.2 AP Calculus Exam particle at rest

    ok I chose e for the zeros
  5. C

    I Understanding Atomic Particle 'Spin': Exploring Its Physical Meaning and Value

    I've been looking hard (really, I have) for an explanation of what 'spin' is. Is there any way to explain this in a physical-real way, or is it 'just a thing'? Every description I have come across, and I mean dozens, say something like 'well, it's like angular momentum but it isn't really that...
  6. JD_PM

    Central force on a particle following a logarithmic spiral

    I want to focus this question on understanding the force ##F(r)## I get (thus, I want to focus on c) ). However, below the dashed line, I included steps on how I derived ##F(r)##. We are going to work in polar coordinates. Knowing that the acceleration is: $$a = \Big( \ddot r - r \dot...
  7. A

    B Unraveling the Tachyon and Photon Debate: Exploring Faster-Than-Light Particles

    A tachyon or tachyonic particle is a hypothetical particle that always travels faster than light. Most physicists believe that faster-than-light particles cannot exist because they are not consistent with the known laws of physics. - Tachyon definition The photon is a type of elementary...
  8. FireAP

    Point sized particle collision and no transfer of energy

    Two identical point-sized particles with the same Y-coordinate were traveling along the X and Z axes respectively. Given that gravity is acting parallel to the Y-axis, will the particles when they eventually collide, continue traveling along the same linear path due to work done by either being 0?
  9. karush

    MHB 2.1.2 AP calculus Exan particle move along the x-axis

    A particle moves along the x-axis. The velocity of the particle at time t is $6t - t^2$. What is the total distance traveled by the particle from time $t = 0$ to $t = 3$ ok we are given $v(t)$ so we do not have to derive it from a(t) since the initial $t=0$ we just plug in the $t=3$ into $v(t)$...
  10. B

    I Effective ways of accelerating a 50 picogram particle

    Would it be practical to accelerate a 50 picogram particle to speeds on the order of 1,000,000 meters per second (in a high vacuum environment) using methods typically used in particle accelerators? 2 methods that come to mind are a series arrangement of parallel pate accelerators and a moving...
  11. Saptarshi Sarkar

    A particle of unit mass moves under the action of force F=-k²/x³ ....

    I tried solving the differential equation by integrating both sides wrt t but this does not work out and I am doing something wrong. How do I integrate such an equation properly? d²x/dt² = -k²/x³ => dx/dt = -k²t/x³ => x = -k²t²/2x³ + d
  12. E

    B Why can I only resolve tangentially on a point particle?

    For instance, in the case of a simple pendulum, it is quite acceptable to write down ##-mg\sin{\theta} = ma_{tangential}##, and go from there. However, if we introduce a rotating body which is not a particle, we may still calculate its torque from its centre of mass, however we can no longer...
  13. E

    Closest approach of alpha particle - two separate methods

    I've found two methods for doing this problem and they give different answers. Method 1: Assume the larger nucleus does not move, and simply equate energies before the collision and at the point of closest approach:$$\frac{1}{2} m v^{2} = \frac{qQ}{4\pi\epsilon_{0}r}$$ Method 2: Assume the...
  14. H

    Necessary KE of particles to create a resulting particle in a collision

    So I am making the assumption that the resulting particle Z is emitted at rest. For part a I believe that since the two positron beams are symmetric they would each provide half of the energy to create the Z particle so the KE of each positron would be 91.187GeV/2, I am ignoring the rest energy...
  15. H

    Finding the velocity of an emitted particle from a decay

    So I know that the total energy of the system initially is 775.5MeV, because the meson is at rest. Also by conservation of energy I know that the total final energy of the system is the same thing. I also know that the initial momentum of the system is 0 because the particle is at rest. This...
  16. M

    Find the probability of a particle in the left half of an Infinite Square well

    Attempt: I'm sure I know how to do this the long way using the definition of stationary states(##\psi_n(x)=\sqrt{\frac {2} {a}} ~~ sin(\frac {n\pi x} {a})## and ##\int_0^{{a/2}} {\frac {2} {a}}(1/5)\left[~ \left(2sin(\frac {\pi x} {a})+i~ sin(\frac {3\pi x} {a})\right)\left( 2sin(\frac {\pi x}...
  17. B

    What is the value of the second term in the commutator for an N particle system?

    I have insertet the equations for H and P in the relation for the commutator which gives $$[H,P] = [\sum_{n=1}^N \frac{p_n^2}{2m_n} +\frac{1}{2}\sum_{n,n'}^N V(|x_n-x_n'|),\sum_{n=1}^N p_n] \\ = [\sum_{n=1}^N \frac{p_n^2}{2m_n},\sum_{n=1}^N p_n]+\frac{1}{2}[\sum_{n,n'}^N...
  18. T

    Particle in a well, can someone explain how this step works

    Homework Statement:: A particle with mass m is effected by potential V(x) = ∞ when x<0, -V0 when 0<x<a, 0 when x>a A) Set up a relation from which the energy for bounded states can de determined B) For which values V0 does the particle have only one bounded state? Homework Equations...
  19. L

    I The free particle in spherical coordinates

    Hi! I'm studying Shankar's Principle of quantum mechanics I didn't get the last conclusion, can someone help me understand it, please. Where did the l over rho come from?
  20. Maslova

    B Position of a particle and photons

    Once I have read that we can’t know a actual position of a particle because to see the particle we need to send photons and when we send photons it colides with the particle and change it’s position. Is this true?
  21. M

    Show that the Hamiltonian is Hermitian for a particle in 1D

    I need help with part d of this problem. I believe I completed the rest correctly, but am including them for context (a)Show that the hermitian conjugate of the hermitian conjugate of any operator ##\hat A## is itself, i.e. ##(\hat A^\dagger)^\dagger## (b)Consider an arbitrary operator ##\hat...
  22. W

    I How to derive the currents of Z boson and the EM current?

    I am a student minor in physics and I am taking this course of particle physics. And I have been lost since the Non-Abelian Gauge Theory which a few lectures before Electroweak unified Theory lecture. i am completely confused and overwhelmed by the math since the mid-term exam, since I was not...
  23. D

    I Can Different Shapes of Slits Affect the Diffraction Pattern of Single Photons?

    What I've seen of the experiment involves sending a stream of particles through the slits. I'm extrapolating when I say that the interference pattern could be caused by electromagnetic fields (in the case of massive particles), especially because the particles are moving and probably spinning as...
  24. Boltzman Oscillation

    Solving Schrodinger's Equation for a Particle in an Infinite Box

    Firstly, since there is no condition for the z axis in the definition of the potential can I assume that V(x,y,z) = .5mw^2z^2 when 0<x<a, 0<y<a AND -inf<z<inf? If so then drawing the potential I can see that the particle is trapped within a box with infinite height (if z is the...
  25. G

    Travel time of a particle suspended from an elastic string

    Hi, Can anyone please help me with the following: I have found the velocity of projection, no problem, it is v = 2*sqrt(10) Also, in obtaining this value, I have also found the extension in the string when in equilibrium, it is x = 2 Now on to the time of flight. The given answer is: t =...
  26. zizzle

    Minimum initial speed to spin a particle around a disk (with gravity)

    For this problem, since the weight force on the "particle" (child) is not always aligned with the tangential circular path of the disks, I couldn't think of a way to use rotational kinematics equations. As such, I tried to solve the problem using work principles (namely, that the change in...
  27. karush

    MHB 2.1.314 AP Calculus Exam a particle moves along the x-axis......

    ok again I used an image since there are macros and image I know this is a very common problem in calculus but think most still stumble over it inserted the graph of v(t) and v'(t) and think for v'(t) when the graph is below the x-axis that participle is moving to the left the integral has a...
  28. C

    I Question regarding a Free particle and Hilbert space (QM)

    In quantum mechanics, the Eigenfunction resulting from the Hamiltonian of a free particle in 1D system is $$ \phi = \frac{e^{ikx} }{\sqrt{2\pi} } $$ We know that a function $$ f(x) $$ belongs to Hilbert space if it satisfies $$ \int_{-\infty}^{+\infty} |f(x)|^2 dx < \infty $$ But since the...
  29. bubble-flow

    Oscillation of a particle inside water caused by a sound wave

    I don't really know where to start as this is not exactly my homework and I finished school some 15 years ago. I looked into my old high school notes, the last time I ever had anything about mechanical waves and sound. Unfortunately, we never learned anything about sound waves causing...
  30. sergiokapone

    Equation of motion in polar coordinates for charged particle

    A solution of equations of motion for charged particle in a uniform magnetic field are well known (##r = const##, ## \dot{\phi} = const##). But if I tring to solve this equation using only mathematical background (without physical reasoning) I can't do this due to entaglements of variables...
  31. TechieDork

    B I've heard that particle physics is just like taxonomy and botany

    I've heard it from my classmates that particle physics is just like botany or when physics meets taxonomy. There is even a quote from Enrico Fermi about this "If I could remember all names of these particles I'd be a botanist" I just want to know how true is that.
  32. TheQuestionGuy14

    B Can a quantum particle be simulated on a classical computer?

    I'm just curious, is it possible to simulate a quantum particle (so that it is exactly like a real quantum particle) merely using a classical computer? When something is simulated on a classical computer, it's not really actually there, what you see on the screen is just pixels lighting up. The...
  33. warhammer

    Question on Quantum Physics- Probability of finding a particle

    I calculated the complex conjugate of both the given wavefunctions. For ψ1: ∫re^((-2)mod(r)x)dx=1 with upper limit ∞ & lower limit -∞. I replaced the upper and lower limit after breaking down the function inside integration as follows- r*∫e^(2rx)dx from -1/r to 0 and r*e∫e^(-2rx)dx from 0 to...
  34. J

    Particle bouncing between walls

    I thought it would be a good idea to pretend that the walls are stationary and that each time the particle hits a wall, it gets a velocity addition of the velocity of the wall it’s hitting. Using this I ended up at the formula V = initial velocity of particle + n(velocity of left wall) +...
  35. Quantum Alchemy

    B Can entangled particle pairs be measured at the same time?

    Has there been an experiment where 2 particles that are entangled are measured at the same time? If so what was the result? Can any observer occupy the same frame of reference down to an electron? Don't we all exist at different times based on our frame of reference so none of us can share the...
  36. SLTH02

    Determine the potential energy function of the charged particle

    I understand that you need to integrate f(x), and the negative of that is U(x). But the last part of the problem says "Clearly state any assumptions you make." And the answer is just the antiderivative of that f(x) without any constant from integrationHow does that make sense
  37. L

    I A little help with a two particle Hamiltonian

    Hello, I'm working on a project. I need to understand every equation in a paper. I need to calculate the spatial derivative of G (d/dR), a two-particle Hamiltonian. However, G is a function of P- the density matrix and P is a function of R. Is it a "special derivative"? Here is the attached...
  38. F

    I Why is the position of a massive particle not blurred?

    In QM a free micro particle with definite momentum has not definite positions.But why does in classical physics a free particle with definite momentum still have definite positions but not blurred as in QM?(Because we can deduce Classical Physics from QM)
  39. F

    I Scattering of a scalar particle and a Fermion

    Hello everyone, I am working on the following problem: I would like to determine the invariant Matrix element of the process ##\psi\left(p,s\right)+\phi\left(k\right)\rightarrow\psi\left(p',s'\right)+\phi\left(k'\right)## within Yukawa theory, where ##\psi\left(p,s\right)## denotes a fermion...
  40. Amblambert

    Chemistry Quantum Chemistry - Particle in a box

    Here is my attempt at a solution. The thing I am not sure about is the final result of the Shrodinger equation and the n-values that are offered? Did I make a math mistake? Thank you so much for reading through this!
  41. Nonametheone

    Can a virtual particle from a maget accelerate another particle on a linear path?

    Summary: Can a particle accelerator accelerate gaseous fuel? Does space-time differ for detonating ionized fuel moving near the speed of light within a magnetic field such as a particle accelerator?
  42. DoobleD

    I How to get the wavefunction of a single particle in QFT?

    Hi folks, I'm trying to get a grasp on some of the basic concepts of QFT. Specifically, I'm trying to picture what are the actual fields of QFT and how they relate to wavefunctions. There are already many helpful posts about those concepts, here and in other places, but some points are fuzzy...
  43. dRic2

    I Wave function of a scattered particle and cross section

    In Landau-Lifsits's book about non relativistic QM it is said that if I have a particle described by a plane wave ##\phi = e^{ikz}## (I think he choses the ##z## direction for simplicity) the wave function after the scattering event is (far from the scattering event) $$\psi \approx e^{ikz} +...
  44. I

    Minimum separation between incoming proton and alpha particle

    Proton is going towards the ##\alpha## particle. So, I am thinking of using the conservation of energy as the initial kinetic energy of the proton is known and initial interaction potential energy is zero. But, we don't know the kinetic energies of proton and ##\alpha## particle when they are at...
  45. Like Tony Stark

    Particle moving in a rotating disc

    Well, I tried plugging the data in the formula. I know that ##\vec a_b = 0; \vec \omega=3 rad/s ; \vec r## can be calculated using trigonometry. Then I also know that ##v_{relx}= 10 cm/s##, ##a_{relx}=15 cm/s^2##, ##\vec {\dot{\omega}}=-10 rad/s^2##. But how do I get ##v_{rely}## and...
  46. D

    B Is Radioactive Decay Uncaused/Causeless?

    I know that it has a cause! It happens to make the nucleus more stable. But some say it has no cause. I am confused actually.
  47. M

    Determine the change in direction of a particle

    Note: I don't know if this actually qualifies as advanced physics, it probably doesn't. It's a review problem in a non-introductory class but I can't solve it so... Beginning with the hint, I know that the x and y components of velocity don't change when the particle moves from z < 0 to z > 0...
  48. P

    I Identify the charge and strangeness of particle Y

    Ive included question and thinking in the attachments. Many Thanks
  49. W

    Lagrange Equations of Motion for a particle in a vessel

    The final answer should have a negative b^2⋅r(dot)^2⋅r term but I have no idea how that term would become negative. Also I know for a fact that my Lagrangian is correct.
  50. W

    Lagrange Equations of Motion for a particle in a vessel

    I start out by substituting rcos(Θ) and rsin(Θ) for x and y respectively. This gives me z=(b/2)r^2. The Lagrangian of this system is (1/2)m(rdot^2+r^2⋅Θdot^2+zdot^2)-mgz. (rdot and such is the time derivative of said variable). I then find the time derivative of z, giving me zdot=br⋅rdot and...
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