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. J

    Showing particle travels at constant speed (geometry)

    Homework Statement the trajectory γ: ℝ→ℝ3 of a charged particle moving in a uniform magnetic field satisfies the differential equation γ''= B x γ'(t) . where B = (B1, B2, B3) is a constant 3-vector describing the magnetic field, and × denotes the vector product. (a) Show that the particle...
  2. LarryS

    Particle Accelerator for Uncharged Particles?

    Particle accelerators use the electromagnetic field to accelerate charged particles. Would it be possible to build a particle accelerator for uncharged particles? Say we are given a narrow beam of neutrons. How could we accelerate them so that the accelerated particles were still in a...
  3. D

    Average acceleration of the a particle in circular motion

    Homework Statement A particle of mass ##m## moves along a circle of radius ##R##. The modulus of the average vector of the force acting on the particle over the distance equal to a quarter of the circle is: zero if the particle moves with uniform speed ##v##. ##\dfrac{\sqrt2mv^2}{\pi R}## if...
  4. Dusty912

    Determining work of a 3 particle system

    Homework Statement on a spherical astroid with a radius of 500km and an acceleration due to gravity of 3.0m/s2 How far from the surface will a particle go if it leaves the asteroid’s surface with a radial speed of 1000m/s? Homework Equations conservation of energy Ui + ki=Uf +kf U=-(GmM)/r...
  5. W

    Velocity and acceleration of a particle of a fluid

    Homework Statement Homework Equations x = (x1,x2,x3) are the coordinates of the current configuration and X = (X1,X2,X3) are the coordinates of the reference configuration where x = y(X,t) where y is a deformation of X. The Attempt at a Solution (a) taking the partial derivatives of xi with...
  6. Thejas15101998

    I Why can't we use negative values of n in the 1D particle in a box system?

    In the 1D particle in a box system why don't we take negative integer values of n besides the positive integer values? Well I thought about it and I think the reason is that during derivation we get ka=n (wavelength ) and thus n being negative implies that wavelength is negative hence contradiction.
  7. S

    Determine the energy of an alpha particle

    I have been asked to determine the energy in MeV of an alpha particle and an Rn nucleus in the decay of Ra-226 using the conservation of energy and momentum. (assume Ra is at rest) Here is what i have done, I am just wondering if i did it properly. Thanks for your help :) Ek=kinetic energy...
  8. C

    I Wave particle duality and phonons

    I was reading the thread about wave particle duality linked from the newsletter, and I noticed it said (to use my own words) that the conflict between wave and particle dynamics can be avoided by using operator dynamics instead. Unfortunately, in the case of phonons, I've never seen a...
  9. F

    B Is wave particle duality really wrong?

    Can all seasoned physicists please confirm if it is true that wave particle duality is really wrong as when Bill stated in the decoherence branches thread "This is a little different than what you will find in a beginner text becauise it doesn't use the wave particle duality which is wrong - but...
  10. D

    Particle motion when wrapped around drum; elastic string

    Homework Statement A uniform cylindrical drum of mass M and radius a is free to rotate about its axis, which i is horizontal. An elastic cable of negligible mass and length l is wrapped around the drum and carries on its free end a mass m. The cable has elastic potential energy \tfrac12...
  11. M

    Motion of a charged particle in an uniform electric field

    Homework Statement Imagine a particle with charge +Q moving with constant horizontal velocity passing perpendicular to electric field between two parallel plates. The length of the plates is L. Therefore, is the time spent in the field (well, between the plates), simply the length/horizontal...
  12. R

    Solve Particle Equilibrium Homework Statement

    Homework Statement If the 4.4-kg block is suspended from the pulley B and the sag of the cord is d = 0.15 m, determine the force in cord ABC. Neglect the size of the pulley. (Figure 1) Express your answer to three significant figures and include the appropriate units.Homework EquationsThe...
  13. Mr Davis 97

    How Does Reflecting a Particle Stream Affect the Force on a Surface?

    Homework Statement A one-dimensional stream of particles of mass ##m## with density ##\lambda## particles per unit length, moving with speed ##v##, reflects back from a surface, leaving with a different speed ##v'##, as shown. Find the force on the surface Homework EquationsThe Attempt at a...
  14. TheSodesa

    Maximum change in the kinetic energy of a particle

    Homework Statement Show that the largest possible change in the kinetic energy , ##\Delta E_{kin}##, of a particle of mass ##m## running into another particle of mass ##M## at rest in the lab coordinate system is \Delta E_{kin} = \frac{-4AE_{kin}}{(1+A)^{2}}, where ##A = \frac{M}{m}##...
  15. Titan97

    Probability of finding a particle in an infinite well

    Homework Statement For the particle in a box given in the above question, what is the probability of finding the electron between (i) x = 0.49 and 0.51, (ii) x = 0 and 0.020 and (ii) x=0.24 and 0.26 ( x in nm) for both n=1 and n=2. Rationalize your answers. Homework Equations...
  16. H

    B Aerogel comet particle capture experiment?

    some years ago it was big news when some aerogel bulk launched at the tail of a comet and bits of the comet dust got stuck in the gel. this was going to be recovered somehow and analysed. I do not know any more about that particular experiment but it died out of the mainstream news. anyone...
  17. Vitani11

    I Is Light Really a Particle or a Wave? Exploring the Confusion in Modern Physics

    We've learned Q&M in modern physics but I need to make sure I'm getting this concept right... So the photoelectric effect demonstrated the fact that a photon (wave) can knock an electron out of a metal, which could only happen if a photon was a particle. So much for photons being waves. I get...
  18. J

    Decelerating charged particle and energy conservation

    Consider a charged particle moving with velocity v, having the energy 1/2 m v^2. Now we deccelerate the particle very quickly; so quickly that the radiated energy is greater than the kinetic energy (it can be arbitrarily large). Note also that energy obtained from decceleration is positive...
  19. B

    A charged particle entering a magnetic field at an angle -- is work done?

    Hello PF's members I know a magnetic field doesn't work on charged particles if magnetic field being perpendicular to the velocity of the particles. also i know magnetic field doesn't work if a charged particle enters with right angle into the field. But suppose that a charged particle like...
  20. Elvis 123456789

    Photon beam is incident on a proton target produces a particle

    Homework Statement A photon beam is incident on a proton target (at rest). Particle X (and nothing else) with rest mass M=1.232GeV/c2 is then produced. Use m_p =0.938GeV/c2 as the proton mass. a) What is the energy of the photon beam, in terms of GeV? b) What is the momentum of the moving...
  21. moenste

    Particle moving with simple harmonic motion

    Homework Statement A particle moves with simple harmonic motion in a straight line with amplitude 0.05 m and period 12 s. Find: (a) the maximum speed, (b) the maximum acceleration, of the particle. Write down the values of the constants P and Q in the equation x / m = P sin [Q (t / s)] which...
  22. A

    Teaching particle physics in basic education

    Hi guys! I'm doing a research about teaching elementary particles in the middle school, something that isn't the reality in my country. Despite of the research in Physics Teaching be a lot advanced, the proposals made by them are not applied in the practice of the teachers. I want to propose...
  23. D

    Particle shot from a height h on Earth

    Homework Statement A cannon that is capable of firing a shell at speed V_0 is mounted on a vertical tower of height h that overlooks a level plain below. (a) Show that the elevation angle \alpha at which the cannon must be set to achieve maximum range is given by the expression...
  24. D

    Kinematic Particle Homework: Deriving a_r and a_theta

    Homework Statement Homework Equations Formulas for a_r and a_theta. The Attempt at a Solution I got the second derative of r but I think the fluxie v is a mistake. I am sure that \dot{v} =a\ , right?
  25. Titan97

    B Position of a particle immediately after a measurement

    Say a particle was measured to be at a point C. Immediately after this, if i make another measurement, its given in griffith's book that the particle will still be found at C. Isn't this only possible if the particle was at rest?
  26. moenste

    Reaction on the particle in terms of angular velocity

    Homework Statement A particle is attached by means of a light inextensible string to a point 0.4 m above a smooth horizontal table. The particle moves on the table in a circle of radius 0.3 m with angular velocity ω. Find the reaction on the particle in terms of ω. Hence find the maximum...
  27. moenste

    Speed of the particle at a height h

    Homework Statement A particle is projected with speed v at an angle α to the horizontal. Find the speed of the particle when it is at a height h. Answer: √v2 - 2gh 2. The attempt at a solution a. Since PE gained is KE lost we need to find KE and PE. KE = 0.5 * m * (v sin α)2 (the vertical...
  28. B

    Position of a charged particle

    Homework Statement Two particles 1 and 2, each carrying 6.0 nC of charge, are located along an x axis, one particle atx=−30 mm and the other at x = 30 mm. Where along the y-axis is a particle 3 carrying a charge of +2.0 nC if it experiences an electric force of 6.9 × 10^−5 N ȷ^? Homework...
  29. mihailo

    Average velocity of free particle

    Homework Statement The wave function is given as Ψ(x,t) = Ae^[i(k1x-ω1t)] + Ae^[i(k2x-ω2t)]. Show that particle average velocity Vav = ħ(k1+k2)/2m equals ω2-ω1/k2-k1. Average momentum of the particle is Pav = ħ(k2+k1)/2. Homework Equations p = ħk E=ħω K = 1/2 * mV^2 The Attempt at a Solution...
  30. D

    I How do Particle Exchange Forces Create Attractive Forces?

    So sorry to post what seems to be a well worn question. So the 4 forces of nature work by "particle exchange" ? Yes we understand the maths of "Fields" and we have the elegance of Maxwell and Newton/Einstein and these mathematical descriptions lead us to force exchange particles which can...
  31. majormuss

    I Understanding the wavefunction for a free particle

    Hi everybody, I was reading about the free particle in a textbook and I got confused by the line: "If we adopt the convention that k and k are real, then the only oscillating exponentials are the eigenfuntions with positive energy" [Also see the attached picture with the...
  32. H

    General pathline of a particle x at point epsilon at time ta

    Homework Statement Show that the path line of a particle at point x currently, and point ξ at time τ is given by ξ(τ) = x + (τ-t)Lx Homework Equations Pathline is solution to dx/dt = u x(t)|t=τ = X L is the velocity gradient and is a 2nd order tensor Lij = dui/dxj The Attempt at a...
  33. Elvis 123456789

    Another relativistic particle decay question

    Homework Statement Unstable particles cannot live very long. Their mean life time t is defined by N(t) = N0e−t/τ , i.e., after a time of t, the number of particles left is N0/e. (For muons, τ=2.2µs.) Due to time dilation and length contraction, unstable particles can still travel far if their...
  34. Elvis 123456789

    Relativistic particle decay

    Homework Statement Unstable particles cannot live very long. Their mean life time t is defined by N(t) = N0e−t/τ , i.e., after a time of t, the number of particles left is N0/e. (For muons, τ=2.2µs.) Due to time dilation and length contraction, unstable particles can still travel far if their...
  35. A

    Coulombs law and particle charges

    Homework Statement An electron and another particle experience an attractive force of 0.0096 N when they are 0.001m apart. what is the charge of the other particle q1= -1.602E-19 F=-0.0096 r=0.001 2. Relevant equation how do you find q2 out to solve the equation The Attempt at a Solution
  36. Drakkith

    I Wavelength of a Stationary Particle

    We were going over the basics of the photoelectric effect today in my solid state chemistry class when my instructor gave us a question asking what the wavelength of an ejected electron was. We worked through the question and got the answer, but that got me thinking. If the wavelength is...
  37. U

    Propulsion by Cosmic Particle Deflection: A New Idea?

    What about the attached as a means of propulsion? It would be a spacecraft with a long magnet in the front. Attached on one side by boons the magnet would have a reflector/deflector or shield of some type e.g. aluminum. In interstellar space there would be charged cosmic particles moving in...
  38. Milind Chakraborty

    A Charged Particle moving in Uniform Magnetic Field

    Homework Statement Problem given in the image attached. Uniform Magnetic Field : B Positive Charge : q Uniform Velocity : v Mass : m Charged particle enters the magnetic field making an angle θ with the plane perpendicular to the magnetic field. Width of the region of Magnetic field : d d <...
  39. A

    I 'Real particle and virtual particle interactions' Part 2....

    Hi folks, I number of years ago, I asked a question about real particles interacting with virtual particles - since then, I've learned a little bit (maybe not too much :-), but I'm still curious about one thing. Original thread here...
  40. T

    Calculating the velocity given the position of the particle

    Homework Statement A particle moves with constant velocity along the curve r = e^(θ) and z = r (cylindrical coordinates). The speed, v, is constant. a) Calculate the velocity and acceleration of the particle in terms of θ and v. b) Show that the velocity and acceleration are perpendicular...
  41. V

    Constant force acting on a particle

    Homework Statement Homework EquationsThe Attempt at a Solution If I consider a coordinate system with the -Y axis along the direction of force and X axis along a line perpendicular to it (except the direction of velocity vector) then this problem is equivalent to the usual projectile motion...
  42. K

    I What happens when an anti-particle collides with our body?

    We know that matter and anti matter annihilate each other if they come together. Then what would happen in a collision of a anti particle with our body?
  43. K

    Particle confined to move on the surface of sphere

    Homework Statement what will be Lagrange,s equation of motion for a particle confined to move on surface of sphere whose radius is expanding such that Homework Equations Euler-lagranges equation of motion d/dt(∂L/∂{dq/dt})-∂L/∂q=0 The Attempt at a Solution Z=(R+R0e^at)cosθ...
  44. R

    I What is the role of entropy in particle decay theory?

    Maybe my question is a bit more philosophical than scientific. In the macroscopic world entropy means that things become more chaotic and less orderly as they decay. It seems to me somewhat paradoxical that in the quantum world lower generation particles "decay" into the first generation...
  45. J

    I Spin 1/2 particle emitting spin 2 particle?

    As I understand it (e.g. from discussions around the Fermi field theory of the nuclear force), a spin 1/2 particle can emit a spin-1 particle and simultaneously flip its spin (say, spin +1/2 -> photon +1 & spin -1/2); but how does this work with spin-2 particles? Does it need to emit pairs in...
  46. H

    Relativistic speed of a particle

    Homework Statement Find the speed of a particle whose total energy is twice its rest energy. Homework Equations E2 = p2c2 +m2c4 The Attempt at a Solution 4m2c4 = p2c2 +m2c4 3m2c4 = p2c2 SQRT(3)mc2 = pc SQRT(3)mc = p SQRT(3)mc = mv SQRT(3)c = v I know I can use E = gamma*mc2 to get the...
  47. O

    Free particle wave function confusion.

    Hi! I'm currently studying Griffith's fantastic book on QM, and I'm confused for a bit about the wave function for a free particle. Here's what I think so far; for a free particle, there are no stationary states, so therefore we can't solve the SE with...
  48. S

    Lie algebra for particle physics

    Hello! I am sorry that this questions is not actually directly related to physics, but, can anyone recommend me a good book about abstract algebra (basically lie algebra, representation theory etc.) used in physics? I have tried for a long time to find something online but I haven't find a...
  49. B

    B Particle & apparatus outputs

    Please give me any experimental setup or measurement apparatus already available that can output by amplifying the result of a given instance when a single electron has spin up or down... and changing between the two spins which can change the outputs... or any other observable of a single...
  50. Chris Frisella

    I What test for determing particle spin?

    Perhaps a silly question, but... As I understand it, if a particle has a 1/2 spin, it must be spun 720 degrees for it to arrive at its original orientation. What experiment spins a particle like this? Has there been one that actually spins a particle 720 degrees and checks its orientation? Or...
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