Conservation of momentum Definition and 757 Threads

In Newtonian mechanics, linear momentum, translational momentum, or simply momentum (pl. momenta) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If m is an object's mass and v is its velocity (also a vector quantity), then the object's momentum is





p

=
m

v

.


{\displaystyle \mathbf {p} =m\mathbf {v} .}
In SI units, momentum is measured in kilogram meters per second (kg⋅m/s).
Newton's second law of motion states that the rate of change of a body's momentum is equal to the net force acting on it. Momentum depends on the frame of reference, but in any inertial frame it is a conserved quantity, meaning that if a closed system is not affected by external forces, its total linear momentum does not change. Momentum is also conserved in special relativity (with a modified formula) and, in a modified form, in electrodynamics, quantum mechanics, quantum field theory, and general relativity. It is an expression of one of the fundamental symmetries of space and time: translational symmetry.
Advanced formulations of classical mechanics, Lagrangian and Hamiltonian mechanics, allow one to choose coordinate systems that incorporate symmetries and constraints. In these systems the conserved quantity is generalized momentum, and in general this is different from the kinetic momentum defined above. The concept of generalized momentum is carried over into quantum mechanics, where it becomes an operator on a wave function. The momentum and position operators are related by the Heisenberg uncertainty principle.
In continuous systems such as electromagnetic fields, fluid dynamics and deformable bodies, a momentum density can be defined, and a continuum version of the conservation of momentum leads to equations such as the Navier–Stokes equations for fluids or the Cauchy momentum equation for deformable solids or fluids.

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  1. D

    Classical mechanics and conservation of momentum

    Heres the question: A car of mass m = 1200 kg and length l = 4 m is positioned such that its rear end is at the end of a flat-top boat of massM = 8000 kg and length L = 18 m. Both the car and the boat are initially at rest and can be approximated as uniform in their mass distributions and the...
  2. M

    Homework: conservation of momentum

    Hi, could you please help me with following: ---------- two boats traveling in opposite direction with speed v1 and v2 when they are passing by they interchange a parcel of same mass M=50kg as a result second boat stops and first boat continue traveling in same direction with speed...
  3. S

    Mechanics: conservation of momentum problem

    Here's the problem: An atom of mass 2mp with an anitial velocity vo undergos an elastic collision with an atom at rest with mass 3mp. After the collision, the first atoms trajectory deviates 30 degrees from the initial. What angle does the second atom travel from the first atoms initial...
  4. M

    Inertia and conservation of momentum

    How are inertia (Newton's first law) and the law of conservation of linear momentum related? Also, how does Newton's first law for rotation (rotational inertia or moment of inertia) related to the law of conservation of angular momentum?
  5. D

    Conservation of Momentum difficulty

    I'm not sure if i did this problem correctly. Could someone check it over. A 730-N man stands in the middle of a frozen pond of a radius of 5.0 m. He is unable to get to the other side because of a lack of friction between his shoes and the ice. To overcome this difficulty, he throws his 1.2...
  6. S

    Conservation of energy and conservation of momentum

    Using both cinservation of energy and conservation of momentum, show that the spring constant k is given by k=2mg/H[1+mg/(m+M)H] I thought that this would go easier if I rewrote the expression for kinetic energy in terms of momentum, but I can't exactly get around figuring the change in...
  7. K

    Conservation of Momentum and energy problem help

    SOmeone explain to me this because I am lost. i got 2 masses one velecity. the equation is like is mass times volocity + mass times velocity=0 122kg*22m/s+14kg*v=0 I made these numbers up what i do is multiply and add then move my anwser to the other side becoming negative but that doesn't...
  8. T

    Conservation of Momentum - true?

    I’m currently involved in a debate with a few folks regarding the validity of the Conservation of Momentum principle. One demonstration of its failure was dropping a book. The book begins with no momentum, gains momentum, then looses it and again has none (when it hits the floor). Of...
  9. X

    Why did our conservation of momentum experiment have unexpected results?

    I was doing a lab one day in school and me and my teacher noticed something this isn't homework. We were wondering about conservation of momentum in the lab. The way it was done was we attached a small little ramp on the table. On the ramp we put a marble and let it slide down the ramp and onto...
  10. H

    How Do Collisions Affect Momentum in Physics Problems?

    Can anyone help me with these two problems? Thank-you 1.) Two carts with masses of 15.5 kg and 6.0 kg, respectively, move in opposite directions on a frictionless horizontal track with speeds of 7.0 m/s and 2.0 m/s, respectively. The carts stick together after colliding head-on. Find the...
  11. C

    Conservation of momentum and energy problem

    I read the answer of it, but I don't get why the answer is that. And the answer is 1/2 M gun x (M bullet * V bullet / M gun)^2 - 1/2 M gun+you x (M bullet * V bullet/ M gun+you) ^2thx!
  12. E

    Conservation of momentum vs conservation of kinetic energy

    if i hit a still 1 kg billiard ball with another 1kg ball at 10 m/s the second ball will stop and the first ball will acquire a speed of 10 m/s, both conservation of momentum and energy acomplish but if i hit a still 10 kg ball with a 1 kg ball at 10 m/s the 10 kg ball will acquire a speed of...
  13. E

    Quantum Mechanics and conservation of momentum

    I need help getting started solving the following. Show that when the recoil kinetic energy of the atom, p^2/2M, is taken into account the frequency of a photon emitted in a transition between two atomic levels of energy difference delta-E is reduced by a factor which is approximately (1 -...
  14. W

    Is this in contradiction with the theorem of conservation of momentum?

    The theorem of conservation of momentum states that the quantity of momentum is always the same. When two objects collide, during the interval of time they touch each other their velocities are the same but are in the same time changing, if they are both changing but remaining equivalent, why is...
  15. V

    Conservation of momentum of a neutron

    A He4 nucleus, with a mass of 4 amu moving with speed v breaks up into a neutron 1amu and a He3 nucleus 3amu . If the neutron moves in a direction perpendicular to the direction of motion of the original He4 nucleus with speed 3v, what is the speed of the He3 nucleus? if the neutron moves...
  16. E

    Change in total kinetic energy in a conservation of momentum problem?

    Question: On a frictionless, horizontal air table, puck A (with mass m_1) is moving toward puck B (with mass m_2), that is initially at rest. After the collision, puck A has a velocity of v_1 to the left, and puck B has velocity v_2 to the right. 1. What was the speed of puck A before the...
  17. E

    How Does Catching a Ball Illustrate the Conservation of Momentum?

    Somebody throws me a ball with mass .400 kg at velocity 10.0 m/s. My mass is 65.5 kg. 1. If I catch the ball, with what speed do the ball and I move afterwards? Shouldn't the answer be (.400)(10.0=(65.9)(v_2), where v_2=.0607m/s?
  18. D

    Quick Question - Conservation of Momentum

    ball with a mass of 0.10 kg has a velocity of 7 m/s. It strikes a concrete wall perpendicularly and bounces straight back with velocity of 4 m/s. The change in the ball's momentum was equal to Response Answer Choices a. 0.30 kg m/s b. 0.10 kg m/s c. 0.40 kg m/s d. 1.1 kg m/s...
  19. T

    Conservation of momentum in two dimensions?

    Hi all, I'm having a tough time with a below question and would like some hints on where I've gone wrong if my answer is incorrect. I think the reason it's difficult is because it intuitively doesn't make sense, ...heading 90 degrees south after initially traveling due east, not to mention...
  20. E

    Conservation of momentum and HUP in PET

    "When a positron emitted in beta+ decay annihilates with an electron, the combined mass of the two particles, m = 2me, is converted into an amount of energy 2mec^2 in the form of two 511 keV gamma rays. Momentum conservation requires that the two gamma ray photons are emitted in opposite...
  21. K

    Is This a Conservation of Angular Momentum Problem?

    i don't know how to solve this problem is it a conservation of momentum problem? because can't you just use mv=mv?
  22. B

    Conservation of Momentum problem needs quick reply

    Okay, here's the problem: A 24 g bullet is fired horizontally, embedding itself in a 10 kg block initally at rest on a horizontal ice surface. The block slides the ice, coming to rest in 2.0 s at a distance of 60 cm from its original position. Assuming that the frictional force stopping the...
  23. S

    Conservation of Momentum Question

    PLEASE, please help! I have been working on this problem for two days and am about to pull my hair out. This is a distance course, so I have no one to ask for help. I am trying to solve a conservation of linear momentum problem in which there are two unknowns. Object 1 (0.5 kg), going 7.0...
  24. C

    Conservation of momentum - Collision of pool balls

    Hi, I am having trouble recalling my concepts in momentum. I just remember its conserved :rolleyes: Plus, I am horrible with directions, so need help understanding this problem, as well as the underlying concepts. Two pool balls are rolling along a pool table. The orange pool ball has...
  25. W

    Conservation of momentum and isolated systems

    I was reading on the conservation of momentum and they mention how in isolated systems momentum is always conserved and if the external forces of the system is zero. In the case of friction or drag acting against the motion of a body would that be considered as part of the isolated system or an...
  26. F

    Conservation of Momentum (Linear and Angular)

    On a frictionless table, a glob of clay of mass 0.38 kg strikes a bar of mass 1.76 kg perpendicularly at a point 0.12 m from the center of the bar and sticks to it. If the bar is 0.66 m long and the clay is moving at 5.7 m/s before striking the bar, what is the final speed of the center of...
  27. I

    Conservation of momentum of a raft

    hi! i'm having trouble solving this problem...hopefully someone can at least get me started A raft of mass 180 kg carries two smimmers of mass 50 kg and 80 kg. The raft is initially floating at rest. The two swimmers simultaneously dive off opposite ends of the raft, each with a horizontal...
  28. C

    Shouldn't Conservation of Momentum Be Conserved in this Problem?

    Shouldn't Conservation of Momentum Be Conserved in this Problem? Alright, I am deeply confused on this problem. It goes like this: A big sledge is standing at rest on a horizontal icy surface. A rail is placed in such a way that the sledge can move only along a straight line. It is assumed...
  29. Crumbles

    Simple question on Conservation of Momentum and KE

    I am having a bit of a conceptual problem with the conservation laws. Consider a system of two bodies of mass m each. One moving at speed V1 towards the second body which is at rest. For the case of an inelastic collision, I understand that the total kinetic energy of the system is not...
  30. F

    Conservation of momentum of a rocket

    The last stage of a rocket is traveling at a speed of 8000 m/s. This last stage is made up of two parts that are clamped together, namely, a rocket case with a mass of 330.00 kg and a payload capsule with a mass of 155.00 kg. When the clamp is released, a compressed spring causes the two parts...
  31. K

    Conservation of momentum and energy

    Conservation of momentum and energy :D :frown: Wats this question on bout? 1. [HRW6 10.P.026.] In Fig. 10-32a, a 4.00 g bullet is fired horizontally at two blocks at rest on a frictionless tabletop. The bullet passes through the first block, with mass 1.20 kg, and embeds itself in the...
  32. F

    Elastic Collision and conservation of momentum

    In an elastic collision between two objects. Show that the speed of approach is equal to the speed of seperation. I know you have two equations, the conservation of momentum and the conservation of kinetic energy, but I wouldn't know how to solve the equations.
  33. A

    Rocket Problem - Law Of Conservation Of Momentum

    Hi, I am unable to solve this problem. :zzz: I applied Law of Conservation of Momentum but unable to get the related answer. The problem is as. :!) "A rocket is moving vertically upward. % Kg fuel gas is released out of it in downward direction with a velocity of 5000 m/s. If the...
  34. F

    Conservation of Momentum: Falling object

    Does a ball falling to Earth violate conservation of momentum?
  35. A

    Explaining Newton's Cradle: Proving Conservation of Momentum & KE

    im working on a mathematical model of Newton's cradle. I am trying to explain mathematically why, when two balls are released, two balls pop up the other side etc. i said that if there are N balls in the cradle, each with mass m, and the two balls you displace have gained a velocity v by the...
  36. G

    Conservation of momentum formula

    A block (A) collides with block (B). The blocks were in contact for 0.25 seconds. So what is the force exerted on block (A) by block (B)? I used the formula for impulse and set it equal to the momentum. But it requires a change in velocity for it to work. I already know the velocity of each...
  37. 7

    Conservation of Momentum of a uniform thin rod

    A uniform thin rod of length 0.40 m and mass 3.5 kg can rotate in a horizontal plane about a vertical axis through its center. The rod is at rest when a 3.0-g bullet traveling in the horizontal plane of the rod is fired into one end of the rod. As viewed from above, the direction of the bullet's...
  38. C

    Is this conservation of momentum?

    The problem is: A uniform thin rod of length = .5m and mass M = 4.0kg can rotate in a horizontal plane about a vertical axis through its center (I = ML^2/12). The rod is at rest when a bullet of mass m = 3.0g traveling in the horizontal plance of the rod is fired into one end of the rod. As...
  39. G

    Conservation of momentum cannon problem

    A cannon rigidly attached to a carriage, whic can move along horizontal rails but is connected to a post by a large initially unstreched spring with a force constant k=2x10^4N/m. The cannon fires a 200kg projectile at a velocity of 125m/s directed 45 degrees above the horizontal. a) If the...
  40. J

    Help with conservation of momentum question

    A circus cannon, which has a mass M = 2500 kg, is tilted at q = 35°. When it shoots a projectile at v0 = 30 m/s with respect to the cannon, the cannon recoils along a horizontal track at vcannon = 2 m/s with respect to the ground. a) At what angle to the horizontal does the projectile move...
  41. L

    Conservation of Momentum and Energy

    This one is giving me fits for some reason: A proton of mass m undergoes a head-on collision with a stationary carbon nucleus of mass 12m. The speed of the proton is 300 m/s. Find the velocity of the proton after the collision. Ok, I know that both momentum and energy are conserved. So...
  42. F

    Law of conservation of momentum

    I can't seem to figure out what the damn question is asking :D. Can anyone explain what the question is asking? During a chicago storm, winds can whip horizontaly at speeds of 100 km/h. If the air strikes a person at the rate of 40kg/s per square meter and is brought to rest, calculate the...
  43. L

    Conservation of Momentum problem

    I'm not sure what I've done wrong on this problem, so anyone who sees my mistake, please let me know! Two blocks are moving on a frictionless surface. The first block's mass is 1.17 kg and its initial velocity is 5.50 m/s. The second block's mass is 2.73 kg and its initial velocity is 2.15...
  44. M

    Conservation of Momentum Question

    undefinedundefinedundefined A boat of mass m is carrying a load of bricks with a total number of N and mass M, and is floating freely on water. SUPERMAN, in a show of strength, throws the entire load of bricks backward at once with a relative speed of v0. A GENIUS, in a show of intelligence...
  45. P

    Momentum and Conservation of Momentum

    Whew, I finished the kinetic and power problems thanks to the help of marlon and arildno, but now I have some questions on momentum. Hopefully this will help others who need help with the concept. Firstly, I have some questions on basic principle to get down(I'm hoping I got these right as...
  46. A

    Easy physics thinking question (conservation of momentum)

    Two football players run into each other at midfield. We can (or cannot) realistically apply conservation of momentum to calculate the players' velocities just after the impact because A. The system of interest floats in space. B. The players are functionally isolated. C. We can treat...
  47. B

    Conservation of Momentum in a Spaceship Explosion

    Hi all, I have become frusturated at a conservation of momentum problem. A space ship(ss) with a mass of 2.0*10^6 [kg] is crusing at a speed of 5.0*10^6 [m/s], when it blows up. One section(s1), with mass 5.0*10^5 [kg] is blown straight backwards at a speed of 2.0*10^6 [m/s]. The second...
  48. R

    Conservation of momentum of plate drop

    Hi, i was wondering if anybody can help me with the following problem: A plate drops onto a smooth floor and shatters into 3 pieces of equal mass. 2 of the pieces go off with equal speeds v at right angles to one another. How do I find the speed and direction of the third piece? I know...
  49. D

    I have a conservation of momentum equation Q

    I have a conservation of momentum equation Q! A 0.25kg skeet (clay target) is fired at an angle of 30 degrees to the horizon with a speed of 30 m/s. When it reaches its maximum height, it is hit from below by a 15g pellet traveling vertically upward at a speed 200m/s, the pellet is imbedded in...
  50. tandoorichicken

    Conservation of momentum on merry-go-round

    A playground merry-go-round has a disk-shaped platform that rotates with negligible friction about a vertical axis. The disk has a mass of 200kg and a radius of 1.8 m. A 36-kg child rides at the center of the merry-g-round while a playmate sets it turning at 0.25 rev/sec. If the child then walks...
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