# What is Conservation of momentum: Definition and 756 Discussions

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.

View More On Wikipedia.org
1. ### I How Feynman proves momentum is conserved in this example?

Here is what Feynman says, "Suppose we have two equal masses, one moving with velocity v and the other standing still, and they collide and stick; what is going to happen? There is a mass 2m altogether when we are finished, drifting with an unknown velocity. What velocity? That is the problem...
2. ### I Current through U-wire (rail gun): Violation of (naive) conservation of momentum?

Hi. I had a question about railguns, but I think I can formulate the underlying problem more clearly and concisely, hence I'm opening a different thread. Consider the following rigid arrangement of three pieces of wire and two parallel capacitor plates: There's an open switch somewhere in the...
3. ### Conservation of Momentum Calculation Woes!

Alleyway kick The kicker weighs approximately 64kg or 140lb and the gentlemen holding the air shield is approximately 73kg or 160lb. How far does the kickee travel before hitting the chair and boxes and what speed is he travelling at? The practice kick prior to the actual kick puts the men...
4. ### I Stress-energy tensor and energy/momentum conservation clarification

I've been working through Bernard Schutz's book on GR and have run into some confusion in chapter 4 problem 20 part b. In this chapter, the stress-energy tensor for a general fluid was introduced and was used to derive the general conservation law for energy/momentum, where we found that...

32. ### Does density of a medium affect the conservation of momentum?

Hi all, If a body has a given initial momentum and then travels through a continuously less dense medium would it's velocity increase to conserve momentum? Thanks Jerry
33. ### Conservation of momentum and energy problem

In an elastic collision, a 400-kg bumper car collides directly from behind with a second, identical bumper car that is traveling in the same direction. The initial speed of the leading bumper car is 5.60 m/s and that of the trailing car is 6.00 m/s. Assuming that the mass of the drivers is...
34. ### Conservation of angular momentum and its counterpart for linear momentum

Hi, I have just joined the forum. Thank you all for being a part of such places so that people like me can get answers to the questions on their minds! --------------------------- I have been trying to understand how a quadcopter yaws. Referring to the figure below which is bird's eye view of...
35. ### Cars Collide on a Hill, Conservation of Momentum

QUESTION: ----------- For the purposes of this problem, we will define the direction of Vehicle A's initial velocity as the positive direction: While driving on a road that is inclined at an angle of 10 degrees above the horizontal, Vehicle A and Vehicle B are in a head-on collision lasting...
36. ### I Does Conservation of Momentum & Energy Hold in the C.O.M. Reference Frame?

We know classical equations fail to follow conservation of momentum and energy when we are dealing with speeds closer to the speed of light. But does it fail in the center of mass reference frame of a system?
37. ### Is 2D Conservation of Momentum Possible? A Visual Analysis

I am unable to find any angle for which the horizontal and vertical components of the linear momentum are conserved. I have added an image of my attempt
38. ### Conservation of momentum — Water dropped from a firefighting airplane

I could not unserstand part d.Does problem ask about plane's speed immediately after it starts to drop water or after the water is dropped completely?
39. ### Conservation of momentum when a ball hits a wall

I think we can.Although the wall is not moving, it is just because the wall has a huge mass.As rhe law of the conservation of momentum states(suppose the ball hits the wall from the left), when the momentum decrease by J, the momentum of the wall increase by J, which means the momentum of the...
40. ### Conservation of Momentum involving Vf, elastic collisions

I tried solving it using this method and I got 12.5m/s, and assumed the collision was elastic. The answer is actually 6.32m/s [41.5 degrees counterclockwise from the original direction of the first ball]; the collision is not elastic: Ek = 12.1J Ek`= 10.2J I have absolutely no idea how the...
41. ### Conservation of momentum in a bullet-block-spring system

According to the first equation, the final potential energy is equal to the initial kinetic energy of the block. So that means that Vblok is the instantaneous speed of the block right before it moves to the right and compress the spring, right? But doesn't the second equation (The initial total...
42. ### Simple Canon Question (Conservation Of Momentum): Frame of Reference

Since Pi = Pf, 0 = MbVbg + McVcg I just need to express Vbg in terms of Vbc and Vcg (that is, I need to express the velocity of the ball relative to the ground in terms that I know/want to solve for): by reference frames: Vbc = Vbg + Vcg so Vbg = Vbc -Vcg Now I can sub in and solve 0 =...
43. ### Conservation of Momentum: Elastic Collision of Two Masses

I really want to know which answer is correct. I don’t really know if I should include velocities to the left as negative velocities in the equation. Is it -1 or 4.33? Please help! Thanks!
44. ### Conservation of Momentum vs Constant k for an Ideal Spring

I encountered a weird conflict between my thought process and that of author's solution in book: The common viewpoint of both of us were invoking conservation of energy of this SHM system But the author proceeds to solve it using conservation of momentum, taking the new mass added to system as...
45. ### Conservation of momentum and energy

So to start off, the piece that hits the ground first is the smaller piece. So I can form the equations where: where ##8(u_{8kg})= m_{1}v_{1}+m_{2}v_{2}## ##m_{1}+m_{2}= 8## After 2 seconds, ##30 = v_{1}(2)+\frac{1}{2}at^{2}## ##v_{1}= 5.2m/s## ##(30-16) = v_{2}(2)+\frac{1}{2}at^{2}## ##v_{2}=...
46. ### Laws of conservation of momentum?

Problem Statement: Are this 3 topics comes under laws of conservation of momentum? Relevant Equations: Are this 3 topics comes under laws of conservation of momentum? Are this 3 topics comes under laws of conservation of momentum: energy lost due to impact, inelastic impact, purely elastic...
47. ### Wet wheel and conservation of momentum

A cyclist coasts along a road, he drives across a small puddle of water, after which the wheels leave wet lines on the road. Now we concentrate our attention to the linear momentum of the water on a wheel. It decreases. Momentum is conserved, so what got the momentum that the water had?
48. ### Conservation of Momentum (Elastic Collisions)

Part (iii) is the part I am stuck on and is a 5 mark question. I have some idea of how to attempt it shown below momentum is conserved so mux = mvy + mvz (where ux is the initial velocity before the collision of ball x, vy is the velocity after the collision of ball y and vz is the velocity...
49. ### Orbital Slingshot and Conservation of Momentum Confusion

Hello, I am an undergrad and am in an introductory level astrophysics course. I have a bit of confusion that I didn't know where to get help from so I made an account here. Please let me know if I miss some common etiquette or something... I don't understand how the slingshot maneuver...
50. ### Do Neutrinos Leave Tracks in Cloud Chambers?

My only issue is what this would look like. I can't draw a respective picture.