# Tagged Questions

In introductory mechanics, the momentum of a particle is its mass times its velocity. In electrodynamics, the momentum of a field is proportional to the cross-product of the electric field with the magnetic field. In special relativity, momentum is generalized to four-momentum.

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### Integrals of motion for a free particle

I'm struggling to understand the argument on p. 13 in Landau and Lifshitz that for a system with $N$ degrees of freedom there must be $2N-1$ integrals of motion. In particular, I can't understand ...
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### Why Use the Non-Relativistic Momentum Operator in Relativistic Quantum Mechanics?

In deriving the Klein Gordon equation one starts out with the relativistic energy relation E^2 = p^2 + m^2 and substitutes the quantum momentum operator that corresponds to non-relativistic QM, p = -i ...
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### What is the effective electron mass in a plasma?

Is there a way to calculate the effective electron mass in plasmas? Effective electron mass is usually defined as varying from the vacuum electron mass in solid state physics. However, momentum ...
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### What happens to Newton's Third Law during the reflection of a pulse from a free end?

Well, it is known that a pulse gets inverted when it gets reflected from a fixed support while the polarity of the pulse remains same when the incident pulse gets reflected from a free end. However, ...
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### Momentum Twistor variables and non-planar theory

I know that the use of twistur-momentum variables makes manifest the arising of certain poles in scattering amplitudes: if the sum of external momenta $P_I = p_i + p_{i+1} + ... + p_j$ is going on-...
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### Equating $\frac{dp}{dt}$ and $F$ at a hydraulic jump?

A journal I am reading about circular hydraulic jumps provides the equation and I quote: $H$= Depth after hydraulic jump, $h$= depth before hydraulic jump, $V$= velocity after hydraulic jump, $v$= ...
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### Can deformations of time-space continuum violates law of momentum conservation?

Based on Einsteinâ€™s theory of relativity a mass as property of physical objects creates deformation of time-space continuum. Therefore the light path bends in gravitational fields of massive objects. ...
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### How could you slow down or change direction with photonic propulsion?

So you have a laser shooting at a sort of solar sail to transfer momentum in the forward direction but could you have an onboard laser and turn the laser around to hit another sail? How could you turn ...
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### Relating Initial velocity and acceleration to distance traveled up a ramp

This is the situation: I am conducting research on the ability of fin-fish to scale short wetted ramps for use alongside sea-lamprey barriers to allow non-target species to pass these barriers. We ...
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### Why is a network pattern (weaving pattern) stronger than a whole solid surface of the same material

For example badminton racquets and huts.
An object ofass $5$ kg is projected with a velocity of $20m/s$ at an angle of $60degress$ to the horizontal. At the highest point of its path projectile explodes and breaks up into $2$ fragments of ...