Momentum Definition and 1000 Threads

  1. PeroK

    Angular Momentum in Spherical Coordinates

    I've started on "Noether's Theorem" by Neuenschwander. This is page 35 of the 2011 edition. We have the Lagrangian for a central force: ##L = \frac12 m(\dot{r}^2 + r^2 \dot{\theta}^2 + r \dot{\phi}^2 \sin^2 \theta) - U(r)## Which gives the canonical momenta: ##p_{\theta} = mr^2...
  2. chmodfree

    I Generalized Momentum is a linear functional of Velocity?

    Generalized momentum is covariant while velocity is contravariant in coordinate transformation on configuration space, thus they are defined in the tangent bundle and cotangent bundle respectively. Question: Is that means the momentum is a linear functional of velocity? If so, the way to...
  3. Decimal

    I Value of orbital angular momentum for two particles

    Hello, I encountered the following statement in my lecture notes and there is a couple of things I don't understand:"Let's consider two particles with spins ##s_1 = \frac{1}{2}## and ## s_2 = 1## with a spherically symmetric interaction potential. Assume these two particles are in a two...
  4. L

    Simple Ice Skater with Conservation of Angular Momentum

    Homework Statement Not a HW problem, but a "me re-thinking things" problem. Please tell me where my thinking is flawed: You have an ice skater with no net external torques acting on him/her. (We are analyzing the time after they have to get an external torque on them by pushing off of the...
  5. maxd23

    A Nuclear Reaction: Determining the velocity of neutrons

    Homework Statement Fission, the process that supplies energy in nuclear power plants, occurs when a heavy nucleus is split into two medium-sized nuclei. One such reaction occurs when a neutron colliding with a 235U (uranium) nucleus splits that nucleus into a 141Ba (barium) nucleus and a 92Kr...
  6. delta76

    B Can I Apply Physics Concepts to a Zipline Ride?

    Hey! I am new on the forum and I joined because I really enjoy physics but I have a horrible teacher. I was wondering if anyone could help me on a question how do I find the velocity at the end of the zipline? how do I find the momentum of the object going down the zipline after it is...
  7. S

    Conservation of angular momentum

    Homework Statement A uniform thin rod AB is equipped at both ends with the hooks as shown in the figure and is supported by a frictionless horizontal table. Initially the rod is hooked at A to a fixed pin C about which it rotates with a constant angular velocity w1 . Suddenly end B of the rod...
  8. A

    Finding Momentum when giving the mass and height

    A 50.0-kg male dancer leaps 0.32 m high. (a) With what momentum does he reach the ground? I know that to find momentum the equation is P = mv, but I only have the mass and distance. I have tried finding the time (D = 1/2at^2) and later used that time to find the velocity (v = d/t). I later used...
  9. J

    I Calculating the number of energy states using momentum space

    A question came up about deducing the number of possible energy states within a certain momentum ##p## using momentum space. To make my question easier to understand, I deliberately chose ##p## and not a particular increment ##dp## and I assume a 2 dimensional momentum space with coordinates...
  10. Javier Lopez

    A What is the key parameter in fusion: momentum or energy?

    The released products of a transmutation reaction (I say transmutation when 2 particles reacts to generate more than one) follows the conservation of kinetic energy law. Also particles moving in opposite direction can have equal speed one with respect the other than rather if one of them is...
  11. Krushnaraj Pandya

    Angular momentum of particle about the origin

    Homework Statement A particle (5 kg) moves with constant velocity 2 m/s along the straight line 2y=3x+4, the angular momentum of the particle about origin is? Homework Equations L=r x p The Attempt at a Solution For a 2d problem we take the component of velocity perpendicular to the point...
  12. C

    Conservation of Angular Momentum on a rotating disc

    I have a disc that is rotating due to air being blown at its outer radius. The incoming relative velocity of the air is high, therefore the effect of friction supersedes the effect of conservation of angular momentum. The tangential portion of this velocity decreases due to the friction as it...
  13. Krushnaraj Pandya

    Conditions for conservation of momentum

    Homework Statement Consider a classic wedge and block system, (block on top of wedge(inclination theta)). there is friction between the block and wedge (not enough to prevent block from sliding). All other surfaces are smooth. For the motion that follows after releasing the block from rest, is...
  14. Henrique Orlandini

    Terminal velocity of a skier using a Momentum Balance

    Homework Statement [/B] A skier (mass M = 100 kg) going down a slope with inclination θ = 30°, sliding in a fluid-like snow (viscosity μ = 100 mPa*s) of thickness h = 0.01 m, using a pair of skis, each one with a surface area of As = 0.15 m2, reaches terminal velocity vt after some distance...
  15. J

    Angular momentum after a collision

    Homework Statement A disk of radius ##r## and mass ##m## rolls down an inclined plan. It reaches the end of the plane with velocity ##v_{f}## and collides with a vertical rod of length ##L## and mass ##M## sticking with it. See figure. What is the angular momentum magnitude and direction...
  16. P

    Eigenfunction of momentum and operators

    Homework Statement Homework Equations ##\hat{P}= -ih d/dx## The Attempt at a Solution To actually obtain ##\psi_{p_0}## I guess one can apply the momentum operator on the spatial wavefunction. If we consider a free particle (V=0) we can easily get obtain ##\psi = e^{\pm i kx}##, where ##k=...
  17. gibberingmouther

    Momentum of a System and External Forces

    So Pearson is telling me that, basically, the ratio of internal to external forces and the briefness of the time interval is what determines whether the external forces on a system whose momentum we're studying will affect whether we can obtain a decent approximation of the momenta of the...
  18. J

    Angular momentum conservation in collision with a nail

    Homework Statement A ball of mass ##m## is attached to a massless string of length ##L##. The ball is released from rest as shown in the figure and as it reaches the bottom of the circle, the string wraps around a nail which is a distance ##d## below the center of the circle. What is the...
  19. W

    Recoil Proton Momentum Spectrum in Neutron Decay

    I wish to draw the proton momentum spectrum by transforming the energy spectrum of recoil protons. I have calculated the energy spectrum using Nachtmann's spectrum: wp=g1[T]+a*g2[T] Where: g1[T]=(1 - x2/σ[T])2 * Sqrt[1 - σ[T]] * (4*(1 + x2/σ[T]) - (4/3*(σ[T] - x2)/σ[T])*(1 - σ[T])); g2[T]=(1 -...
  20. J

    Variable mass beans falling on a platform

    Homework Statement A spigot pours beans onto a scale platform. At a time t = 0.0 sec, the spigot is opened and beans begins to pour out (with initial velocity 0) at a rate of 1.00 kg/sec onto the platform from a height of 10.0 m above. (a) At t = 10.0 sec, what is the weight of beans on the...
  21. P

    I Momentum of a stationary particle/wave?

    We are all familiar with Heisenbergs uncertainty principle. When we determine the position of a particle or wave, the uncertainty of momentum reach infinity. So let's say I have a machine that measures the position very very precisely. Then the uncertainty of this non-moving particles momentum...
  22. E

    B Momentum in special relativity

    Although I thought that I understand special relativity enough, I cannot now clearly answer on the following question: What is the most direct derivation, why momentum in special relativity is ##p=\gamma m v##, where ##v## is velocity of the rocket? Let us assume that Lorentz equations are...
  23. D

    Normalization of the Fourier transform

    Homework Statement The Fourier transfrom of the wave function is given by $$\Phi(p) = \frac{N}{(1+\frac{a_0^2p^2}{\hbar^2})^2}$$ where ##p:=|\vec{p}|## in 3 dimensions. Find N, choosing N to be a positive real number. Homework Equations $$\int d^3\vec{p}|\Phi(p)|^2=1$$ , over all p in the 3...
  24. H

    Puzzle: propagation of momentum in water

    Hello again Physics Forums! I have a question about fluid dynamics. Perhaps someone here can help me out. I am trying to understand how a plume of water moving at some speed carries momentum within a body of water. For instance the ‘exhaust’ from a submarine propeller. I am having a hard time...
  25. Rabindranath

    Angular momentum operator for 2-D harmonic oscillator

    1. The problem statement I want to write the angular momentum operator ##L## for a 2-dimensional harmonic oscillator, in terms of its ladder operators, ##a_x##, ##a_y##, ##a_x^\dagger## & ##a_y^\dagger##, and then prove that this commutes with its Hamiltonian. The Attempt at a Solution I get...
  26. F

    Momentum and collision related problem

    25.0-kg dog is trapped on a rock in the middle of a narrow river. A 66.0-kg rescuer has assembled a swing with negligible mass that she will use to swing down and catch the trapped dog at the bottom of her swing, and then continue swinging to the other side of the river. The ledge that the...
  27. J

    Angular momentum relative to the origin

    Homework Statement A 2.4 kg particle-like object moves in a plane with velocity components vx = 25 m/s and vy = 80 m/s as it passes through the point with (x, y)coordinates of (3.0, −4.0) m. (Express your answers in vector form.) (a) What is its angular momentum relative to the origin at this...
  28. J

    When the spring is maximally extended, find v_1f

    Homework Statement A mass m_1, initially moving at a speed v_0, collides with and sticks to a spring attached to a second, initially stationary mass m_2. The two masses continue to move to the right on a frictionless surface as the length of the spring oscillates. At the instant that the...
  29. R

    Physics 30 question about conservation of momentum

    Homework Statement A space person is motionless a distance of 500m away from the safety of the spacecraft . The person has exactly 11.32min of air left and the person's mass is 103.2kg, including equipment. The person throws a phaser at a velocity of 50.2km/h away from the spacecraft in order...
  30. M

    Conservation of angular momentum

    Homework Statement A rod of length D sits at rest on a friction less table. A ball of mass M strikes the end of the rod with a speed V and rebounds with a speed 3v/4 causing the rod to rotate counterclockwise around a fixed axis at one end. The rotational inertia of the rod is I Homework...
  31. J

    Rotational Momentum: Calculating Angular Speed After Cockroach Stops

    Homework Statement A Texas cockroach of mass 0.17 kg runs counterclockwise around the rim of a lazy Susan (a circular disk mounted on a vertical axle) that has radius 15 cm,rotational inertia 4.9 ✕ 10^−3 kg · m2, and frictionless bearings. The cockroach's speed (relative to the ground) is 2.0...
  32. M

    Momentum transport in gases in 2d

    I was trying to understand the momentum transport between gas molecules in 2d.In the image below, it is stated that half of the molecules move up(positive velocity in y direction) and half negative.But the author didnt explain why he assumed it.
  33. F

    Momentum equation and open channel flow

    Homework Statement Determine y2 (ft)and v2 (ft/s) using the momentum principle assume widths are the same at 1 and 2 Homework Equations from what i remember in my past fluids class, the momentum equation is: Force = Qvout - Qvin assuming same density and direction However in my lecture the...
  34. T

    Pressure and temperature due to frictional or momentum input

    Hi, I have a hypothetical question: We have a fan which has no internal dissipation - electrical or mechanical. The fan is made to run in an adiabatically sealed room. The internal energy of the air in the room increases due to work input. This work input increases the temperature and...
  35. J

    Momentum vs Work: Find Out in Super Hero Experiment

    All, I started this strange little thought experiment this morning, but I'm not quite sure what I'm missing. Here's the problem I solved (this is not homework, BTW): Find the speed at which a super hero (mass=76.0 kg) must fly into a train (mass = 19,537 kg) traveling at 35 m/s to stop it ...
  36. dRic2

    Bulk Angular Momentum: Definition & Explanation

    According to the book "transport phenomena" by Lightfoot, Byron and Stewart if you take the cross product of the equation of motion (for very small element of fluid) and the position vector ##r## you get the equation of change of angular momentum. After some manipulation of vectors and tensors...
  37. J

    Without Lagrangian, show that angular momentum is conserved

    Homework Statement I'd like to show, if possible, that rotational invariance about some axis implies that angular momentum about that axis is conserved without using the Lagrangian formalism or Noether's theorem. The only proofs I have been able to find use a Lagrangian approach and I'm...
  38. 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...
  39. W

    I Phonons and Crystal Momentum: Conservation and Quantization

    Hi all, I have a few questions. Thanks in advance! Phonons: Can phonons be thought of as a quantised wave of sound, in the same manner photons being a quantised light wave? Also, can they be taken as particles of sound in the same way that photons can be particles of light? Crystal momentum...
  40. S

    I Understanding Spin & Angular Momentum in Quantum Mechanics

    Hello! I got a bit confused about the fact that the whole the description of spin (and angular momentum) is done in the z direction. So, if we are told that a system of 2 particles is in a singlet state i.e. $$\frac{\uparrow \downarrow -\downarrow \uparrow }{2}$$ does this mean that measuring...
  41. Jonathan1218

    Why is angular momentum conserved?

    My intuition is if an object is orbiting a centre, it is accelerating as the direction of its vector constantly changes, i.e a ball orbiting a stick because they are tied by a string. I don't understand why Earth's spin does not slow down, if we think of Earth as lots of individual atoms, those...
  42. C

    Other I can't solve questions related to conservation of momentum

    I'm a passout from school taking a gap year. I find the concept of conservation of momentum exceedingly difficult. Each question - and sometimes each part of a question, if a question has different parts - requires us to choose different systems each time. I look at the solution, and think I...
  43. L

    A Momentum calculation of a rotating rod

    ##\ \ \ \ \ ##Calculate the 4 momentum of a rotating rod. We divide it into 4 parts. The part 1 is the work of predecessors. ##\ \ \ \ \ ##In Special relativity, the motion of rod AB (which is an object in non inertial motion) can be described in an inertial reference frame and the motion of rod...
  44. jxj

    Isolating Variable in Equation for conservation of momentum

    Homework Statement So the problem is trying to isolate mA in the equation for momentum (only focusing on top formula, not bottom hehe) basically by solving the equation I assume. My teacher said because the vA and vB on the right were prime they could not be combined so I'm having trouble...
  45. B

    Schwinger's model of angular momentum

    Homework Statement Consider two pairs of operators Xα, Pα, with α=1,2, that satisfy the commutation relationships [Xα,Pβ]=ihδαβ,[Xα,Xβ]=0,[Pα,Pβ]=0. These are two copies of the canonical algebra of the phase space. a) Define the operators $$a_\alpha =...
  46. S

    Can someone help me to calculate the velocity at Stack Tip?

    Homework Statement How can we calculate the velocity at stack tip if the distance of larger diameter is 2.5 m? I think i cannot use the equation of V1A1 = V2A2 because they may have some effect from 2.5 m of distance. Thank you very much. Homework Equations Q1=Q2 The Attempt at a Solution...
  47. Sandeep T S

    Why is momentum conserved in elastic and inelastic collisions?

    Why momentum conserved in elastic collision and inelastic collision? Please attach mathematical proof too
  48. S

    Total Angular Momentum of an odd-parity shell-model state

    Homework Statement A certain odd-parity shell-model state can hold up to a maximum of 4 nucleons. What are its values of J and L? What about an odd-parity shell-model state with a maximum of 6 nucleons? Homework Equations Parity = (-1)L J = L+S Total angular momentum, J, is equal to orbital...
  49. PhysicsIsKillingMe

    Which Force is Represented by the Gradient of the Ball-Wall Collision Graph?

    Problem goes: A rubber ball, traveling in a horizontal direction, strikes a vertical wall. It rebounds at right angles to the wall. The graph below illustrates the variation of the ball’s momentum p with time t when the ball is in contact with the wall. Which of the following statements is...
  50. Muhammad Danish

    B Lead vs. Rubber Bullets: Which is More Effective in Stopping a Bear?

    Which bullet of same momentum is more effective in knocking a bear down? Lead bullet or rubber bullet?
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